What we need to know about teen food habits and why.

There is virtually no debate anymore about the seriousness of the obesity epidemic and the need for effective obesity prevention efforts starting early in life. For many years to come, food and nutrition professionals can expect to use their expertise in guiding strategies or evaluating programs to promote optimal child growth, nutrition, and health, while preventing obesity. In a 2005 report, the Institute of Medicine (IOM) Committee on Prevention of Obesity in Children and Youth presented its action plan for preventing childhood obesity at the family, school, community, industry, media, and government levels (1). The committee pointed out that obesity prevention in children is very complex and requires consideration of the foods and beverages young people are consuming over time, along with the factors that influence their food-related and physical-activity‐related decisions. In a subsequent report, the IOM emphasized the importance of including evaluation as an essential component of programs aimed at childhood obesity prevention (2). A review of recent educational interventions for preventing childhood obesity concluded that most have had minimal impact on weight status, although nearly all have improved diet or physical activity (3). Of 22 studies reviewed in the article, more than half were short term and many failed to describe the community context or economic conditions that may have influenced the outcomes. Stronger evaluation, including a better understanding of the environmental context, is needed to inform local, state, and federal efforts to prevent childhood obesity. LINKING DIETARY INTAKE TO OBESITY CAN BE DIFFICULT Although the severity of childhood obesity as a threat to public health is clear, identifying how dietary intake and obesity are related is more controversial (4). Cross-sectional studies in overweight and normal-weight children often have failed to show that total energy intake or macronutrient consumption is related to body fatness. A number of methodological reasons could explain these results. For instance, overweight children may underreport their intake, compared with normal-weight children, or they may already be on a diet for weight control based on family or health advice. Thus, their body weight reflects more closely what they ate in the past rather than the present. To understand how dietary factors are related to body fatness, we may need more longitudinal studies beginning in children before they become overweight. However, in several longitudinal studies the results have not always shown a relationship between total energy or macronutrient intake and onset of obesity (5-7). Before jumping to the conclusion that diet doesn’t matter (or possibly that physical activity is more important), we need to acknowledge that longitudinal studies of dietary intake and weight gain have their limitations as well. Small studies may lack the power to detect differences among subjects who can be consistently classified as having high or low intakes (7). Another important question to ask is whether those who remain in the cohort are more motivated or different in some other way than the “lostto-follow-up” group. Good description of the sample and the context can help in interpreting the findings.