Hayden Stewart

Diansheng Dong

Andrea Carlson

Economic

Research

Service

Economic 

Research

Report 

Number 149

May 2013

United States Department of Agriculture

Why Are Americans Consuming Less 

Fluid Milk? A Look at Generational 

Differences in Intake Frequency
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Stewart, Hayden, Diansheng Dong, and Andrea Carlson. Why Are Americans 

Consuming Less Fluid Milk? A Look at Generational Differences in Intake 

Frequency, ERR-149, U.S. Department of Agriculture, Economic Research 

Service, May 2013.

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United States Department of Agriculture
Economic 

Research 

Service

Economic

Research

Report

Number 149

May 2013

Abstract

Americans are drinking less fluid milk, on average. In this study, ERS researchers find 

that declining consumption since the 1970s reflects changes in the frequency of fluid milk 

intake, rather than changes in portions. USDA survey data collected between 1977 and 

2008 reveal that Americans are less apt to drink fluid milk with their midday and nighttime meals than in earlier years, reducing the total number of consumption occasions per 

day. Moreover, more recent generations of Americans show greater decreases in consumption frequency, holding constant other factors such as education and race. The majority of 

Americans born in the 1990s consume fluid milk less often than those born in the 1970s, 

who, in turn, consume it less often than those born in the 1950s. All other factors constant, 

as newer generations with reduced demand gradually replace older ones, the population’s 

average level of consumption of fluid milk may continue to decline.

Keywords: fluid milk, fluid milk demand, fluid milk products, intake frequency, 

consumption frequency, generational change, cohort effects, portion sizes, milk drinking, 

dairy products, dairy checkoff, school lunches, consumer habits, childhood habits

Acknowledgments

The authors extend their thanks for comments from Dennis Clason, New Mexico State 

University; Joseph Balagtas, Purdue University; Hiroshi Mori, Senshu University; Mark 

Lino, USDA, Center for Nutrition Policy and Promotion; and Lisa Mancino, USDA, 

Economic Research Service. We also thank Maria Williams for editorial service and 

Cynthia A. Ray for design.

Hayden Stewart

Diansheng Dong

Andrea Carlson

Why Are Americans Consuming Less 

Fluid Milk? A Look at Generational 

Differences in Intake Frequency

United States Department of Agriculture
ii Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Contents

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Identifying Trends in the Frequency and Quantity of Fluid Milk 

Consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Modeling Trends in Fluid Milk Consumption Across the Generations. . . . . . . . 11

Variables Used in the Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Model Specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Estimating the Model and Examining Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Generational Change Contributing to Decreases in Consumption 

Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Portions Remaining Largely Stable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Considering the Health Implications of Trends in Milk Consumption. . . . . . . . . 22

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Appendix I: Comparing Consumption Across Different USDA Dietary 

Intake Surveys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Appendix II: Model Specification and Estimation. . . . . . . . . . . . . . . . . . . . . . . . . . 28
United States Department of Agriculture

A report summary from the Economic Research Service May 2013

ERS is a primary source 

of economic research and 

analysis from the U.S. 

Department of Agriculture, 

providing timely information on economic and policy 

issues related to agriculture, 

food, the environment,and 

rural America. www.ers.usda.gov

Why Are Americans Consuming Less 

Fluid Milk? A Look at Generational 

Differences in Intake Frequency

Hayden Stewart, Diansheng Dong, and Andrea Carlson

What Is the Issue?

Most Americans do not consume enough dairy products. The Dietary Guidelines for Americans, 

2010 recommends 2 cup-equivalents per day for children aged 2 to 3 years, 2.5 for those aged 

4 to 8 years, and 3 for Americans older than age 8. However, per capita dairy consumption has 

long held steady at about 1.5 cup-equivalents, despite rising cheese consumption. This stasis in 

per capita dairy consumption results directly from the fact that Americans are drinking progressively less fluid milk. Since 1970 alone, per capita fluid milk consumption has fallen from 0.96 

cup-equivalents to about 0.61 cup-equivalents per day. 

The Federal Government encourages dairy consumption, including fluid milk, cheese, and yogurt, 

among other foods, through the Dietary Guidelines for Americans, 2010. Special emphasis is 

placed on fat-free and low-fat products. USDA further supports this message through programs 

like the National School Lunch Program (NSLP). The NSLP stipulates that schools must provide 

fluid milk and it must be low-fat or skim, rather than whole. Dairy farmers and fluid milk processors are also working to promote dairy products. The popular “Got Milk?” campaign, for one, 

encourages drinking fluid milk. 

This report examines trends in Americans’ fluid milk consumption, including average portion 

sizes and generational differences in the frequency of milk drinking, to investigate possible 

explanations for the continued decreases.

What Did the Study Find?

Data from USDA dietary intake surveys conducted between the 1970s and 2000s show that 

Americans—on occasions when they drink fluid milk—continue to consume about 1 cup (8 

fluid ounces). Given the stability of portions, trends showing decreases in per capita consumption since the 1970s mainly reflect changes in consumption frequency. Between the 1970s and 

2000s, people have become less apt to drink fluid milk at mealtimes, especially with midday and 

nighttime meals, reducing the total number of consumption occasions:

• Between surveys in 1977-78 and 2007-08, the share of preadolescent children who did not 

drink fluid milk on a given day rose from 12 percent to 24 percent, while the share that drank 

milk three or more times per day dropped from 31 to 18 percent. 

Find the full report 

at www.ers.usda.

gov/publications/erreconomic-researchreport/err-149.aspx

Hayden Stewart

Diansheng Dong

Andrea Carlson

Economic 

Research 

Service

Economic 

Research 

Report 

Number 149

May 2013

United States Department of Agriculture

Why Are Americans Consuming Less 

Fluid Milk? A Look at Generational 

Differences in Intake Frequency
• Between 1977-78 and 2007-08, the share of adolescents and adults who did not drink fluid milk on a given 

day rose from 41 percent to 54 percent, while the share that drank milk three or more times per day dropped 

from 13 to 4 percent. 

Underlying these decreases in consumption frequency are differences in the habit to drink milk between newer 

and older generations. All else constant (e.g., race and income), succeeding generations of Americans born 

after the 1930s have consumed fluid milk less often than their preceding generations:

• Americans born in the early 1960s consume fluid milk on 1.1 fewer occasions per day than those born 

before 1930. 

• Americans born in the early 1980s consume fluid milk on 0.3 fewer occasions per day than those born in 

the early 1960s. 

Differences across the generations in fluid milk intake may help account for the observed decreases in per 

capita fluid milk consumption in recent decades despite public and private sector efforts to stem the decline. 

Furthermore, these differences will likely make it difficult to reverse current consumption trends. In fact, 

as newer generations replace older ones, the population’s average level of fluid milk consumption may 

continue to decline.

How Was the Study Conducted?

ERS researchers pooled data from five USDA dietary intake surveys for analysis. These included the 1977-78 

Nationwide Food Consumption Survey, the 1989-1991 Continuing Survey of Food Intakes by Individuals 

(CSFII), 1994-1996 CSFII, the 2003-04 National Health and Nutrition Examination Survey (NHANES), 

and the 2007-08 NHANES. Respondents in each survey were asked to report their intake of all foods and 

beverages on one or more days. This study focused on individuals’ fluid milk consumption during a single, 

24-hour period. 

Researchers reviewed the existing literature on fluid milk demand, compared consumption data across periods 

in the different surveys, and then conducted a formal hypothesis test for whether newer generations are 

consuming fluid milk fewer times per day, and whether changes in portion sizes are also affecting consumption 

trends. This was accomplished by estimating an econometric model that predicts both the frequency and total 

quantity of fluid milk consumed by Americans who participated in USDA food consumption surveys, based on 

their birth year, race, household income, and demographic characteristics.

www.ers.usda.gov
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 1

Introduction

Most Americans do not consume enough dairy products. The Dietary Guidelines 

for Americans, 2010 recommends 2 cup-equivalents per day for children aged 2 

to 3 years, 2.5 for those aged 4 to 8 years, and 3 for Americans older than age 8. 

By contrast, actual dairy consumption has held steady between 1.45 and 1.55 cupequivalents per capita since the 1970s, despite a near tripling of cheese consumption 

over the past 40 years (USDA-ERS, 2013a). The reason for this stasis in overall 

dairy consumption is that Americans are drinking progressively less fluid milk. 

Long a dietary staple, fluid milk once accounted for the majority of overall dairy 

consumption. However, as chronicled by Popkin (2010, p. 1), there has been a 

“slow continuous shift downward” in milk drinking since the 1940s. Since 1970 

alone, per capita consumption has fallen from 0.96 to 0.61 cup-equivalents per 

day (USDA-ERS, 2013a). Moreover, this trend appears to cut across different age 

groups. Younger people aged 2 to 18 years consumed less fluid milk in the 2000s 

than did children and adolescents in the 1970s (Cavadini et al., 2000; Popkin, 

2010).1 Adults (over 18) have also been consuming less fluid milk over time (Enns 

et al., 1977; Popkin, 2010). 

The Federal Government encourages dairy consumption, including fluid milk, 

cheese, and yogurt, among other products, through the Dietary Guidelines for 

Americans, 2010.

2 Special emphasis is placed on consuming more fat-free and 

low-fat milk and milk products in particular. These foods provide many of the same 

nutrients as higher fat dairy products with fewer calories (p. 38). 

USDA further supports its dairy message through programs like the National School 

Lunch Program (NSLP), the Special Supplemental Nutrition Program for Women, 

Infants, and Children (WIC), and the Special Milk Program. The NSLP, for one, 

requires participating schools to offer students low-fat or skim fluid milk—and no 

whole milk. Only skim milk may be flavored (e.g., strawberry or chocolate). 

Like the Federal Government, dairy farmers and fluid milk processors are concerned 

about low levels of dairy consumption. Both invest in checkoff3 programs to 

increase sales of and demand for dairy products and ingredients (National Dairy 

Promotion and Research Board, 2013). Some efforts supported by checkoff 

programs focus primarily on fluid milk, including the popular “Got Milk?” 

campaign. Others like “Fuel Up to Play 60” emphasize all dairy products consump1Popkin (2010) examined the consumption of milks, sugar-sweetened beverages (SSB), 

diet beverages, juices, alcoholic beverages, and unsweetened tea and coffee. SSBs include 

carbonated and uncarbonated soft drinks, sugared waters, and energy drinks, among others. He studied consumption trends for children and adolescents aged 2 to 18 years. Popkin 

(2010) separately examined beverage consumption for adults aged 19 and older. 

2The Dietary Guidelines for Americans, 2010 are issued by USDA and the U.S. Department of Health and Human Services (DHHS) to provide evidence-based nutrition information 

and advice for people age 2 and older. They also serve as the nutritional basis for Federal 

food and nutrition assistance education programs. 

3A checkoff program collects funds from producers of a particular agricultural commodity 

and uses these funds to promote and conduct research on that commodity.
2 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

tion, including milk drinking. This particular initiative encourages children to be 

physically active and “fuel up” with nutrient-rich foods like low-fat and skim milk, 

cheese, and yogurt. Dairy farmers contribute $0.15 per 100 pounds of milk they 

commercially market to checkoff programs, while fluid milk processors contribute 

$0.20 per 100 pounds they sell in consumer-type packages. Yet, so far, the efforts 

of dairy farmers, fluid milk processors, and the Federal Government have not 

increased dairy consumption to recommended levels, while fluid milk consumption 

continues to fall.

Previous research on declining fluid milk consumption—the main reason for 

stationary dairy consumption levels—finds that generational differences (“cohort 

effects”) are a contributing factor. Using dietary intake surveys collected by USDA 

between the 1970s and the 2000s, Stewart et al. (2012) recently demonstrated that 

more recent generations consume smaller quantities of fluid milk. For example, 

on average, Americans born in the 1980s consume less fluid milk per day than 

Americans born in the 1960s, holding constant other factors such as income and 

race. These findings may reflect the persistence of childhood habits—each successive generation grows up less accustomed than their parents to drinking fluid milk 

and carries that habit forward into adult life. 

In this study, ERS researchers used USDA dietary intake surveys from the 1970s, 

1980s, 1990s, and 2000s to identify the number of times per day that Americans 

consume fluid milk, as well as to identify portion sizes. A possible explanation 

for decreases in the quantity of fluid milk consumed over time is that Americans 

are consuming it fewer times per day. However, Americans may also be using 

fluid milk in different ways. For example, if Americans consume fluid milk more 

often than they used to as a snack in a coffee drink and less often as a standalone 

beverage at mealtimes, then average portion sizes could change. Given Stewart et 

al.’s (2012) findings on generational change, the researchers also tested whether 

newer generations are consuming fluid milk less frequently than older generations. 
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 3

Identifying Trends in the Frequency and Quantity of Fluid 

Milk Consumption

To monitor trends in the American diet, ERS estimates the quantities of foods available for consumption annually (USDA-ERS, 2013b). ERS food availability data 

suggest that Americans have been consuming less fluid milk since the 1940s. Data 

on per capita consumption since the 1970s (USDA-ERS, 2013a)4 reveal a decrease 

in average consumption from about 0.96 cups to about 0.61 cups of fluid milk 

per day over the past 40 years (fig. 1). Increases in the consumption of 2-percent, 

1-percent, and skim milk have partly offset decreases in whole milk consumption.5

These products are hereafter referred to as lower fat milk. Consumption of lower fat 

milk products accounted for about 20 percent of total consumption in the 1970s and 

about 70 percent by the end of the 2000s. 

4These data are created by adjusting food availability data for food spoilage and other 

forms of food loss to better proxy for consumption. Loss-adjusted food availability data are not 

available prior to 1970.

5Whole milk has a minimum fat content of 3.25 percent. ERS researchers were not able 

to separately identify consumption trends for 2 percent (reduced-fat), 1 percent (low-fat), and 

skim milk. As noted in the text above, current dietary recommendations place special emphasis on low-fat and skim milk. 
4 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Trends in fluid milk consumption can also be examined using USDA dietary 

surveys intermittently collected since the 1970s. Unlike ERS food availability data, 

these surveys break down food consumption data by particular segments of the 

population, such as children. Survey participants provided their household income, 

age, educational attainment, race, and ethnicity, among other characteristics. They 

also provided one or more 1-day “dietary recalls.” These recalls include information 

on the foods and beverages consumed by the individual on the previous day. 

The information provided shows how many times fluid milk was consumed, and 

whether each consumption occasion was part of a meal or snack. It is also possible 

to estimate the amounts of fluid milk consumed as a beverage, in cereal, or even as 

an ingredient in a food, such as a soup.6 In this study, the researchers focused on 

individuals’ fluid milk consumption over the 24-hour period covered by their initial 

1-day dietary recall. 

ERS limited the analysis to the consumption of plain and flavored fluid milk 

consumed alone as a beverage, put in cereal, poured in coffee, or used as an ingredient in selected coffee drinks.7 In 2007-08, these products accounted for 93 percent 

of all fluid milk consumed by survey participants in all uses. Excluded from the 

study were milk in eggnog, malted milk, milkshakes, weight loss shakes, soups, 

and baked goods, among other foods. Also excluded from the results reported in 

this study were soy beverages.8 USDA dietary records distinguish among whole, 

2-percent, 1-percent, skim, and other types of fluid milk, though survey participants cannot always recall which type of milk they consumed. See also Appendix I: 

Comparing Consumption Across Different USDA Dietary Intake Surveys.

ERS analysis of USDA food consumption surveys collected since the 1970s 

confirms that fluid milk intake has declined for preadolescent children (aged 2 to 

12 years), as well as for Americans beyond childhood (fig. 2). In 1977-78, preadolescent children drank, on average, 1.7 cups per day, while in 2007-08 children this 

age drank only 1.2 cups per day (30 percent less). Similarly, in 1977-78, Americans 

aged 13 and over drank, on average, 0.8 cups per day, while in 2007-08, people 

this age drank only 0.6 cups (25 percent less). USDA dietary intake surveys also 

confirm that milk drinkers in 2007-08 were more likely to choose a lower fat 

product than milk drinkers in 1977-78 (fig. 3). 

To better understand declining fluid milk consumption, ERS examined how often 

Americans consume fluid milk at mealtimes (table 1). For example, in 1977-78, 

39 percent of adolescents and adults drank milk with a morning meal; 24 percent 

consumed it with a midday meal; and 21 percent had fluid milk with a nighttime 

6Recipes developed for use with more recent food consumption surveys are available in 

the USDA Food and Nutrient Database for Dietary Studies (FNDDS). See USDA, Agricultural 

Research Service (2013a).

7Includes only coffee drinks that are 50 percent or more milk such as a latte (75 percent 

milk), café con leche (51 percent), mocha (66 percent), cappuccino (51 percent), and sweetened milk coffee with ice (58 percent).

8Americans consume only a small amount of soy beverages compared with their consumption of cow’s milk. ERS researchers confirmed that including the former in the analysis 

would not significantly affect the study’s results. 
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 5

meal.9 By 2007-08, those percentages had decreased to 28 percent, 8 percent, and 9 

percent, respectively. 

From the same two surveys, similar trends were seen in the consumption habits of 

preadolescent children. In the later survey, young children consumed fluid milk 

with fewer meals (especially, fewer midday and nighttime meals) than did the 

young children of the earlier survey. However, unlike adolescents and adults, young 

children have partly offset mealtime decreases in milk consumption with increases 

while snacking. 

In total, Americans consumed fluid milk less frequently in 2007-08 than they did in 

1977-78 or 1994-96 (fig. 4). Over the 30 years between 1977-78 and 2007-08, the 

share of individuals not consuming any fluid milk on a given day rose from 12 to 24 

percent among preadolescent children, and from 41 to 54 percent among adolescents 

and adults. Furthermore, the shares consuming fluid milk several times a day fell. 

By 2007-08, only 45 percent of preadolescent children and 14 percent of adolescents and adults consumed fluid milk on more than one occasion. 

Besides consuming milk less often, Americans may be changing their fluid milkdrinking habits in other ways, but so far, those changes have had little effect on 

portion sizes. ERS researchers hypothesized that, if individuals are consuming fluid 

milk more often in a coffee beverage than they used to and less often as a standalone 

beverage at meals than they used to, average portion sizes may change. 

9Midday meal is defined as a meal occasion occurring between 11 a.m. and 5 p.m.
6 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Nonetheless, from the data available, ERS finds that, on the occasions when 

Americans do consume fluid milk, they have continued to drink at least as much as 

they did in the 1970s (fig. 5). Americans drank about 1 cup (8 fluid ounces) of fluid 

milk per occasion in 2007-08, on average, versus 0.8 cups in 1977-78. That portions 

appear not to have decreased, in turn, suggests that decreases in the frequency of 

consumption, shown in table 1 and figure 4, primarily underlie the downward trend 

in intake, shown in figures 1 and 2. 
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 7

Table 1

Americans less apt to consume fluid milk at mealtimes1

Percentage of preadolescent children consuming fluid milk

Morning meal Midday meal2 Night meal Snack

1977-78 NFCS 71.3 50.7 35.5 19.9 

(0.6) (0.7) (0.7) (0.5)

1989-91 CSFII 68.0 41.8 29.4 18.2 

(1.3) (1.4) (1.3) (1.1)

1994-96 CSFII 64.0 33.7 23.5 21.0 

(0.9) (0.9) (0.8) (0.8)

2003-04 NHANES 57.4 26.7 22.1 26.4 

(1.9) (1.7) (1.6) (1.7)

2007-08 NHANES 55.6 29.3 17.5 24.7 

(1.7) (1.5) (1.3) (1.4)

Percentage of adolescents and adults consuming fluid milk

Morning meal Midday meal2 Night meal Snack

1977-78 NFCS 38.8 24.0 21.5 13.2

(0.4) (0.4) (0.3) (0.3)

1989-91 CSFII 38.1 14.9 14.1 11.3

(0.7) (0.5) (0.5) (0.4)

1994-96 CSFII 35.8 10.4 10.6 12.1

(0.6) (0.4) (0.3) (0.4)

2003-04 NHANES 28.9 7.4 9.3 14.4

(0.9) (0.5) (0.6) (0.7)

2007-08 NHANES 28.2 8.0 8.8 13.8

(0.8) (0.5) (0.6) (0.7)

1Standard errors reported in parentheses. 

2Midday meal is defined as a meal occasion occurring between 11 a.m. and 5 p.m.

Notes: Decreases in the percentages of individuals consuming fluid milk with their morning, midday, 

and nighttime meals between 1977-78 and 2007-08 are statistically significant at the 10-percent level 

for both age groups. 

Source: Calculated by the authors using the 1977-78 Nationwide Food Consumption Survey (NFCS), 

the 1989-1991 Continuing Survey of Food Intakes by Individuals (CSFII), the 1994-1996 CSFII, the 

2003-04 National Health and Nutrition Examination Survey (NHANES), and the 2007-08 NHANES and 

accompanying sample weights.

Overall, the data show that Americans are consuming fluid milk less frequently and, 

in turn, consuming smaller quantities, but what is driving these changes in behavior? 

Kaiser and Dong (2006) and Kaiser (2010) confirm that promotions sponsored by 

checkoff programs increase demand. Gleason and Suitor (2001) confirm a positive relationship between children’s participation in the NSLP and their fluid 

milk consumption. However, cohort effects may be exerting a greater impact on 

consumption in the opposite direction. 

Cohort effects exist when people belonging to the same generation make more 

similar food choices to each other than to people born farther from them in time. 

Since Schrimper (1979) first raised the possibility that cohort effects exist and 
8 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 9

shape trends in food consumption, much empirical research has followed. Mori et 

al. (2006) and Mori and Saegusa (2010) find that cohort effects influence fresh fruit 

and fish consumption in Japan. Stewart and Blisard (2008) find that they influence 

expenditures on fresh vegetables for at-home consumption in the United States.

As to cohort effects and fluid milk consumption, Stewart et al. (2012) find that more 

recent generations of Americans drink less fluid milk. For example, Americans born 

in the 1960s are consuming 0.13 cups less whole milk and 0.28 cups less lower fat 

milk per day than Americans born before 1930, holding constant other factors like 

race and income. Moreover, Americans born in the 1980s consume 0.16 cups less 

whole milk and 0.13 cups less lower fat milk per day than those born in the 1960s. 

Cohort effects could influence U.S. fluid milk consumption for several reasons. 

These reasons begin with the unique experiences of each generation of American 

children. Every decade brings a wider selection of beverage choices at supermarkets, restaurants, and other food outlets. Soft drinks, isotonic sports drinks, bottled 

water, and other products increasingly compete with fluid milk for a share of the 

consumer’s appetite. Changes have also occurred over time in the popularity of fast 

food, among other phenomena. 
10 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Changes in the food environment can affect children’s beverage consumption. 

Fisher et al. (2001) and Bowman et al. (2004) suggest that children’s fluid milk 

consumption may decrease with exposure to competing beverages and fast food, 

respectively. Regardless of other reasons, as successive generations of Americans 

have grown up amid declining rates of fluid milk consumption, they may have 

developed different life-long habits. The habit to drink milk may form (or not form) 

in childhood. According to the Dietary Guidelines for Americans, 2010, individuals 

“who consume milk at an early age are more likely to do so as adults” (p. 38).
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 11

Modeling Trends in Fluid Milk Consumption Across the 

Generations

Investigating consumption differences over time and across generations requires 

a particular type of data set. Many studies of U.S. food demand use time series 

data. These data typically span several decades and include information on food 

consumption or expenditures, price, and consumer income. However, time series 

data also tend to be highly aggregated. They do not typically contain information 

on individual consumers. By contrast, cross-sectional data contain information on 

individual consumers and may, therefore, be suitable for investigating the effects 

of demographic characteristics on demand. Nonetheless, because such data seldom 

span more than a couple years, they are not ideal for studying longrun trends. In 

Deaton’s (1997) terminology, researchers need a “time series of cross sections.” 

That is, they must pool cross-sectional surveys collected over several decades. 

Mori and Stewart (2011) empirically demonstrate the advantages of such data over 

traditional time series data. In this study, ERS pools the 1977-78 Nationwide Food 

Consumption Survey (NFCS), 1989-1991 Continuing Survey of Food Intakes by 

Individuals (CSFII), 1994-1996 CSFII, 2003-04 National Health and Nutrition 

Examination Survey (NHANES), and 2007-08 NHANES. 

A time series of cross-sectional surveys provides information on each generation’s 

food choices at various times in history and at different ages in their lives. For 

example, ERS researchers observed the number of times per day that members of 

different generations reported consuming fluid milk in the 1977-78 NFCS and in the 

2007-08 NHANES (fig. 6). As young children in 1977-78, Americans born in the 

1970s tended to consume fluid milk almost twice a day; and by 2007-08, as young 

adults in their 20s or 30s, they consumed it only 0.56 times per day. Despite their 

youth, Americans born in the 1970s consumed fluid milk even less often in 2007-08 

than members of some older generations. Over a 30-year span, Americans born in 

the 1940s decreased the frequency of their fluid milk consumption from about 0.97 

times per day (in 1977-78, in their 20s or 30s) to about 0.71 times per day (in 2007-

08, in their 50s or 60s). 

Previous studies, including Popkin (2010), Cavadini et al. (2000), and Stewart et al. 

(2012), have examined trends in the level of U.S. per capita fluid milk consumption. 

In this study, ERS researchers further investigated whether the smaller quantities 

of fluid milk being consumed by Americans are a result of their consuming it fewer 

times throughout the day. The researchers also confirmed whether trends in portion 

sizes likewise affect consumption levels. This was accomplished by estimating an 

econometric model that predicts both the frequency and total quantity of fluid milk 

consumed by Americans based on their generation (decade of birth), incomes, and 

demographic characteristics. Definitions and mean values are provided in table 2 for 

the model’s dependent and explanatory variables. In the next section, these variables 

are explained and the model outlined.
12 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Variables Used in the Analysis

The analysis focuses on fluid milk consumption by USDA survey participants over 

24 hours. The number of times that an individual drank fluid milk during this period 

is denoted as FREQUENCY. Preadolescent children consumed fluid milk on 1.65 

occasions, on average, with moderate person-to-person variation. FREQUENCY 

had a standard deviation of 1.2, among preadolescent children. By contrast, adolescents and adults consumed fluid milk 0.81 times, on average, with a standard deviation of 1.01. Of all survey participants, 58 consumed fluid milk on more than 6 

occasions. Three people consumed it on more than 10 occasions. The maximum 

value of FREQUENCY was 16 occasions. 

Also of interest was a survey participant’s total consumption of fluid milk. This 

dependent variable is denoted as QUANTITY. During the 24 hours covered by 

the dietary recall of preadolescent children, the children—including those who 

consumed no fluid milk at all—reported consuming 1.48 cups of fluid milk, on 

average, over all consumption occasions. Adolescents and adults consumed a total 

of 0.71 cups, on average. On the occasions when Americans do drink fluid milk, 

they may consume it in portions that are about what they were in the 1970s (see 

fig. 5). If portions have changed little, then changes over time in QUANTITY may 

reflect primarily changes in FREQUENCY.

The researchers also created explanatory variables to proxy for exogenous 

factors that may influence a person’s demand for fluid milk. FREQUENCY and 

QUANTITY were hypothesized to vary with a person’s income, demographic characteristics, and his or her decade of birth, among other factors. Extensive research 
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 13

Table 2

Mean values of variables used in the model

Children (age 2-12) Adolescents and adults

FREQUENCY Number of times fluid milk was consumed 1.65 0.81 

QUANTITY Total intake of fluid milk over 24 hours (cups) 1.48 0.71

INCOME Household income (per capita 2003 dollars) 10,893.84 18,282.27

AGE Age at the time of survey participation (years) 6.96 42.21

HHSIZE Number of people living in household 4.52 3.13

PREGNANT 1 for pregnant; 0 otherwise 0.01

DIETING 1 for on a special diet; 0 otherwise 0.07

HISPANIC 1 for Hispanic ethnicity; 0 otherwise 0.14 0.09

BLACK 1 for Black; 0 otherwise 0.15 0.11

MALE 1 for male; 0 otherwise 0.51 0.46

COLLEGE 1 if household head finished college; 0 otherwise 0.28 0.29

WEEKEND 1 if dietary recall for a weekend; 0 otherwise 0.25 0.26

C1 1 if born prior to 1930; 0 otherwise 0.17

C2 1 if born between 1930-1934; 0 otherwise 0.05

C3 1 if born between 1935-1939; 0 otherwise 0.05

C4 1 if born between 1940-1944; 0 otherwise 0.07

C5 1 if born between 1945-1949; 0 otherwise 0.08

C6 1 if born between 1950-1954; 0 otherwise 0.09

C7 1 if born between 1955-1959; 0 otherwise 0.10

C8 1 if born between 1960-1964; 0 otherwise 0.11

C9 1 if born between 1965-1969; 0 otherwise 0.07

C10 1 if born between 1970-1974; 0 otherwise 0.07

C11 1 if born between 1975-1979; 0 otherwise 0.06

C12 1 if born between 1980-1984; 0 otherwise 0.04

C13 1 if born between 1985-1989; 0 otherwise 0.03

C14 1 if born between 1990-1994; 0 otherwise 0.02

TIME1 1 if 1977-78 NFCS; 0 otherwise 0.17 0.16

TIME2 1 if 1989-91 CSFII; 0 otherwise 0.21 0.20

TIME3 1 if 1994-96 CSFII; 0 otherwise 0.37 0.35

TIME4 1 if 2003-04 NHANES; 0 otherwise 0.13 0.14

TIME5 1 if 2007-08 NHANES; 0 otherwise 0.13 0.15

Source: Calculated by the authors using the 1977-78 Nationwide Food Consumption Survey (NFCS), the 1989-1991 Continuing Survey of 

Food Intakes by Individuals (CSFII), the 1994-1996 CSFII, the 2003-04 National Health and Nutrition Examination Survey (NHANES), and the 

2007-08 NHANES and accompanying sample weights.
14 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

has been conducted on methods for specifying this type of model. In this study, 

ERS followed procedures outlined by Deaton (1997), Johnson (1980), and Stewart 

and Blisard (2008) for defining explanatory variables and identifying cohort effects. 

Previous studies have analyzed the effects of income, age, gender, race, ethnicity, 

and other demographic characteristics on fluid milk consumption. Based on Lin et 

al. (2003) and Davis et al. (2010), among other papers cited in this study, researchers 

defined several variables for inclusion in the model (table 2). These included the 

natural logarithm of a person’s age (AGE), which is consistent with research showing 

that fluid milk consumption tends to be stable in childhood, falls in adolescence, and 

continues to fall at a slower rate throughout adulthood (e.g., Lin et al., 2003; Mannino 

et al., 2004; Sebastian et al., 2010). The researchers also included the natural logarithms of a person’s household income (INCOME) and household size (HHSIZE), as 

well as binary variables for gender (MALE), race (BLACK), ethnicity (HISPANIC), 

whether at least one head of household has completed college (COLLEGE), and 

whether consumption was reported for a Saturday or Sunday (WEEKEND). For teenagers and adults, the researchers added binary variables to control for whether survey 

participants were dieting (DIETING) or pregnant (PREGNANT) during the 24 hours 

described in their 1-day dietary recall.

In addition to factors identified as important determinants of fluid milk consumption in past studies, researchers included explanatory variables for testing whether 

the number of times per day that a person consumes fluid milk varies across the 

generations. These binary explanatory variables include C2, for people born 1930-

34; C3, 1935-39; and so on in 5-year intervals, up to C14, 1990-94. By including 

C2 through C14 in the econometric model, the researchers could calculate the 

expected differences in consumption between each of these more recent cohorts and 

Americans born prior to 1930.10 Evidence that more recently born cohorts consume 

fluid milk less often than older cohorts would confirm that a cohort effect is contributing to declining consumption frequency. By contrast, finding no consistent variance of consumption frequency across generations would refute the hypothesis that 

cohort effects are part of the trend. 

ERS researchers also created binary variables that identify which USDA survey 

an individual joined. One of these binary variables, TIME2, indicates that an individual participated in the 1989-91 CSFII. Likewise, TIME3 identifies participants 

in the 1994-96 CSFII. And, finally, TIME4 and TIME5 denote participants in the 

2003-04 and the 2007-08 NHANES. The estimation results on these four variables 

compare participants in the 1977-78 NFCS with participants in each of the subsequent surveys, holding all other explanatory variables in the model constant.11

Unlike C2 through C14, which capture differences between the generations likely 

related to their experiences as children, TIME2 through TIME5 were hypothesized 

10Individuals born prior to 1930 would not have likely been influenced as preadolescent 

children by the changes in milk consumption that started in the 1940s. ERS researchers, 

therefore, hypothesized that generational effects exist only for Americans born in 1930 or 

more recently.

11For example, given that the other explanatory variables included a person’s income, 

demographic characteristics, and his or her birth year, ERS researchers could interpret the 

results on TIME5 to answer the question, “If the same population that existed in 1977-78 still 

existed in 2007-08, how much would consumption have fallen or risen?”
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 15

to capture the contemporaneous effects on all individuals of the availability of 

competing beverages and other aspects of the food marketing system. 

Finally, ERS created a variable to account for prices. Prices for fluid milk have 

tended to fluctuate relative to prices for other nonalcoholic beverages. The researchers 

divided the Consumer Price Index (CPI) for fresh whole milk by the CPI for all nonalcoholic beverages.12 The ratio of the two CPIs was 0.98 in 1977, 1.03 in 1989, 1.04 

in 1994, 1.16 in 2003, and 1.34 in 2007. Values greater than one indicate that the cost 

of fresh whole milk has increased faster than the cost of nonalcoholic beverages in 

general. However, the inclusion of the price variable in addition to TIME2 through 

TIME5 did not improve estimation results. The likely reason is that, as compared 

with data in a typical time series study, the available data showed the food choices 

of Americans at only a small number of different price levels. Although the USDA 

dietary surveys pooled for this study collectively span over 30 years, data were available only for the years in which one of the five surveys was administered. Thus, the 

price variable was excluded from the final model.

Model Specification

How many times per day will an individual consume fluid milk products? 

The dependent variable FREQUENCY takes on only integer values: zero for 

nonconsumers, 1 for single occasion consumers, 2 for those who consumed on 

two occasions, and so on. Econometric models optimized for analyzing this type 

of data include the Poisson and negative binomial regression models. Greene 

(1997) provides a technical overview of each. Dong et al. (2000) used these 

models to study the number of times individuals patronize a restaurant. He et al. 

(2004) used the negative binomial model to analyze the number of times people 

consume beef, poultry, and seafood. In this study, ERS researchers assumed that 

the number of times a person drinks fluid milk could be approximated by the 

outcome of a Poisson distribution. By this model, the predicted value (conditional 

mean) of FREQUENCY is λ = eβX where e is the base of the natural logarithm, X 

is a set of explanatory variables, and β includes the parameters that describe the 

relationship between the dependent and explanatory variables by their sign (+/-) 

and magnitude. The researchers included in X a person’s income, demographic 

characteristics, decade of birth, and survey year. Of course, the number of times that 

a particular individual consumes fluid milk may vary from the predicted value on 

any given day. The Poisson regression model assumes that the mean and variance of 

FREQUENCY conditional on X are the same. Both equal λ. However, the closely 

related negative binomial regression model relaxes this assumption. It instead 

assumes that FREQUENCY has conditional mean λ and conditional variance 

λ(1 + (1/θ)λ) where 1/θ is an “overdispersion” parameter. Thus, the conditional 

variance of FREQUENCY may exceed its conditional mean because of either 

heterogeneity across survey participants or omission from the regression model of 

demand determinants for which the necessary data do not exist to explicitly create 

explanatory variables. Researchers who work with count data will commonly 

12The Bureau of Labor Statistics (BLS) has been publishing a CPI for whole fresh milk 

since at least the 1970s and a CPI for fresh milk other than whole milk since 1997. The two 

series have moved together closely. Changes in the two CPIs share a correlation coefficient 

of 0.98 in the years for which both indices are available. 
16 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

estimate both a Poisson and negative binomial model. They then select between the 

two specifications by conducting a test for overdispersion. 

The model further adds a second equation to the basic count data model for a 

survey participant’s total daily intake of fluid milk over all consumption occasions. 

The value of QUANTITY is zero if FREQUENCY equals zero (i.e., for consumers 

who drank no milk). For other consumers, QUANTITY = αZ, where Z is a set of 

explanatory variables and α contains the parameters that describe the relationship 

among the variables. Researchers hypothesized that QUANTITY depends partly on 

the number of times a person consumed fluid milk. Thus, FREQUENCY is included 

in Z, along with the demographic characteristics of an individual that may influence portion sizes, such as his or her gender and age. Finally, the four survey date 

variables are included in Z. If the parameters on TIME2 through TIME5 are found 

to be negative and increasingly large in magnitude from older to newer surveys, 

then that would suggest that portion sizes have tended to decrease since the 1970s. 

Otherwise, it can be concluded that changing portion sizes have not contributed 

much to the decline in fluid milk consumption shown in figures 1 and 2.

The two-equation model in this study is a triangular system. FREQUENCY 

is modeled in the first equation and, in turn, helps to determine the value of 

QUANTITY in the second equation. However, in this type of model, biased estimates of the relationship between FREQUENCY and QUANTITY may result if 

FREQUENCY is simply included among the other explanatory variables in Z in 

our second equation.13 To mitigate this problem, ERS researchers instead included 

the number of times per day that an individual is predicted to consume fluid milk, 

λ=eβX, in Z.14 

The researchers also allowed for the possibility that different factors may influence the food choices of preadolescent children and Americans age 13 and 

older. The two-equation model is estimated separately for people in these two 

age groups. Excluded from the model for preadolescent children are C2 through 

C14, PREGNANT, and DIETING. C2 through C14 are excluded from this model 

because it is customary to assume that young children are free of any habits associated with their year of birth (e.g., Mori and Saegusa, 2010); rather, they are still 

forming the habits that will later define their generation. 

Estimation of the model in the present study makes a novel contribution to research 

on fluid milk consumption and the broader body of research on food demand. In 

contrast to previous studies of milk demand like Lin et al. (2003) and Davis et 

al. (2010) that use cross-sectional data, this study instead pools surveys collected 

over 30 years. Moreover, to the authors’ knowledge, this study represents the first 

application of count models to pooled survey data for testing whether generational 

change contributes to trends in the consumption of any food commodity. Additional 

information on the model, including the complete likelihood function, is provided 

in Appendix II: Model Specification and Estimation. 

13Unobservable differences in tastes, dietary knowledge, and medical conditions between 

individuals could contribute to the error terms in both our equations for FREQUENCY and 

QUANTITY. That is, these omitted variables could affect both the frequency of consumption 

and portion sizes. This would then lead to endogeneity bias. 

14This is an instrumental variable approach.
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 17

Estimating the Model and Examining Results

Using data from the pooled USDA food consumption surveys, researchers estimated 

both the model for preadolescent children and the model for Americans beyond their 

preadolescent years by weighted maximum likelihood.15 As a preliminary exercise, 

the researchers initially estimated only the first equation for FREQUENCY as a 

standalone model. Poisson and negative binomial specifications were both considered. The researchers then used tests for overdispersion to select between these two 

specifications. Based on these test results, the researchers selected a Poisson model 

for preadolescent children and a negative binomial model for teenagers and adults.16 

The complete models, including the second equation for QUANTITY, were then 

estimated. The standard errors of ˆ

β α and ˆ were calculated using a bootstrap procedure.17 Lastly, ERS researchers confirmed the robustness of their key results.18 The 

results of model estimation are reported in table 3 and table 4. As a supplementary 

exercise, the researchers used these results to predict how a change in each of the 

birth year (C2 through C14) and time variables (TIME2 through TIME5) would 

affect the number of times per day that a person consumes fluid milk products 

(FREQUENCY).19 These marginal effects are shown in figures 7 and 8.

Generational Change Contributing to Decreases in 

Frequency of Consumption 

The results confirm that newer generations of Americans are consuming fluid milk 

products fewer times per day. For adolescents and adults, the marginal effects of the 

birth year variables represent the expected differences in consumption between a 

person born before 1930 and one born more recently, all else constant. For example, 

Americans born in the early 1960s are expected to consume fluid milk on about 1.1 

fewer occasions per day at age 20, age 30, and so on than Americans born before 

1930 consume at each of these same ages. This marginal effect is calculated using 

the estimation results for C8 (fig. 7). Moreover, Americans born in the early 1980s 

15Sample weights provided by USDA for use with its surveys were incorporated into the 

estimation.

16Consistent with test results for adolescents and adults, ERS researchers noted that the 

mean of FREQUENCY (0.81) was less than the variance of FREQUENCY (1.01). This was 

not the case for preadolescent children. FREQUENCY had a mean and variance of 1.65 and 

1.43 among survey respondents in this age group, respectively. 

17Efron and Tibshirani (1998, p. 52) report that 100 replications “gives quite satisfactory 

results” and “very seldom” are more than 200 replications needed. For this study, ERS 

researchers used 250 replications. Each replication included 64,192 observations drawn from 

the original sample with replacement and a probability proportional to the sample weight 

(Efron and Tibshirani, 1998; Lee and Forthofer, 2006).

18For example, ERS checked that the findings on C2 through C14 for adolescents and 

adults were not driven by any correlation with changes in prices, changes in the availabilities 

of milk and competing beverages, or changes in other factors correlated with time. This was 

accomplished by re-estimating the equation for FREQUENCY for adolescents and adults 

excluding all time variables, TIME2 through TIME5. Estimation results on C2 through C14 

were qualitatively unchanged, confirming the robustness of our findings.

19ERS estimated these effects for each individual in the sample. They then used the 

sample weights to calculate the weighted averaged effect across all individuals. See also 

notes to figures 7 and 8.
18 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Table 3

Frequency and quantity of fluid milk consumption, coefficient estimates for adolescents 

and adults

FREQUENCY QUANTITY

Coefficient Std. Error Coefficient Std. Error

Birth year (generation) variables

C2 -0.31* 0.03

C3 -0.48* 0.03

C4 -0.60* 0.03

C5 -0.64* 0.04

C6 -0.82* 0.04

C7 -0.92* 0.04

C8 -0.90* 0.05

C9 -1.21* 0.05

C10 -1.28* 0.06

C11 -1.30* 0.07

C12 -1.35* 0.08

C13 -1.47* 0.09

C14 -1.42* 0.10

Time (survey) variables 

TIME2 0.04 0.02 0.05 0.03

TIME3 0.04 0.02 0.04 0.03

TIME4 0.05 0.03 0.27* 0.04

TIME5 0.10* 0.04 0.10 0.04

Income and demographic variables

ln(INCOME) -0.03* 0.01 -0.02* 0.01

ln(AGE) -0.70* 0.04 -0.52* 0.02

ln(HHS) 0.04* 0.01

MALE 0.05* 0.01 0.39* 0.01

WEEKEND -0.12* 0.01

COLLEGE 0.09* 0.01 -0.05* 0.02

PREGNANT 0.44* 0.04 0.39* 0.06

DIETING -0.04 0.02 -0.07 0.03

BLACK -0.55* 0.02 -0.14* 0.03

HISPANIC -0.04 0.02 -0.19* 0.02

Other model parameters

CONSTANT 3.27* 0.18 3.13* 0.11

1/θ 0.22* 0.01

λ 0.17* 0.06

* = significant at the 1-percent level

Source: Model estimated by ERS researchers using weighted maximum likelihood, sample weights provided by data in the 

1977-78 Nationwide Food Consumption Survey (NFCS), the 1989-1991 Continuing Survey of Food Intakes by Individuals 

(CSFII), the 1994-1996 CSFII, the 2003-04 National Health and Nutrition Examination Survey (NHANES), and the 2007-08 

NHANES. Standard error of equation for QUANTITY was 1.2. 
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 19

are expected to consume fluid milk on about 0.3 occasions less per day than those 

born in the early 1960s. This finding follows from the estimation result for C8 

and C12 and is also depicted in figure 7. Such large decreases in the frequency of 

consumption between individuals born several decades apart could gradually reduce 

per capita consumption as successively newer generations slowly replace older 

generations and account for a steadily larger share of the overall population. 

If there were no cohort effect and the other explanatory variables in the model had 

remained unchanged, American adolescents and adults would have likely maintained the frequency of their fluid milk consumption from the 1970s into the 2000s. 

This conclusion follows from the marginal effects of TIME2 through TIME5 (fig. 

8). As discussed above, these variables are hypothesized to capture the contemporaneous effects of the food marketing system such as the availability of competing 

beverages. For adolescents and adults, these effects are small and do not tend 

to increase or decrease in magnitude from the older to more recent USDA food 

consumption surveys. Once people are past childhood, their food choices seem to 

be much more influenced by their childhood-formed habits than by changes over 

their life times in the environment in which their food choices are made. 

Table 4

Frequency and quantity of fluid milk consumption, coefficient estimates for preadolescent 

children

FREQUENCY QUANTITY

Coefficient Std. Error Coefficient Std. Error

Time (survey) variables

TIME2 -0.10* 0.02 0.00 0.04

TIME3 -0.16* 0.02 -0.10* 0.04

TIME4 -0.19* 0.03 0.03 0.05

TIME5 -0.25* 0.02 -0.22* 0.05

Income and Demographic variables

ln(INCOME) -0.04* 0.01 -0.02 0.01

ln(AGE) -0.19* 0.01 0.18* 0.03

ln(HHS) 0.02 0.03

MALE 0.05* 0.01 0.19* 0.02

WEEKEND -0.22* 0.02

COLLEGE 0.08* 0.02 0.01 0.03

BLACK -0.32* 0.02 -0.19* 0.05

HISPANIC -0.01 0.02 0.06 0.03

Other model parameters

CONSTANT 1.37* 0.11 1.18* 0.27

 λ 0.30* 0.08

* = significant at the 1-percent level

Source: Model estimated by ERS researchers using weighted maximum likelihood, sample weights provided by data 

in the 1977-78 Nationwide Food Consumption Survey (NFCS), the 1989-1991 Continuing Survey of Food Intakes by 

Individuals (CSFII), the 1994-1996 CSFII, the 2003-04 National Health and Nutrition Examination Survey (NHANES), and 

the 2007-08 NHANES. Standard error of equation for QUANTITY was 1.12. 
20 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

However, changes over time in the food environment—that is, trends in prices, mix 

of competing products, etc.—appear responsible for reducing children’s fluid milk 

consumption. As also shown in figure 8, these effects are increasingly negative 

from the older to the newer surveys for preadolescent children. We find that preadolescent children tended to drink milk on 0.28 fewer occasions per day in 1994-96 

than did preadolescent children in 1977-78, all else constant. By 2007-08, they were 

consuming it on 0.42 fewer occasions per day than in 1977-78. 

Finally, the estimation results for household income and demographic variables 

generally agree with past studies. As shown in table 3, Americans drink milk fewer 

times per day as they age. They also consume it more frequently if at least one head 

of household has completed college. From these results and the findings of existing 

studies, it follows that economic and demographic changes in the Nation’s population are enhancing or mitigating the declining frequency of fluid milk consumption. 

For example, more Americans are completing college (Cromartie, 2002). The median 

age of the U.S. population has also increased from 28.1 years in 1970 to 32.9 years in 

1990, and 37.2 years in 2010 (Hobbs and Stoops, 2002; Howden and Meyer, 2011). 
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 21

Portions Remaining Largely Stable

Changes in portions over time appear to contribute little to trends in fluid milk 

consumption. For both preadolescent children and Americans age 13 and older, 

estimates of the parameters in the model’s second equation reveal a positive relationship between FREQUENCY and QUANTITY. Americans who consume fluid 

milk on more occasions per day tend to consume a larger quantity overall. However, 

ERS researchers obtained negative, positive, and zero values for the parameters on 

TIME2 through TIME5 in the same second equation. Thus, there is no evidence of 

a trend in quantities consumed after accounting for the other variables in the second 

equation of the model. This result is consistent with the earlier discussions of figures 

4 and 5. It again suggests that portions have changed relatively little and, therefore, 

that changes over time in QUANTITY reflect primarily changes in FREQUENCY. 
22 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Considering the Health Implications of Trends in Milk 

Consumption 

Americans are consuming less fluid milk, on average, because they drink it on fewer 

occasions per day. In particular, they drink it less often with their midday and nighttime meals. Mitigating the decline are programs supported by dairy farmers, fluid 

milk processors, and the Federal Government. Kaiser (2010) confirms that promotions sponsored by checkoff programs increase the demand for fluid milk. Gleason 

and Suitor (2001) similarly identify a positive association between children’s participation in the NSLP and their consumption of fluid milk. These programs moderated 

the decline in U.S. per capita fluid milk consumption between the 1970s and the 

2000s. However, because greater decreases in consumption frequency are observed 

among more recent generations of Americans, it may be difficult to reverse ongoing 

consumption trends. Indeed, holding all other factors constant, the gradual replacement in the population of older generations by newer generations will exert downward pressure on Americans’ average consumption of fluid milk.

Sustained decreases in per capita fluid milk consumption would work against efforts 

to raise Americans’ overall dairy consumption to recommended levels. To date, 

Americans have merely maintained their total intake of dairy products by consuming 

more Cheddar cheese and more mozzarella cheese (USDA-ERS, 2013a). However, 

the Nation’s population would be closer to satisfying dairy recommendations in the 

Dietary Guidelines for Americans, 2010 if Americans were still drinking as much 

fluid milk as they did in the 1970s, in addition to the amounts of other dairy products 

they now consume.20 Additionally, cheese products can contain as many or more 

calories than fluid milk. On a per cup-equivalent basis,21 regular Cheddar cheese 

(171 calories) has more calories than a glass of whole milk (149 calories). Whole-fat 

mozzarella (128 calories) has slightly more calories than 2 percent milk (122 calories). 

Part-skim mozzarella (108 calories) has slightly more calories than 1 percent milk 

(102 calories) and somewhat more than skim milk (86 calories).

Nutrition and health policy researchers have warned of the potential health implications of declining fluid milk consumption (e.g., Cavadini et al. 2000; Popkin 2010). 

If fluid milk consumption continues to decline in response to cohort effects, then 

raising Americans’ dairy intakes and improving overall diet quality would require 

substantially greater increases in the consumption of non-fluid products in skim 

and low-fat form. Maintaining a focus on children may also be key to mitigating 

or halting the downward trend in fluid milk consumption, because habit formation 

implies that childhood food choices can affect longrun behavior.

20ERS food availability data show that Americans consume 1.53 cup-equivalents of dairy 

products, on average, including 0.61 cup-equivalents of fluid milk (USDA-ERS, 2013a). Thus, 

raising fluid milk consumption to 0.96 cup-equivalents per person, as in the early 1970s, 

would raise the per capita total to about 2 cup-equivalents. As noted above, The Dietary 

Guidelines for Americans, 2010 recommends 2 cup-equivalents per day for children aged 2 to 

3 years, 2.5 for those aged 4 to 8 years, and 3 for Americans older than age 8. 

21Consuming 8 ounces of fluid milk, 1.5 ounces of Cheddar cheese, or 1.5 ounces of 

mozzarella cheese all count equally toward an individual’s consumption of dairy products. 

Each is considered to be 1 cup-equivalent. Each is also available in higher and lower fat 

forms. ERS researchers used the USDA National Nutrient Database for Standard Reference, 

Release 25 (USDA, Agricultural Research Service, 2013b) to compare the number of calories 

in selected forms of these foods’ per cup-equivalents.
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 23

References

Bowman, S., S. Gortmaker, C. Ebbeling, M. Pereira, and D. Ludwig. 2004. “Effects of 

Fast-Food Consumption on Energy Intake and Diet Quality Among Children in a 

National Household Survey,” Pediatrics, Vol. 113: pp. 112-118.

Cavadini C., A. Siega-Riz, and B. Popkin. 2000. “U.S. adolescent food intake trends 

from 1965 to 1996,” Archives of Disease in Childhood, Vol. 83: pp. 18–24.

Conway J., L. Ingwersen, and A. Moshfegh. 2004. “Accuracy of Dietary Recall Using 

the USDA Five-Step Multiple-Pass Method in Men: An Observational Validation 

Study,” Journal of the American Dietetic Association, Vol. 104: pp. 595-603.

Cromartie J. 2002. “Population Growth and Demographic Change, 1980-2020,” 

FoodReview, Vol. 25(1): pp. 10-12. Available at http://www.ers.usda.gov/publications/FoodReview/May2002/DBGen.htm.

Davis C., D. Dong, D. Blayney, and A. Owens. 2010. An Analysis of U.S. Household 

Dairy Demand, TB-1928, U.S. Department of Agriculture, Economic Research 

Service. Available at http://www.ers.usda.gov/publications/tb1928/tb1928.pdf .

Deaton A. 1997. The Analysis of Household Surveys: A Microeconometric Approach to 

Development Policy. Baltimore: The Johns Hopkins University Press.

Dong D., P. Byrne, A. Saha, and O. Capps. 2000. “Determinants of Food-Away-FromHome (FAFH) Visit Frequency: A Count-Data Approach,” Journal of Restaurant & 

Foodservice Marketing, Vol. 4(1): pp. 31-46.

Efron B., and R. Tibshirani. 1998. An Introduction to the Bootstrap. New York: 

Chapman & Hall.

Enns C., J. Goldman, and A. Cook. 1997. “Trends in Food and Nutrient Intakes by 

Adults: NFCS 1977-78, CSFII 1989-91, and CSFII 1994-95,” Family Economics 

and Nutrition Review, Vol. 10(4): pp. 2-15.

Fisher J., D. Mitchell, H. Smiciklas-Wright, and L. Birch. 2001. “Maternal Milk 

Consumption Predicts the Tradeoff Between Milk and Soft Drinks in Young Girls’ 

Diets,” Journal of Nutrition, Vol. 131(2): pp. 246-250.

Gleason P., and C. Suitor. 2001. Children’s Diets in the Mid-1990s: Dietary Intake and 

Its Relationship with School Meal Participation, Special Nutrition Programs Report 

No. CN-01-CD1, U.S. Department of Agriculture, Food and Nutrition Service. 

Available at http://www.fns.usda.gov/ora/menu/published/CNP/FILES/ChilDiet.pdf

Greene W. 1997. Econometric Analysis, 3rd ed., New Jersey: Prentice Hall.

He S., S. Fletcher, and A. Rimal. 2004. “Identifying Factors Influencing Beef, Poultry, 

and Seafood Consumption,” Journal of Food Distribution Research, Vol. 34(1): pp. 

50-55.
24 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Hobbs F., and N. Stoops. 2002. Demographic Trends in the 20th Century, Census 2000 

Special Reports, Series CENSR-4, U.S. Department of Commerce, Census Bureau. 

Available at http://www.census.gov/prod/2002pubs/censr-4.pdf

Howden L., and J. Meyer. 2011. Age and Sex Composition: 2010, C2010BR-03, U.S. 

Department of Commerce, Census Bureau. Available at http://www.census.gov/

prod/cen2010/briefs/c2010br-03.pdf

Johnson W. 1980. “Vintage Effects in the Earnings of White American Men,” The 

Review of Economics and Statistics, Vol. 62(3): pp. 399-407.

Kaiser H. 2010. Measuring the Impacts of Generic Fluid Milk and Dairy Marketing, 

Research Bulletin 2010-01, Cornell University, National Institute for Commodity 

Promotion & Research Evaluation. Available at http://dyson.cornell.edu/research/

researchpdf/rb/2010/Cornell_Dyson_rb1001.pdf.

Kaiser, H., and D. Dong. 2006. Measuring the Impacts of Generic Fluid Milk and 

Dairy Marketing, Research Bulletin 2006-05, Cornell University, National Institute 

for Commodity Promotion & Research Evaluation. Available at http://commodity.

dyson.cornell.edu/nicpre/bulletins/rb0605/rb2006_05.pdf

Lee, E., and R. Forthofer. 2006. Analyzing Complex Survey Data, 2nd. ed. Thousand 

Oaks, California: Sage Publications.

Lin B-H, J. Variyam, J. Allshouse, and J. Cromartie. 2003. Food and Agricultural 

Commodity Consumption in the United States: Looking Ahead to 2020, AER-820, 

U.S. Department of Agriculture, Economic Research Service. Available at http://

www.ers.usda.gov/Publications/AER820/ .

Mannino M., Y. Lee, D. Mitchell, H. Smiciklas-Wright, and L. Birch. 2004. 

“The Quality of Girls’ Diets Declines and Tracks Across Middle Childhood,” 

International Journal of Behavioral Nutrition and Physical Activity, Vol. 1(5). 

Mori H., D. Clason, and J. Lillywhite. 2006. “Estimating Price and Income Elasticities 

in the Presence of Age-Cohort Effects,” Agribusiness: An International Journal, 

Vol. 22(2): pp. 201-217.

Mori H., and Y. Saegusa. 2010. “Cohort Effects in Food Consumption: What They Are 

and How They Are Formed,” Evolutionary and Institutional Economics Review, 

Vol. 7(1): pp. 43–63.

Mori, H., and H. Stewart. 2011. “Cohort Analysis: Ability to Predict Future 

Consumption – The Cases of Fresh Fruit in Japan and Rice in Korea,” The Annual 

Bulletin of Social Science, Vol. 45: pp. 153-173.

Moshfegh A., D. Rhodes, D. Baer, T. Murayi, J. Clemens, W. Rumpler, D. Paul, R. 

Sebastian, K. Kuczynski, L. Ingwersen, R. Staples, and L. Cleveland. 2008. “The 

US Department of Agriculture Automated Multiple-Pass Method Reduces Bias in 

the Collection of Energy Intakes,” American Journal of Clinical Nutrition, Vol. 88: 

pp. 324-32.
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 25

National Dairy Promotion and Research Board. 2013. Dairy Checkoff Programs. 

Available at http://www.dairycheckoff.com

Popkin, B. 2010. “Patterns of Beverage Use Across the Lifecycle,” Physiology & 

Behavior Vol. 100(1): pp. 4-9.

Schrimper, R. 1979. “Demographic Changes and the Demand for Food: Discussion,” 

American Journal of Agricultural Economics 61(5): pp. 1058-60.

Sebastian, R., J. Goldman, C. Enns, and R. LaComb. 2010. “Fluid Milk Consumption 

in the United States: What We Eat In America, NHANES 2005-2006.” 2010. Food 

Surveys Research Group Dietary Data Brief. No. 3, U.S. Department of Agriculture, 

Agricultural Research Service. Available at http://ars.usda.gov/SP2UserFiles/

Place/12355000/pdf/DBrief/fluid_milk_0506.pdf

Stewart, H., D. Dong, and A. Carlson. 2012. “Is generational change contributing 

to the decline in fluid milk consumption?” Journal of Agricultural and Resource 

Economics Vol. 37(3): pp. 435-54.

Stewart H., and N. Blisard. 2008. “Are Younger Cohorts Demanding Less Fresh 

Vegetables?” Review of Agricultural Economics, Vol. 30(1): pp. 43-60.

Tippett K., and Y. Cypel. 1997. Design and Operation: The Continuing Survey of Food 

Intakes by Individuals and the Diet and Health Knowledge Survey, 1994–96, NFS 

Report No. 96-1, U.S. Department of Agriculture, Agricultural Research Service. 

Available at http://www.ars.usda.gov/sp2userfiles/place/12355000/pdf/Dor9496.pdf.

U.S. Department of Agriculture, Agricultural Research Service. 2013a. Food and 

Nutrient Database for Dietary Studies. Available at http://www.ars.usda.gov/

Services/docs.htm?docid=12089

U.S. Department of Agriculture, Agricultural Research Service. 2013b. National 

Nutrient Database for Standard Reference (Release 25). Available at http://www.

ars.usda.gov/. 

U.S. Department of Agriculture, Agricultural Research Service. 2013c. USDA 

Food Surveys, 1935-1998. Available at http://www.ars.usda.gov/Services/docs.

htm?docid=14392 . 

U.S. Department of Agriculture, Agricultural Research Service. 2013d. What We Eat 

in America. Available at http://www.ars.usda.gov/Services/docs.htm?docid=13793. 

U.S. Department of Agriculture, Economic Research Service. 2013a. Loss-Adjusted 

Food Availability. Available at http://www.ers.usda.gov/Data/FoodConsumption/

FoodGuideIndex.htm/.

U.S. Department of Agriculture, Economic Research Service. 2013b. Food 

Availability (Per Capita) Data System. Available at http://www.ers.usda.gov/Data/

FoodConsumption/

 U.S. Department of Agriculture and U.S. Department of Health and Human Services. 

2010. Dietary Guidelines for Americans, 2010 7th ed. Washington, DC, December. 

Available at http://www.cnpp.usda.gov/dietaryguidelines.htm
26 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Appendix I: Comparing Consumption Across Different 

USDA Dietary Intake Surveys

USDA has been surveying individuals about their dietary intake for several decades. 

A history of these surveys is available online.22 The 1977-78 Nationwide Food 

Consumption Survey (NFCS) was USDA’s first survey to be administered nationwide, to cover all four seasons of the year, and to record the food and beverage 

intakes of a large number of individuals. Subsequent surveys include the 1989-1991 

Continuing Survey of Food Intakes by Individuals (CSFII) and the 1994-1996 

CSFII. In 2002, the dietary recall portion of the CSFII was integrated with the 

National Health and Nutrition Examination Survey (NHANES), which is administered by the U.S. Department of Health and Human Services (DHHS). USDA and 

DHHS now release the results of their integrated survey every 2 years. All of these 

USDA surveys are nationally representative when analyzed using sample weights. 

Pooling food consumption surveys collected intermittently over time is complicated 

by changes in USDA’s survey methodology. For example, in the 1977-78 NFCS 

and the 1989-91 CSFII, USDA interviewed individuals to complete a 1-day dietary 

recall for the previous day.23 Participants then self-reported their own intakes over 

the subsequent two days (a 2-day diary). By contrast, starting with the 1994-96 

CSFII, USDA has interviewed individuals twice to obtain two 1-day dietary recalls 

for nonconsecutive days. The NHANES continues to collect multiple 1-day dietary 

recalls as did the 1994-96 CSFII. 

USDA has been consistently administering 1-day dietary recalls for more than 

30 years, notwithstanding other changes in survey methodology. It is, therefore, 

possible to study long-run trends in the American diet by pooling data from only 

that component of different surveys. Enns et al. (1997) used the 1977-78 NFCS 

and both CSFIIs to study food consumption trends between the late 1970s and 

the late 1990s. Cavadini et al. (2000) used these same surveys to focus on dietary 

trends among American adolescents. Both studies used only the day 1 dietary recall 

collected shortly after the start of each survey. “This method avoids the biasing 

of intake results that may occur because of the different dietary data collection 

methods used ...” (Cavadini et al., 2000, p. 18-19). 

USDA has also been improving its protocol for dietary recall interviews since the 

initial surveys. Research conducted after the 1989-91 CSFII confirmed that survey 

participants were having difficulty recalling all the foods and beverages consumed 

the previous day. To aid their memory and reduce the potential for underreporting 

food intakes, USDA developed a “multiple-pass” protocol. Beginning with the 

1994-96 CSFII, interviewers first instructed participants to report all foods and 

beverages consumed the previous day from midnight to midnight. Then, in a second 

pass, they asked questions about food items that participants may commonly forget 

(including, for example, milk on cereal). Finally, in a third pass, interviewers asked 

22See USDA, Agricultural Research Service (2013c, 2013d).

23In the 1977-78 NFCS, USDA also collected information on household food use over a 

1-week period. In the 1989-91 CSFII, USDA ceased to collect household food use data and 

concentrated exclusively on the diets of individuals.
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 27

questions about eating occasions that survey participants commonly forget. For 

example, they would ask questions like “Did you nibble or sip on anything while 

preparing a meal or while waiting to eat that you haven’t already told me about?” 

(see, for example, Tippett and Cypel, 1997). After the merger of the CSFII and 

NHANES surveys, USDA’s three-step methodology was extended to five steps. 

Studies continue to evaluate the accuracy of dietary recall data collected using the 

latest multiple-pass protocol (e.g., Conway et al., 2004; Moshfegh et al., 2008). 

Because of the introduction of USDA’s multiple-pass protocol, it is possible that 

participants in earlier surveys were more likely to underreport fluid milk consumption than participants in later surveys, though the size of any bias remains unknown. 

However, figures 1 and 2 reveal that estimates of per capita fluid milk consumption reported in ERS loss-adjusted food availability data are similar to estimates 

of per capita consumption based on the five USDA food consumption surveys for 

Americans of all ages. For example, both sources report that Americans, on average, 

consumed about 1 cup of fluid milk per day in 1977-78 and about 0.7 cups per day in 

2007-08. ERS researchers, therefore, expect that any bias in reported consumption of 

fluid milk due to the evolution of USDA’s multiple-pass protocol is small.

In the current study, ERS researchers focused on fluid milk consumption by participants in USDA surveys over 24 hours. As noted in the text, the researchers included 

both plain and flavored products consumed alone as a beverage, put in cereal, 

poured in coffee, or used as an ingredient in selected coffee drinks. USDA dietary 

records report fluid milk consumption in grams. These quantities were converted 

into fluid ounces (8 fluid ounces = 1 cup). Quantities of milk consumption were 

converted from weight to volume by using the USDA National Nutrient Database 

for Standard Reference, Release 25 (USDA, Agricultural Research Service, 2013b). 

One 8-ounce cup weighs about 244 grams. The final data set includes information on 64,192 individuals excluding people who failed to provide a reliable day 1 

dietary recall, did not provide complete household income or demographic information, or were young children and still breast-feeding. 
28 Why Are Americans Consuming Less Fluid Milk? ERR-149 Economic Research Service, USDA

Appendix II: Model Specification and Estimation

The Poisson and negative binomial regression models are widely used to analyze 

count data. In this study, ERS researchers investigated the number of times per 

day that a person consumes fluid milk (FREQUENCY) and tested whether generational change is contributing to long-run trends in that number. ERS researchers 

also augmented the basic count data model with a second equation that predicts a 

survey participant’s overall intake of fluid milk (QUANTITY). The goal in adding 

this second equation was to confirm or refute the possibility that changes in portions 

sizes are also contributing to trends in fluid milk consumption. 

The primary dependent variable in our study, FREQUENCY, can only equal 

zero or a positive integer value. The probability that it equals a particular value, 

0,1,2,3,...,∞, using the negative binomial regression model, is:

f(FREQUENCY|X) = 

FREQUENCY (FREQUENCY )

(1 FREQUENCY) ( )

θ

Γ +θ θ λ       Γ + Γ θ θ+λ θ+λ   

where λ = eβX is the conditional mean of FREQUENCY, X is a set of explanatory 

variables, β is a vector of parameters, e is the base of the natural logarithm, Γ(·) 

is the gamma function, and 1/θ is the overdispersion parameter. As discussed in 

the text, if there is no overdispersion, then θ approaches infinity, the conditional 

mean and variance of FREQUENCY become equal, and the negative binomial and 

Poisson regression models become identical. 

Among survey participants who consumed fluid milk on zero occasions, both 

FREQUENCY and QUANTITY equal zero. This occurs with probability 

P(FREQUENCY=0) = ( )

(1) ( )

θ

Γθ θ     Γ Γ θ θ+λ   .

For other survey participants, FREQUENCY and QUANTITY are outcomes of the 

two variables’ joint probability distribution:

h(FREQUENCY,QUANTITY|X,Z) = g(QUANTITY| Z)·f(FREQUENCY|X)

where f(FREQUENCY|X) is above and g(QUANTITY| Z) is the distribution of 

QUANTITY conditional on Z. We assume that 

g(QUANTITY| Z) = 

2 1 QUANTITY Z 1 2 e

2

  −α −     σ

πσ

where α is a vector of parameters, e is the base of the natural logarithm, and Z is a 

set of explanatory variables. That is, we assume g(·) is a normal distribution with 

mean αZ and variance σ2. As discussed in the text, we include FREQUENCY 

among the variables in Z, but use λ=eβX for estimation purposes to reduce the potential for endogeneity bias.
Economic Research Service, USDA Why Are Americans Consuming Less Fluid Milk? ERR-149 29

Participants in USDA food consumption surveys must belong to one of two 

regimes. As noted above, if an individual reported consuming no fluid milk, then 

both FREQUENCY and QUANTITY equal zero. The contribution to the likelihood 

function of these individuals follows from the probability of this event as shown 

above:

L1(β) = ( )

(1) ( )

θ

Γθ θ     Γ Γ θ θ+λ   .

For survey participants who consumed fluid milk one or more times, the contribution to the likelihood function is

L2(α,β) = 

Finally, the weighted likelihood function for the full sample of i=1,...,N individuals 

is :

L(α,β) = N wi ∏i=1 i L

where wi

 is the sample weight for individual i, Li equals L1 if FREQUENCYi = 0, 

and Li

 equals L2 if FREQUENCYi > 0. Estimates of model parameters α and β can 

be obtained by maximizing the weighted log-likelihood,

lnL(α,β) = N ∑i=1i i w lnL . 

2 1 QUANTITY Z FREQUENCY 1 2 (FREQUENCY ) e

2 (1 FREQUENCY) ( )

  −α θ −     σ Γ +θ θ λ      

πσ Γ + Γ θ θ+λ θ+λ   