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Nutrition and Military Performance

Chapter 6

NUTRITION AND MILITARY 

PERFORMANCE

DANIELLE S. DAY, PhD*; ANDREW YOUNG, PhD†; and ELDON W. ASKEW, PhD‡

INTRODUCTION

HISTORICAL ROLE OF THE IMPORTANCE OF FOOD IN MILITARY OPERATIONS

ENVIRONMENTAL STRESS AND NUTRIENT REQUIREMENTS

Cold

Altitude

Heat

Stress of Military Training, Oxidative Stress, and Immune Function

Sports Nutrition and Military Nutrition: Similarities and Differences

SUMMARY

*Assistant Professor, Department of Physical Therapy and Exercise Physiology, University of Massachusetts-Lowell, 301 Solomont Way, Suite 5, Lowell, 

Massachusetts 01853

†Chief, Military Nutrition Division, US Army Research Institute of Environmental Medicine, Building 42, Kansas Street, Natick, Massachusetts 

01760-5007

‡Colonel (Ret), Medical Service Corps, US Army; Professor and Director, Division of Nutrition, University of Utah, College of Health, 250 South 1850 

East #214, Salt Lake City, Utah 84112
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Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

INTRODUCTION

resupply is reliable, nutrition may diminish in importance, compared with other aspects of combat readiness. 

Thus, when harsh weather or extreme environmental 

conditions are superimposed on the physical demands 

of military operations, nutrition rapidly becomes a 

prime factor for maintaining performance and preventing disease and injury (Figure 6-1).1

It is widely recognized that food has a significant 

impact on performance. Even in the early part of the 

19th century, Baron Dominique Jean Larrey, Inspector 

General of Napoleon’s Military Medical Staff, wrote 

about the medical conditions and experiences that occurred during Napoleon’s disastrous winter campaign 

against the Russians in 1812: 

The ice and deep snow with which the plains of Russia 

were covered, impeded...calorification in the capillaries and pulmonary organs. The snow and cold water, 

which the soldiers swallowed for the purpose of allaying their hunger or satisfying their thirst...contributed greatly to the destruction of these individuals by 

absorbing the small portion of heat remaining in the 

viscera. The agents produced the death of those particularly who had been deprived of nutriment.1

Dr Larrey’s words provide a dramatic illustration of 

the significance of food to military performance. 

Most military field commanders acknowledge the 

importance of food for morale purposes, as evidenced 

by Anthony Kellett’s account of rations in Combat Motivation: The Behavior of Soldiers in Battle: “...a lack of food 

(is) the single biggest assault on morale” and “...nothing 

weakened the will to fight more than did hunger.”2(p 244)

However, other commanders do not consider food to be 

as important to mission planning as weapons, tactics, 

vehicle fuel, and other logistical needs.3 In temperate 

environments, where food and water are plentiful and 

HISTORICAL ROLE OF THE IMPORTANCE OF FOOD IN MILITARY OPERATIONS

Some military commanders tend to overlook mundane, but important, lessons learned about nutrition 

from past campaigns. LGCE Pugh, MD, a British physician and high-altitude physiologist, once observed 

that, “Military people, with due respect, will never 

listen to physiologists, and, what’s more, they will 

never take lessons from the past. They always have 

to start everything again from the beginning and find 

out the hard way. It’s always been so and always will 

be so.”4(p 355)

Despite Pugh’s pessimistic view, the military has 

spearheaded important advances in our understanding 

of nutritional disease. Dr Kenneth J Carpenter observed 

that the early British and Japanese navies were misled 

by prevailing theories of disease and, as a consequence, 

were ravaged by diet-related scurvy and pellagra during 

polar expeditions at sea and bitter land campaigns in 

Manchuria.5 However, lessons learned have been applied, and the record of the US military since World War 

II in recognizing the role of rations and food technology in military medicine is encouraging.6

 Johnson and 

Kark7 reviewed post–World War II reports on military 

feeding problems that related to the environment. They 

concluded that US soldiers were, in large part, able to 

avoid needless injury in desert, jungle, mountainous, 

and Arctic theaters because of the superiority of their 

rations. WB Bean, MD, a nutrition officer during World 

War II, summarized the role of nutrition in American 

troops both in garrison and in combat8,9:

In the last year of the war (World War II) we went 

to the Pacific where we were able to study garrison 

troops and those in combat ... . They had been in serious combat for 4 months of almost daily fighting. The 

improved C-ration was the only food they had. They 

were the fittest group we tested anywhere.

Considerable discussion of the proper amount and 

optimum nutrient composition of military rations 

continues in today’s modern military.10–16 In retrospect, 

however, many recommendations concerning the 

Fig. 6-1. Malnourishment contributed to the misery of Civil 

War soldiers. Photograph shows a Civil War hospital wing.

Photograph: Reproduced from the National Archives and 

Records Administration, Washington, DC. Matthew Brady, 

photographer.
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Nutrition and Military Performance

nutrient composition of military rations have changed 

little since World War I, as evidenced by a 1919 report 

by Murlin and Miller: 

The amount of protein...sufficient to repair all of the 

wastes of the body and to supply an adequate reserve 

is 13% of the total energy intake. It seems a matter of 

indifference to the muscles whether they receive their 

energy from carbohydrate or from fat ... . Hard muscular work, therefore, can be done on a diet high in carbohydrate or upon a high fat diet. It is of general experience, however, that muscular work is done with less 

effort if there is a plentiful supply of carbohydrate.17

An example of current nutritional practices that are 

similar to those described by Murlin and Miller is the 

observed protein intakes in several military surveys, 

which typically ranged from 13% to 15% (Figure 

6-2).18 Modern military rations have an admirable 

track record of supporting performance in a variety of 

moderate environments6; however, the situation may 

change rapidly in theaters of operation characterized 

by more extreme temperatures and terrain.19,20 Rodahl 

and Issekutz21 state the following:

While short-term nutritional deficiencies in men at 

room temperature appear to have little or no detrimental effect on the capacity to do short term, 

heavy work, there is a marked reduction in physical work capacity when a nutritional deficiency 

or nutritional stress is superimposed upon a cold 

stress.21

Based on literature available from field nutritional 

surveys, the stress from the physical, emotional, and 

psychological events surrounding peacetime training22,23 and combat6,8 is usually adequately held at bay 

by the nutrients provided by conventional military 

field rations. It is not until stressors such as

• extreme heat, 

• cold, 

• altitude, 

• sleep deprivation, or 

• caloric restriction 

Fig. 6-2. World War I soldier eating rations in the field. Major 

John Murlin and his research teams conducted extensive 

studies on energy intake, weight changes, and macronutrient consumption in the Army in an effort to reduce wasting 

of food in the military. 

Photograph: Reproduced from the National Archives and 

Records Administration, Washington, DC. 

are superimposed that performance becomes jeopardized.19,20,24 Furthermore, these effects may vary between 

sexes, warranting different considerations for male 

and female nutrition in extreme environments. Recent 

changes in the roles of female soldiers in combat have 

led to the realization that our knowledge of nutritional 

requirements for female service members and male–

female differences in nutritional requirements may be 

incomplete.25,26 Male soldiers have been the subject of 

numerous investigations of nutritional requirements 

and ration developmental efforts, but little research has 

been directed toward the unique nutritional requirements of female service members.25 Thus, the scope of 

this review will cover only the effects of environmental extremes on a known nutritional challenge facing 

female soldiers: iron availability.27 Future research is 

required to determine other potential gender differences in military service members’ nutritional needs. 

ENVIRONMENTAL STRESS AND NUTRIENT REQUIREMENTS

The complex interrelationship of environment and 

human physiology and performance is depicted in 

Figure 6-3. Energy and fluid deficits arising from the 

interaction of environment and nutrition can potentially result in both physical and mental performance 

decrements.28,29Comprehensive reviews of the interaction of environment and nutrition within a military 

context can be found in workshop publications by the 

Committee on Military Nutrition, Food and Nutrition 

Board, Institute of Medicine, National Academy of 

Sciences.19,20

Cold 

After World War II and the Korean War, the influence of cold stress on vitamin requirements was a 
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Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

focus of considerable military and civilian research.30

A clear picture emerged from this research establishing 

that, although caloric requirements can be elevated, 

vitamin and mineral requirements are not significantly 

increased by cold exposure.31 Work in the cold can be 

adequately supported by a variety of combinations 

of dietary fat, carbohydrate, and protein, although 

there is some evidence that certain combinations of 

macronutrients may be more beneficial than others in 

the ability of soldiers to withstand cold exposure.32,33 

The compounding effects of intense activity and cold 

exposure may require more selective nutrient intake. 

Recent evidence suggests an effective shift from carbohydrate to fat and protein utilization during low-tomoderate intensity shivering in the glycogen-deficient 

states prevalent in extended field operations.34 However, other experiments revealed that more intense 

cold-induced shivering increases muscle glycogen 

utilization, thus increasing the need for dietary intake 

of carbohydrate.35 The effect of macronutrient source 

is not as practically significant compared with the 

consumption of enough total calories to support activity and thermogenesis. The duration and magnitude 

of cold exposure, as well as the energy requirements 

of the activities being performed in the cold, should 

be considered when determining appropriate dietary 

intake during cold exposure. Total energy expenditure in cold environments has been documented to 

increase as much as 20% in military personnel36—an 

effect attributable to the increased physical demand 

associated with heavy equipment and clothing and 

traversing difficult terrain (ie, ice and snow). Cold 

exposure alone may cause increases in metabolic rate, 

and thus energy requirements if shivering is elicited, 

because energy demands increase during shivering 

thermogenesis.37 However, modern cold weather 

protective clothing effectively limits the degree of cold 

stress experienced by exposed personnel, and shivering may not be substantial enough to impact overall 

energy requirements. David Bass,38 an Army thermal 

physiologist from the US Army Research Institute of 

Environmental Medicine, explained that: “Man in the 

cold is not necessarily a cold man!” However, energy 

deficiency (ie, negative energy balance)—induced by 

inadequate intake, in concert with elevated stressors 

such as physical exertion and sleep deprivation—impairs the metabolic (and vasomotor) response to cold 

exposure, thus increasing the risk for hypothermia.39–41

Therefore, increases in total energy intake may be required during prolonged cold weather military operations to offset energy demands of increased work and 

to prevent cold injury, even when clothing is adequate 

enough to reduce shivering (Figure 6-4). The increase 

in total calorie requirements is mainly caused by inInappropriate

Thirst Response

extreme

environments

Heat, Cold, Altitude

Increased

Water Requirements

Decreased

Availability of

Water

Dehydration

Increased

Energy

Requirements

Inappropriate

Appetite Response

Decreased

Availability

of Food

Negative Energy

Balance

Impaired Thermoregulation • Depleted Muscle Glycogen • Deterioration of Fine Motor Coordination

Impaired Effectiveness • Diminished Work Capacity

Fig. 6-3. Extreme environments and their influence on physiological function. This generalized cascade of events demonstrates 

how environment can influence food and water consumption and thus performance. 

Illustration: Adapted with permission from Askew EW. Nutrition and performance in hot, cold, and high altitude environments. In: Wolinski I, ed. Nutrition in Exercise and Sport. Boca Raton, Fla: CRC Press; 1997. 
161

Nutrition and Military Performance

creased physical exertion, because it is unlikely that 

cold exposure itself, in adequately clothed individuals, increases energy requirements more than 10%.32,33

Female soldiers may encounter different challenges in cold environments, compared with their 

male counterparts. Research on iron requirements and 

the thermogenic response to cold has identified iron 

as a key micronutrient sustaining thermoregulation 

of women exposed to a cold environment.39,40 Women 

usually consume fewer total food calories than men 

(proportional to their smaller stature), raising the possibility that female soldiers deployed in cold weather 

could consume less than the recommended dietary 

allowance (18 mg), which could impair thermoregulatory response to cold. Whether female soldiers should 

receive iron-fortified rations is a complex issue that 

will be discussed later in this chapter. 

Although nutrient requirements in the cold are important considerations, they are somewhat secondary 

to nonnutritional aspects of cold weather operations, 

such as proper clothing and training. The role of 

macronutrient mixture becomes more relevant when 

cold exposure is combined with high altitude, an environment that presents its own unique challenges to 

maintain proper nutrition in the soldier.20

Altitude

Nutrition surveys conducted with military service 

members deployed at altitude have shown that early 

onset of altitude illness reduces appetite and, subsequently, energy and carbohydrate intake (Figure 

6-5).42,43 This reduced energy intake, combined with the 

higher energy expenditure observed at altitude (compared with sea level), leads to the tendency for soldiers 

to be in negative energy balance at altitude.36,44,45 Food 

intake usually increases with time and acclimation, but 

never meets the level of intake observed at sea level. 

Weight loss and performance decrements are common 

under these conditions; thus, altering macronutrient 

composition may be important in maintaining proper 

Fig. 6-4. Data collection for the 1986 USARIEM (US Army 

Research Institute of Environmental Medicine) field study 

of MREs (Meals, Ready to Eat), compared with Ration, Cold 

Weather (RCW) in Alaska. Data collectors are reviewing 

dietary records and collecting specimens for doubly labeled 

water energy expenditure measurements from one of the 

soldiers participating in the study.

Fig. 6-5. Data collection techniques for the 1990 USARIEM (US Army Research Institute of Environmental Medicine) field 

study of carbohydrate supplementation at altitude. This study was conducted during a military operation at high altitude in 

Bolivia and demonstrated the value of energy supplementation to offset the anorexic effect that occurs in the first few days 

at altitude. Recipe specialists completed detailed analyses of food preparation in the kitchen (a) and dieticians (Lieutenant 

Colonel John Edwards, Army Catering Corps, United Kingdom, shown here) conducted detailed premeal and postmeal 

estimations of food choice and food waste (b).

a b
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Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

nutrition at altitude. For example, although fat is an 

efficient and well-tolerated energy source during cold 

weather operations at sea level, it is not as well tolerated at altitude.32 Carbohydrate supplementation of 

the military diet during field operations at altitudes 

exceeding 2,200 m is usually an effective method of 

increasing both carbohydrate and total energy intakes,45,46 and may decrease early symptoms of altitude 

sickness,47,48 although not all studies confirm this effect.49 Nevertheless, the substitution of carbohydrate 

for fat and, to a certain degree, for protein can provide metabolic advantages to an individual’s oxygen 

economy while working at altitude (Figure 6-6).50 An 

enhancement of both short-term, high-intensity exercise and long-term, submaximal exercise performance 

by carbohydrate supplementation at altitude has also 

been noted.42,48 Carbohydrate is a more efficient fuel at 

altitude than fat because it is already partially oxidized. 

For example, more oxygen atoms are associated with 

1 mol of glucose (molecular weight: 180) than with 

an entire mole of palmitate (molecular weight: 256). 

The metabolism of carbohydrate for energy requires 

approximately 8% to 10% less inspired oxygen than 

that required to process a similar amount of calories 

from fat.

In practical terms, a high carbohydrate diet may 

reduce the symptoms of acute mountain sickness; 

enhance both short-term, high-intensity work, as well 

as long-term, submaximal efforts; and lower the effective operating elevation as much as 300 to 600 M.29,50

The most effective carbohydrate supplementation is 

usually in the form of liquid beverages; soldiers will 

drink even when they are reluctant to eat.45,49 Increasing 

fluid and carbohydrate intake is beneficial at altitude 

where fluid losses are increased because of diuresis and 

humidifying expired air in a usually dry atmosphere 

(Figure 6-7).51 

Although female soldiers would also benefit from 

carbohydrate supplementation at altitude, iron may be 

a more important dietary component to monitor in this 

Fig. 6-6. Data collection procedures in the 1988 USARIEM (US Army Research Institute of Environmental Medicine) field 

study at the Marine Mountain Warfare Training Center, Pickle Meadows, California. This was a winter study involving high 

intensity work at altitude. Some of the measurements included (a) dietary intakes based on detailed dietary interviews with 

a dietician; (b) maximal aerobic capacity measurement on a stationary bicycle; (c) cardiovascular function tests, including 

EKG (shown here being administered by Captain Van Hubbard, National Institute of Diabetes and Digestive and Kidney 

Diseases [NIDDK]); and (d) biochemical markers were assessed from fasting blood samples drawn from the Marine volunteers.

a b

c d
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Nutrition and Military Performance

population. Studies of women at altitude reveal similar 

findings to studies of women in the cold in that there is 

an increased need for dietary iron to mediate adaptive 

responses to the new environment. Research conducted 

in the late 1960s identified that female service members 

deployed to moderate-to-high-altitude environments 

would require supplemental dietary iron to optimally 

support their hematopoietic response to hypoxia.52This 

presents further evidence of the need to closely monitor iron intake in female soldiers deployed to extreme 

environments (ie, cold or altitude).53–54

Heat

Not surprising, the most important nutritional 

considerations for military operations in the heat are 

fluid and electrolyte replacement, which are discussed 

in detail in other chapters in this volume. There are, 

however, a few studies suggesting that macronutrient 

composition may play a role in optimal performance 

in the heat. Some55 but not all56 authors recommend 

increasing carbohydrate consumption to compensate 

for increased utilization of muscle glycogen stores and 

glucose during hyperthermic exercise. The inclusion of 

carbohydrates in rehydrating fluids can serve a practical purpose by increasing palatability and promoting 

fluid intake,56 irrespective of whether metabolic fuel 

use is altered in the heat. Total energy expenditure of 

military personnel does not seem to differ between hot 

and temperate environments.36 Thus, from a practical 

standpoint, the total amount of calories consumed in 

the diet does not need to be adjusted in hot climates.

Stress of Military Training, Oxidative Stress, and 

Immune Function

As our understanding of the relationship between 

oxidative stress and chronic disease becomes clearer, a 

stronger impetus for reinvestigating the optimum level 

of antioxidant vitamins and minerals in the military diet 

may emerge. Immune function can be compromised 

in states of high oxidative stress, such as prolonged 

physical activity combined with caloric restriction and 

sleep deprivation.57 Studies of US Army Ranger candidates engaged in 8 weeks of training involving high 

levels of physical exertion, sleep deprivation, mental 

stress, and food restriction revealed impaired immune 

response in these soldiers.58–60 Work at altitude may be 

a particular challenge to human antioxidant defense 

systems caused, in part, by hypoxia, diet, ultraviolet 

light, and exhaustive physical activity.61–64 Other data 

have demonstrated elevated markers of oxidative stress 

and impaired immune function, such as breath pentane, 

during certain types of military training (Figure 6-8).63

Thus, a natural question remains as to whether administering antioxidant supplements might mitigate these 

responses. A 2006 review article by Gleeson65—reporting 

Fig. 6-7. Hydration status has been a key variable in USARIEM (US Army Research Institute of Environmental 

Medicine) field nutrition studies. Lieutenant Colonel E 

Wayne Askew organizes 24-hour urine collections with Major 

Nancy King (a) and records specific gravity measurements 

made by Elaine Christensen (b) in field laboratories at Fort 

Riley and at altitude in Bolivia.

a b
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Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

Fig. 6-8. Breath pentane sampled at several time periods 

during field training at moderate altitude. Breath pentane 

sampled at the start (Day 0), in the middle (Day 6), and at 

the end (Day 14) of 14 days of US Marine cold weather field 

training (elevation 7,000–9,000 feet). The Marines ate military 

field rations during the training period. The antioxidant 

supplement consisted of vitamins A, E, and C plus selenium 

and zinc. Pentane is a hydrocarbon given off following the 

peroxidation of omega-6 fatty acids in response to free radical 

damage (oxidative stress). 

Illustration: Adapted with permission from Chao W-H, 

Askew EW, Roberts DE, Wood SM, Perkins JB. Oxidative 

stress in humans during work at moderate altitude. J Nutr. 

1999;129:2009–2012.

Placebo

Antioxidant

Pentane, nmoL/L

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

Day 0 Day 6 Day 14

the effects of antioxidant supplementation on immune 

function—found that, whereas it is likely that vitamin 

and mineral supplements would improve immune 

function in individuals exhibiting a deficiency of these 

factors, it remains to be determined whether administration of an antioxidant supplement would help reduce 

associated oxidative stress and subsequently bolster 

the immune response in otherwise healthy individuals.Endurance exercise alone is thought to upregulate 

inherent antioxidant production, although prolonged 

endurance activity may result in higher concentrations 

of reactive oxygen species than can be handled by this 

training response. Therefore, low-level supplementation 

of antioxidant vitamins (eg, A, E, C, and beta-carotene) 

may be warranted in individuals participating in prolonged intense training. 

In addition to considering the total energy intake, 

dietary macronutrient composition could also affect 

immune function.59,60 For example, even moderate 

dietary protein deficiency has been shown to impair 

immune function,65 and carbohydrate supplementation 

during prolonged strenuous exercise attenuates markers of elevated immune response. However, it does not 

appear that carbohydrate supplementation alleviates 

the effects of intermittent strenuous activity on immune function, as seen in military field operations.65

Finally, whereas consideration of antioxidant supplementation in extreme immunodepressive conditions 

may warrant further consideration, the dangers of 

oversupplementing with antioxidant nutrients (at high 

levels that could potentially impair immune function) 

must also be carefully considered. As an example, iron 

deficiency is associated with impaired immune function, 

and, as described previously, female soldiers may be at 

greater risk for iron deficiency.26 Although increasing the 

iron content in military rations is one possible solution 

to this problem, the interaction of excess dietary iron 

and reactive oxygen species produced during exercise 

and certain types of environmental exposure suggests 

that caution may be warranted.66 For instance, if 18 mg 

of dietary iron intake was contained in a typical female 

caloric intake of 2,000 kcal/d, then a male or female service member ingesting 4,000 kcal/d would receive twice 

as much or approximately 36 mg of iron/d. Ferrous iron 

is a cofactor in the propagation of certain harmful free 

radicals, and excess dietary iron may be undesirable 

under conditions of increased oxidative stress.67,68

Sports Nutrition and Military Nutrition: 

Similarities and Differences

Military performance shares much in common with 

athletic performance.69,70 Optimal nutrition to sustain and 

enhance physical and mental performance for athletic 

competition will also have application to military training and combat operations. However, there are some 

significant differences. During military operations, it is 

impossible to predict exactly when an intense work period will begin and how long it will have to be sustained. 

This inherent uncertainty tends to make a classical sports 

nutrition approach to military feeding and diet planning 

less useful. The enhancement (or at least the sustainment) 

of performance of military tasks is best accomplished 

by providing a basic ration or feeding system that 

• maintains body weight, 

• provides adequate nutrients for the prevention of nutrient deficiencies, 

• provides adequate protein, and 

• maximizes carbohydrate intake.10,11,40

Careful attention to these factors ensures that soldiers enter combat with high levels of muscle glycogen (a significant factor in short-term, high-intensity 
165

Nutrition and Military Performance

performance) and protects them from vitamin and 

mineral shortages that might arise from sporadic ration 

consumption during combat. Exhibit 6-1 lists a variety 

of military rations reflecting specific purposes of each 

ration, and also the improvements in ration development over time.

Role of Vitamins in Physical Performance 

Friedl and Hoyt70 and van der Beek and colleagues71–74 have studied the impact of varying severities of vitamin restriction on physical performance. 

Dietary vitamin deficiencies produced progressive 

physical performance impairments. At 60% of recommended daily allowance, restricted intakes of thiamin, 

riboflavin, pyridoxal phosphate, and ascorbate did 

not result in a significant performance decrement 

(maximum workload) after 10 weeks at this level of 

restriction (Figure 6-9). This can be contrasted with 

the more immediate effect of acute75,76 and long-term 

chronic77 dietary carbohydrate restriction on physical 

performance (Figures 6-10 and 6-11). Physical performance is much more sensitive to the amount of 

carbohydrate in the diet in the short term (days) than 

it is to the vitamin, protein, or fat content.69 

Role of Carbohydrates in Aerobic Endurance 

Performance

Both the length of time provided for dietary adaptation to carbohydrate restriction and the amount 

of carbohydrate in the diet can influence the level of 

aerobic endurance performance. Figure 6-4 illustrates 

that aerobic endurance performance can be reduced by 

40% after only 4 days on a calorie-adequate, but low 

carbohydrate diet75 (10% kcal). For 2 weeks, a similar 

calorie-adequate, low carbohydrate diet (5% kcal) 

also reduced performance, but only by approximately 

15%, presumably because of tissue-level adaptations 

to the shift in energy sources76 (Figure 6-11). Furthermore, a reduction in dietary carbohydrate from 83% 

kcal to 57% kcal had only a small (5%) reduction in 

performance under similar exercise conditions.76 The 

short-term effects of carbohydrate deprivation may 

be more relevant to military operations, in which case 

the observed adaptive response in the 14-day study 

may not apply, and soldiers may find that endurance 

performance is decreased when carbohydrate intake 

is reduced. The effect of any reduction in dietary carbohydrate intake depends on both the period of time 

over which it is reduced and its absolute level in the 

diet. Although the studies previously described were 

not conducted on soldiers, other studies using military 

test subjects and work performance tests of similar 

intensity to military tasks or actual military field 

maneuvers77 have shown that reduced carbohydrate 

intake has the potential to negatively influence muscle 

glycogen levels and endurance.78

There is abundant evidence in the sports medicine 

literature to permit extrapolation to military physical performance and to conclude that certain types 

of military performance may also be impaired by an 

acute shortage of carbohydrate in the diet. Inadequate 

carbohydrate in the diet—coupled with successive days of intense, prolonged exercise (sustained 

operations)—may result in a gradual reduction of 

glycogen stores, deterioration of performance, and 

perception of fatigue/work intensity.79 The effect of 

muscle glycogen depletion on perception of exertion 

is shown in Figure 6-12. As a result of dietary carbohydrate deficiencies, certain military tasks, such as 

load-bearing work, may be perceived by soldiers to 

be more difficult.80 Carbohydrates may be effective in 

extending or enhancing military performance when 

taken before, during, and after moderate- to highintensity aerobic exercise.81 Thus, they may be helpful 

to soldiers as a preload before going into the field, as 

well as during field training, to sustain performance; 

carbohydrates may also be helpful to soldiers during 

postfield operations to speed recovery of local muscle 

and overall fatigue. This would require a consumption of approximately 500 to 550 g of carbohydrate 

daily (for male soldiers).82A review of 18 field studies 

of typical dietary carbohydrate intakes of male soldiers in temperate, hot, and cold environments fed a 

variety of rations revealed intakes ranging from 244 

to 467 g per day.83 Both the mean and median intakes 

in these 18 studies were 350 g of carbohydrate per 

day (Figure 6-13). It is apparent that a typical daily 

350 g carbohydrate intake, under the best conditions 

(training, not combat), is considerably less than the 

500 to 550 g range recommended for optimal glycogen 

repletion and physical performance.81,82 Total caloric 

intake by soldiers during military field operations 

is often less than that required to maintain energy 

balance (Exhibit 6-2).83 Soldiers do not selectively 

consume low carbohydrate diets during field training operations; however, total carbohydrate intake 

is often low simply because total energy intake is 

low. Often, the rations are “field-stripped,” meaning 

that soldiers select from the complete ration whatever items can be eaten on the move—regardless of 

nutrient content—thus leaving the remaining food. 

Stripping rations may also make the food less bulky 

to carry and may reflect individual biases regarding 

food nutritional value, quality, or taste. Inadequate 

food consumption in the field has been ascribed to 

the following:
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Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

EXHIBIT 6-1

A BRIEF HISTORY OF RATIONS

Fig. E1-1. Field Ration, individual—the K Ration of World 

War II.

Photograph: Reproduced from the National Archives and 

Records Administration, Washington, DC.

(Exhibit 6-1 continues)

Historically, ration development was dependent on what 

was available and what could be transported without 

spoiling. Under such constraints, the rations were 

designed around stable foods that could be stored for 

long periods without spoiling and that could physically 

withstand the elements of war and field training (Exhibit 

Figure E1-1). Although some effort was made to provide 

fresh food to soldiers during those years, the logistics of 

providing large quantities of fresh meat or vegetables in 

a war zone were challenging, and such efforts were rarely 

successful. Thus, in addition to adverse climatic and 

battlefield conditions, many soldiers were malnourished 

and suffered illness as a result.

Improvements in food preparation and packaging technology, as well as increased availability of prepackaged 

foods, changed the focus of ration development. Current 

ration research considers the macronutrient and micronutrient composition of the foods for each ration under 

varying conditions. Supplements, or completely separate 

rations, are available for cold weather operations, altitude, 

and extended field exercises requiring a high level of 

sustained physical intensity. Even though the operational 

environments differ significantly, the requests for ration characteristics are the same: small, lightweight, high calories, 

and most of all acceptable—if not appealing—to the soldier who has to consume the ration. This has been a focus of 

the Department of Defense Combat Feeding Directorate at the US Army Natick Soldier Research, Development, & 

Engineering Center. The taste, texture, and appearance of a ration needed to be taken into consideration as much as 

the nutrient content. Dr Ancel Keys made the observation that, “A ration that will not be eaten is worse than useless.”(1) 

Ironically, the K ration, named after Keys, is now a classic example of nutritionally balanced to the point of impalatability. 

Ration Description Function

Civil War—Marching Ration Salt pork or fresh meat, hard bread Field Ration (individual)

(“hardtack”), sugar, coffee, salt

Civil War—Camp Ration Pork/bacon, soft bread, beans, coffee or tea, Garrison Ration (Group Ration)

sugar, salt, pepper, potatoes, vegetables, 

dried fruits, soap

World War I—Reserve Ration Similar to Civil War Marching Ration: Reserve Ration = individual

and Trench Ration canned meat instead of salt pork Trench Ration = Group Ration (25

soldiers)

World War II: A Ration Fresh/frozen meat, fresh dairy, fresh fruits Field Kitchen Ration

and vegetables, perishables require 

preparation

World War II: B Ration Canned, dried, dehydrated, nonperishables Field Kitchen Ration (up to 100 soldiers,

require preparation could also be broken up into 10-in-1 

ration for small group feeding)

World War II: C Ration Bread or crackers, spread, meat or protein- Combat Ration (individual)

based entree, dessert packaged in cans, 

coffee, sugar, gum, cigarettes and matches

World War II: D Ration Chocolate bars, highest caloric value ration, Survival Ration

3 × 4 ounce bars—highly palatable, useful 

in all climates, no preparation required
167

Nutrition and Military Performance

World War II: K Ration Highest nutritional value, lightweight, low Field Ration: individual

palatability

Vietnam: Long-Range Patrol Freeze-dried entrees—require water for Field Ration: Special Forces restricted 

rehydration; lightweight, high caloric value use—not nutritionally adequate for

extended time periods

MRE Complete meal, freeze-dehydrated Field Ration: individual; replaced C 

 Ration

T Ration MRE in steam-table tray Group feeding ration (18 soldiers)

Specialty MREs:

Mountain Lightweight, food could be prepared at Field Ration: altitude

higher altitude (or come precooked), high 

calories, more “roughage” to assuage hunger

Arctic Supplement Additional 900-calorie packet to be used in Field Ration: cold weather

combination with MRE; contains 

“warming foods,” such as soups, hot 

beverages, snacks, and styrofoam 

containers and cups

Cold Weather Meal High-calorie, extra drink mixes to promote Field Ration: extreme cold weather

water consumption, packaged in white 

camouflage

Carbohydrate Supplement Eat-on-the-move snacks to supplement Field Ration: prolonged, intense

(CarboPack) MREs, 380 calories, 75 g carbohydrates physical activity

MRE: meal, ready-to-eat

Note: Many other specialty rations and supplements have now been created, for example, Humanitarian Daily Ration, Kosher 

Hotel Ration, Survival Food Packets, and the First Strike Ration.(2)

Data sources: (1) Keys A. Quartermaster Review. 1941;XXI(2, Sept/Oct):26–27. (2) Department of Defense. Operational Rations of the 

Department of Defense. 8th ed. Natick, Mass: US Army Natick Soldier RD&E Center/DoD Combat Feeding Directorate; May 2010. 

Natick PAM 30-25. OPSEC 08-481.

Exhibit 6-1 continued

• poor ration palatability, 

• menu boredom, 

• inadequate time to eat or prepare meals, 

• anxiety, and 

• intentional dieting to lose weight.11

Whatever the cause, this “voluntary anorexia” of 

soldiers in the field results in reduced total energy 

and carbohydrate intake. The lack of energy (calories) 

itself is not as significant a concern in the short run as 

is the lack of carbohydrate.84 The levels of carbohydrate 

consumed by soldiers is frequently within the range 

of carbohydrate intake observed in controlled laboratory studies, resulting in reduced muscle glycogen 

concentrations and reduced levels of submaximal 

aerobic performance.79,81,82

The impact of dietary carbohydrate content on 

military performance is difficult to study under 

operational conditions because of manifold uncontrolled variables encountered in combat conditions, 

real or simulated. Thus, definitive field studies demonstrating a positive effect of dietary carbohydrate 

supplements on military performance are lacking.85 

However, when field conditions can be simulated 

under well-controlled laboratory settings, results suggest that performance is improved after carbohydrate 

supplementation. For example, 18 physically fit US 

Army Special Operation Forces soldiers completed 

a study designed to test the concept that soldiers 

would benefit from carbohydrate supplementation 

during field operations (Figure 6-14).86 These military 

test subjects were fed a controlled diet that simulated typical carbohydrate and protein intakes (327 

g carbohydrate/d, 201 g fat/d, and 118 g protein/d, 

supplying a total of 3,657 kcal/d) during field operations. The soldiers exercised daily (11 days total) 

under conditions designed to simulate field energy 

expenditure patterns (intermittent, as well as sustained activity patterns of varying intensity levels). 

In addition to the standard diet, each test subject 

received one of three beverage supplements during 

the field-simulated diet and exercise program: 
168

Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

Fig. 6-10. Effect of short-term carbohydrate intakes on the 

performance of intermittent work. Diets were consumed for 

4 days before cycle ergometer work at 70% maximal aerobic 

capacity. The high carbohydrate diet contained 77% of its 

calories from carbohydrate, whereas the low carbohydrate 

diet contained only 10% of its calories from carbohydrate. 

Illustration: Adapted with permission from data reported in

Galbo H, Holst JJ, Christensen NT. The effect of different diets 

and insulin on hormonal response to prolonged exercise. 

Acta Physiol Scand. 1979;107:19–32. Endurance Test, min 120

100

80

60

40

20

0

High Low

Fig. 6-9. Effect of a restricted vitamin intake (60% RDA) on 

functional performance in humans. This illustration shows 

10 weeks’ consumption of either 100% or 40% of the recommended daily allowance for thiamine, riboflavin, pyridoxal, 

and ascorbate on functional performance (cycle ergometer 

work) in humans. Note that, even after 10 weeks at 60% 

vitamin restriction, performance was only decreased approximately 17%. 

RDA: Recommended Dietary Allowance

Illustration: Adapted with permission from van der Beek EJ. 

Marginal Deficiencies of Thiamin, Riboflavin, Vitamin B-6 and 

Vitamin C: Prevalence and Functional Consequences in Man. 

Amsterdam, The Netherlands: TNO Toxicology and Nutrition Institute; 1992. Maximal Workload, Watts

350

300

250

200

150

100

50

0

Control

100%

RDA

Deficient

40%

RDA

Week 2

Week 6

Week 10

Fig. 6-11. Effect of several levels of long-term (14 days) carbohydrate intake on the performance of intermittent cycle ergometer work. Diets contained high (83%), moderate (56%), 

or low (24%) amounts of their energy from carbohydrate. 

Illustration: Adapted with permission from data reported 

in Pruett EDR. Glucose and insulin during prolonged 

work stress in men living on different diets. J Appl Physiol. 

1970;28:199–208. Endurance Test, min 180

160

140

120

100

80

60

40

20

0

High Moderate Low

Fig. 6-12. Muscle glycogen depletion and perceived exertion 

during strenuous training. Note that exhaustion approaches 

as glycogen levels decrease. 

Illustration: Adapted with permission from Sherman WM, 

Costill DL. The marathon: dietary manipulation to optimize 

performance. Am J Sports Med. 1984;12:44–51. % Exertion Muscle Glycogen Exhaustion

Heavy

Moderate

Light

High

Moderate

Low

0 0.5 1.0 1.5
169

Nutrition and Military Performance

1. placebo, 

2. carbohydrate (180 g) once a day immediately 

after exercise, or 

3. carbohydrate (180 g) divided into several 

doses taken after the morning exercise session 

and at intervals during the afternoon exercise 

session. 

The drop in respiratory exchange ratio that occurred over the 11-day study is illustrated in Figure 

6-15. This drop in respiratory exchange ratio was expected and indicated that the soldiers were experiencing a carbohydrate shortage in response to the dietexercise field simulation and also were experiencing 

a switch to a fat-predominant metabolism. The provision of supplemental carbohydrate permitted a higher 

level of physical performance or aerobic power to be 

obtained. Run times to exhaustion were increased 

approximately 6%, with the single carbohydrate feeding and 17% with the divided dose (Figure 6-16). The 

ingestion pattern of the carbohydrate supplement 

appeared to influence performance, indicating that 

a supply of easily consumed carbohydrate supplement or food item ingested before, during, and after 

military field activities would be an effective method 

to sustain or boost soldier physical performance. A 

recent review by Montain and Young40 suggests that 

liquid carbohydrate consumption may be a practical solution to the reduced food intake in the field, 

because it can be consumed during activity.

How Critical Is Energy Provision?

The previous discussion concerning energy and 

carbohydrate intakes does not necessarily mean that 

soldier performance across a broad spectrum of military tasks will be severely degraded by suboptimal 

energy and carbohydrate intakes. Intense training 

and associated large energy deficits (3,580–4,540 

kcal/d) over 54 hours did not affect energy expenditure or physical activity levels in male and female 

Marines.87A review of the effect of energy restriction 

on military work performance has indicated that 

soldiers can maintain relatively normal work capacities for short periods of food restriction (<10 days).84

The Minnesota starvation studies conducted during World War II demonstrated that energy deficits 

resulting in less than 10% of body weight loss did 

not impair physical performance; however, underconsumption of calories for longer periods of time 

producing continued body weight loss did produce 

significant deficits in physical performance.88 More 

recent studies of food restriction in military scenarios 

have revealed that restricted energy and dietary 

carbohydrate content over a 30-day time period 

supported a light-to-moderate activity level without 

evidence of greatly impaired physical performance 

capabilities.89 Longer periods of caloric restriction 

(8 weeks), however, coupled with higher levels of 

energy expenditure (US Army Ranger training), have 

been associated with significantly reduced physical 

performance capacity.62 Friedl84 has reviewed the 

influence of reduction in body weight caused by 

reduced food intake on muscle strength and aerobic 

capacity. It is difficult to derive a closely predictable 

relationship between energy deficit and performance 

because of the differing experimental conditions 

and performance measures used in various research 

studies. Grip strength, as a performance measure, 

seems to be well preserved in military test subjects 

until nutritional status is severely compromised, 

whereas other measures—eg, maximal lift, maximal 

jump height, isometric leg extension, and maximal 

oxygen uptake—seem to be more sensitive predictors 

of impaired performance.84 Using change in body 

weight as an indirect indicator of energy deficit, and 

estimators of muscle strength and maximal aerobic 

capacity as the dependent variables, generalized relationships between energy deficit and performance 

Fig. 6-13. Typical carbohydrate intakes during military field 

training exercises. Note that more than half the time, dietary 

intake was less than 400 g of carbohydrate per day. This is 

not an adequate amount of carbohydrate to replace glycogen 

used daily in vigorous work (eg, military training). 

Illustration: Reproduced with permission from Baker-Fulco 

CJ. Overview of dietary intakes during military exercises. 

In: Marriott BM, ed. Not Eating Enough—Overcoming Underconsumption of Military Operational Rations. Washington, DC: 

National Academy Press; 1995: 253–283. Frequency 6

5

4

3

2

1

0

Mean Daily Carbohydrate Intakes, g/day

0 250 300 350 400 450 500
170

Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

EXHIBIT 6-2

SEX DIFFERENCES IN ENERGY REQUIREMENTS 

Energy requirements in military operational and training environments vary enormously. One of the most important 

variables in estimating these requirements is body mass, because of the amount of metabolically active tissue, as 

well as the mass that has to be moved through space in any human activity. Body size largely explains the sex differences in energy requirements, although sex steroid hormones also affect energy metabolism at the macronutrient 

level. 

This has been elucidated by a large series of studies using the doubly labeled stable isotope water technique by Reed 

Hoyt and his colleagues at the US Army Research Institute of Environmental Medicine (USARIEM), in close collaboration 

with James DeLany and the energy metabolism laboratory at the Pennington Biomedical Research Center.(1,2) The use 

of this technique to study energy metabolism in natural conditions outside of a metabolism chamber was promoted in 

military studies by Colonel E Wayne Askew, with assistance from Rear Admiral Van Hubbard at the National Institute 

of Diabetes and Digestive and Kidney Diseases (NIDDK). 

Energy requirements are similar for men and women when this is calculated on the basis of body mass. This is highlighted in studies with men and women engaged in the same activity, whether relatively low demand in routine duties or in extraordinarily high demand activities in stressful high-risk training and firefighting (Exhibit Table E2-1). 

Studies of 1 week of Norwegian Ranger training with no organized sleep (<1 hour/day) and no food demonstrated 

that women are more efficient in fat metabolism in a semistarvation setting, an apparent estrogen-related effect.(3,4)

Because of the greater availability of fat stores in most women, compared with normal men, they would also survive 

longer with limited energy intake.

Health and performance are not impaired if energy intake is sufficient to meet the demands.(5) This was demonstrated 

for women exercising intensively and debunked the myth that female soldiers would develop amenorrhea and consequent risks for bone loss and other estrogen-related functions simply from high levels of exercise.(6)

The importance of adequate energy intake was also demonstrated for sustained performance in men, debunking a 

second myth that humans break down with prolonged continuous exercise. Two Norwegian SEALS were studied during a south-north endurance trek of 3,000 km across Greenland and demonstrated that, with an energy-supplemented 

diet of nearly 6,000 kcal/day, body energy stores and performance were sustained, unlike Ranger training with high 

activity and inadequate energy intake.(7,8)

Data sources: (1) DeLany JP, Schoeller DA, Hoyt RW, Askew EW, Sharp MA. Field use of D2 18O to measure expenditure of soldiers 

at different energy intakes. J Appl Physiol. 1989;67:1922–1929. (2) Delany JP. Determination of Total Daily Energy Requirements and Activity 

Patterns of Service Women. Baton Rouge, La: Louisiana State University and A&M College; October 2001, 39 pp. Final Report DAMD17-

96-2-6025. (3) Young VR. Metabolic Response to Food Restriction in Military-Eligible Women Within a Gender Comparison. Cambridge, Mass: 

Massachusetts Institute of Technology; October 1999, 79 pp. Final Report DAMD17-95-2-5014. (4) Hoyt RW, Friedl KE. Field studies 

of exercise and food deprivation. Curr Opin Clin Nutr Metab Care. 2006;9:685–690. (5) Friedl KE. Biomedical research on health and 

performance of military women: accomplishments of the 1994 Defense Women’s Health Research Program (DWHRP). J Women’s 

Health. 2005;14:764–802. (6) Loucks AB, Thuma JR. Luteinizing hormone pulsatility is disrupted at a threshold of energy availability 

in regularly menstruating women. J Clin Endocrinol Metab. 2003;88:297–311. (7) Frykman PN, Harman EA, Opstad PK, et al. Effects 

of a three-month endurance event on physical performance and body composition: the G2 Trans-Greenland Expedition. Wilderness 

Environ Med. 2003;14:240–248. (8) Friedl KE, Moore RJ, Hoyt RW, et al. Endocrine markers of semistarvation in healthy lean men in 

a multistressor environment. J Appl Physiol. 2000;88:1820–1830. 

(Exhibit 6-2 continues)

can be characterized as being similar to those shown 

in Figures 6-17 and 6-18. In general, strength seems 

to be rather well maintained up to 5% of body weight 

loss, and aerobic capacity is only reduced when body 

weight loss exceeds 10%. The interpretation of studies 

appearing to produce data such as those in Figures 

6-17 and 6-18 must be qualified. Maximal aerobic 

capacityis not a good determinant of overall military 

performance. Grip strength, although a useful indicator for severely catabolic or starved individuals, 

does not seem to be a sensitive indicator of energy 

deficit in otherwise healthy soldiers. In addition, the 

relationship between body weight loss and aerobic 

capacity must be expressed independent of body 

weight. It should be noted also that motivation can 

overcome modest physiological decrements, such 
171

Nutrition and Military Performance

TABLE E2-1

SUMMARY OF ENERGY EXPENDITURE STUDIES USING DOUBLY LABELED WATER MEASUREMENTS AND INVOLVING MEN AND WOMEN IN MILITARILY RELEVANT ENVIRONMENTS(1)

TDEE (SD) TDEE/Kg Body Mass

(MJ/d) (MJ/kg/d)

Activity Women Men Women Men

Norwegian Ranger cadet training(2) 21.9 (2.0) 26.6 (2.0) 0.34 0.35

n = 6 n = 10

US Marine recruit crucible exercise(3) 19.8 (0.6) 25.7 (0.8) 0.34 0.35

n = 20 n = 29

Smoke jumpers(4,5) 14.8 (3.0) 20.3 (3.0) 0.23 0.28

n = 9 n = 7

US Marine recruit training(6,7) 9.9 (1.6) 16.9 (4.0) 0.17 0.23*

n = 20 n = 10

US Army mass casualty training(6,7) 12.1 (1.0) 16.4 (3.7) 0.20 0.19

n = 10 n = 6

US Navy sailors at sea(6,7) 11.6 (1.8) 14.4 (3.6) 0.17 0.18

n = 16 n = 9

d: day; MJ: millijoule; SD: standard deviation; TDEE: total daily energy expenditure.

*This study demonstrated significant gender differences when corrected for body weight.

Notes: All TDEE means were significantly different between men and women (P < 0.05). US Marine recruit training was similar for 

men and women, but not conducted in mixed gender teams. 

Data sources: (1) Friedl KE, Ness JW. Upper Limits of Energy Expenditure for Men and Women in Military Operational Settings: Does Female 

Fat Metabolism Provide a Performance Advantage? NATO HFM-158 Symposium on “Impacts of Gender Differences on Conducting 

Operational Activities.” Neuilly-sur-Seine Cedex, France: Research and Technological Organization, North Atlantic Treaty Organization; 2008. (2) Hoyt RW, Opstad PK, Haugen AH, et al. Negative energy balance in male and female rangers: effects of 7 days of 

sustained exercise and food deprivation. Am J Clin Nutr. 2006;83:1068–1075. (3) Castellani JW, DeLany JP, O’Brien C, et al. Energy 

expenditure in men and women during 54 h of exercise and caloric deprivation. Med Sci Sports Exerc. 2006;38:894–900. (4) Ruby BC. 

Training and Extended Operations in Females: Effects on Reproductive Hormones, Bone Health, Task Specific Performance, and Comparative 

Energy Utilization. Missoula, Mt: The University of Montana; October 1999, 60 pp. Final Report DAMD17-96-1-6329. (5) Ruby BC, 

Shriver TC, Zderic TW, et al. Total energy expenditure during arduous wildfire suppression. Med Sci Sports Exerc. 2002;34:1048–1054. 

(6) Delany JP. Determination of Total Daily Energy Requirements and Activity Patterns of Service Women. Baton Rouge, La: Louisiana State 

University and A&M College; October 2001, 39 pp. Final Report DAMD17-96-2-6025. (7) Tharion WJ, Lieberman HR, Montain SJ, et 

al. Energy requirements of military personnel. Appetite. 2005;44:47–65.

Exhibit 6-2 continued

as reduced maximal aerobic capacity. Changes in 

maximal oxygen consumption, in response to modest 

caloric restriction, can influence soldier performance 

to a lesser degree than reductions in muscle strength 

in response to weight loss. The primary concern of 

weight loss from inadequate energy intake during 

military operations appears to be the loss of muscle 

mass and therefore muscle strength. Significant loss 

of muscle strength occurs between 5% and 10% of 

body weight loss (Figure 6-19). Significant declines 

in aerobic capacity can also occur following weight 

losses of this magnitude, but the decline in aerobic 

capacity appears to have relatively little effect on 

soldier performance at moderate levels of sustainable workload.84

There are, however, factors other than strength and 

aerobic capacity to consider when evaluating the effects 

of energy restriction on soldier performance.11 Weight 

losses of 6% or less over periods of 10 to 45 days generally do not produce significant degradations in cognitive 

performance. However, habitual or forced reduction in 

consumption, resulting in greater than 50% loss of energy requirements, may significantly degrade cognitive 

performance.90 Reduced food intake, when coupled with 

other stressors (eg, high rates of energy expenditure 

and sleep deprivation), can impair immune function.64
172

Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

Fig. 6-16. Effect of carbohydrates on performance. This 

illustration shows the effect of carbohydrate supplementation on treadmill performance by the US Special Forces 

soldiers following 11 days of training. The test occurred in 

the afternoon following a 2-hour bout of treadmill running 

in the morning. Carbohydrate was supplemented either as a 

placebo (0 carbohydrate), as a bolus at the end of the preceding bout of exercise, or as a divided dose during and after 

exercise (approximately 180 g carbohydrate supplemented). 

CHO: carbohydrate

Illustration: Reproduced with permission from Murphy 

TC, Hoyt RW, Jones TE, et al. Performance Enhancing Ration 

Components Program: Supplemental Carbohydrate Test. Natick, 

Mass: US Army Research Institute of Environmental Medicine; 1994. Technical Report T95-2. 

Field Diet

CHO Bolus

CHO During and 

After Exercise

Run Time to Exhaustion (min)

100

135

130

125

120

115

110

105

Placebo Divided CHO

Supplement

Bolus CHO

Supplement

Fig. 6-15. Effect of military field diet on respiratory exchange 

ratio. This illustration shows the respiratory exchange ratio 

during exercise over 11 days of suboptimal carbohydrate intakes (300 g/d). Test subjects were US Special Forces soldiers 

performing daily bouts of treadmill exercise.

Illustration: Reproduced with permission from Murphy 

TC, Hoyt RW, Jones TE, et al. Performance Enhancing Ration 

Components Program: Supplemental Carbohydrate Test. Natick, 

Mass: US Army Research Institute of Environmental Medicine; 1994. Technical Report T95-2. Respiratory Exchange Ratio

1

0.9

0.8

0.7

Days of Simulated Field Training

0 2 3 4 5 6 7 8 9 10 11

Fig. 6-14. Sophisticated laboratory metabolic studies have been conducted with the Army at the Pennington Biomedical 

Research Center in Baton Rouge, Louisiana. In a 1993 study of interindividual differences in exercise metabolism, a group 

of Special Force soldiers were housed and tested at the Pennington Center with detailed measurements of metabolic performance during (a) exercise to exhaustion and (b) postexercise. This study revealed more about the value of carbohydrate 

supplementation during exercise than any major differences in fuel metabolism between individuals.

a b
173

Nutrition and Military Performance

Fig. 6-17. Generalized relationship between body weight loss 

and maintenance of strength, based on analyses of several 

military field studies. Strength is well-maintained until body 

weight loss exceeds 10%. 

Illustration: Adapted with permission from Friedl KE. When 

does energy deficit affect soldier physical performance? In: 

Marriott BM, ed. Not Eating Enough—Overcoming Underconsumption of Military Operational Rations. Washington, DC: 

National Academy Press; 1995: 267. % Base Strength 100

80

60

40

20

0

258 11 13 16

% Body Weight Loss

Maintenance of Strength

Reduction of Strength

Fig. 6-18. Generalized relationship between body weight loss 

and maximal aerobic capacity. Note that aerobic capacity 

begins to drop sharply after 10% weight loss is exceeded. 

Illustration: Adapted with permission from Friedl KE. When 

does energy deficit affect soldier physical performance? In: 

Marriott BM, ed. Not Eating Enough—Overcoming Underconsumption of Military Operational Rations. Washington, DC: 

National Academy Press; 1995: 271. % Baseline Maximal Aerobic Capacity100

80

60

40

% Body Weight Loss

Range of Decrements Observed

0 5 10 15 20 25 30

Fig. 6-19. Strength measurements in USARIEM (US Army 

Research Institute of Environmental Medicine) field studies 

of Ranger training included (a) specific grip strength performance (testing shown at the beginning of Ranger training) 

and (b) lifting performance measured in the incremental 

dynamic lift test (testing shown part way through training). 

Grip strength performance was well preserved even in the 

face of large catabolic changes, whereas strength involving 

larger muscle groups, such as the lift test, demonstrated 20% 

reduction, reducing mean strength performance of Ranger 

students to that of the average soldier.

Photographs: Courtesy of Colonel Karl E. Friedl. 

a b
174

Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine

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