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15
Impact of Underconsumption on Cognitive Performance

Mary Z. Mays1

Not Eating Enough, 1995

Pp. 285–302. Washington, D.C.

National Academy Press

BACKGROUND

Conditions on the modern battlefield require that all soldiers be able to perform at their peak. Moreover, higher than normal levels of physical or intellectual performance may be required for long periods of time. Subtle deficits in intellectual behavior can dramatically degrade combat effectiveness, which requires sustained vigilance, precise reasoning, and prompt decision making under duress. The outcome of military nutrition research must be rations that are readily consumed in quantities sufficient to fuel maximum intellectual and physical performance. Thus, the question of whether underconsumption is reliably associated with measurable degradation in intellectual behavior is of considerable concern to developers of military rations.

1  

Mary Z. Mays, U.S. Army Medical Research and Materiel Command, Frederick, MD 21702-5012



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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations 15 Impact of Underconsumption on Cognitive Performance Mary Z. Mays1 Not Eating Enough, 1995 Pp. 285–302. Washington, D.C. National Academy Press BACKGROUND Conditions on the modern battlefield require that all soldiers be able to perform at their peak. Moreover, higher than normal levels of physical or intellectual performance may be required for long periods of time. Subtle deficits in intellectual behavior can dramatically degrade combat effectiveness, which requires sustained vigilance, precise reasoning, and prompt decision making under duress. The outcome of military nutrition research must be rations that are readily consumed in quantities sufficient to fuel maximum intellectual and physical performance. Thus, the question of whether underconsumption is reliably associated with measurable degradation in intellectual behavior is of considerable concern to developers of military rations. 1   Mary Z. Mays, U.S. Army Medical Research and Materiel Command, Frederick, MD 21702-5012

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations Military nutrition researchers have not taken this responsibility lightly. The history of American, Canadian, and British research on military rations is easily traced from the World War II era to the present. Rations have been studied in temperate, hot, cold, and high-altitude conditions. Experiments as early as the 1950s (Korean War era) were conducted by interdisciplinary teams of researchers who measured the spectrum of biochemical, physical, psychological, and social parameters (Johnson and Sauberlich, 1982). These investigators went to great effort to use state-of-the-art technologies in harsh field settings, just as investigators do now. Investigators then and now found it was possible to do extensive testing in the field, but difficult to hold extraneous variables constant. However, the vast majority of the studies were not designed to study the relationship of underconsumption to cognitive performance, per se, or the ability of military rations to sustain cognitive performance under stress. Underconsumption For the purposes of this review, underconsumption was operationally defined as a loss of gross body weight due to restrained eating, loss of appetite, or exertion. In all cases energy expenditure exceeded energy intake (underconsumption: kcal intake/kcal expended < 1.00). Failing to consume sufficient calories to maintain body weight (while in the presence of ample food) should be an anomaly, since under normal circumstances it is unlikely to have survival value. The circumstances under which it reliably occurs are riveting. Underconsumption should be particularly rare when the individual faces novel and strenuous work. For this reason, the soldier's underconsumption in field settings is especially intriguing. Although the camouflage-colored, armor-like packaging and shelf-stable, ready-to-eat engineering of military rations can easily explain a few days of underconsumption, they cannot explain the consistent finding that soldiers steadily lose weight when eating military rations for periods of 10 to 45 days (Askew et al., 1986, 1987; Carter et al., 1992; Hirsch et al., 1985; Johnson and Sauberlich, 1982; King et al., 1992; Popper et al., 1987; Roberts et al., 1987; Thomas et al., 1995; USACDEC/USARIEM, 1986). The boundary conditions of this phenomenon are as well established as its replicability. When soldiers were fed hot, cook-prepared, garrison-type meals in the field, they did not underconsume (Rose and Carlson, 1986), and when they were fed shelf-stable, ready-to-eat military field rations in a garrison-like environment, they did not underconsume (Hirsch and Kramer, 1993). Thus, the phenomenon of underconsumption is the result of an interaction between the field setting and the type of ration.

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations Note that although underconsumption leads to weight loss, it does not necessarily lead to nutritional deficiency. The quality of food and the absolute amount of food consumed may meet physiological minimums, and thus prevent disease, but not prevent weight loss. Military rations are calorie dense and vitamin fortified to ensure that they will be nutritionally adequate even when consumed in small quantities (Askew et al., 1987; Johnson and Sauberlich, 1982; Lichton et al., 1988; Moore et al., 1992; Shippee et al., 1994; Thomas et al., 1995). Cognitive Performance For the purposes of this review, cognitive performance was operationally defined as a score on a test of intellectual behavior (such as memory, reasoning, attention, vigilance, choice reaction time, arithmetic, or information coding). Cognitive performance is influenced by, and often confused with, psychomotor performance and mood. Psychomotor performance was operationally defined as a score on a test of skill or ability (such as sensation, perception, coordination, mobility, agility, reaction time, or pursuit tracking). Observations made by investigators or investigators' confederates about the cognitive or psychomotor performance of subjects were considered separately due to the subjective nature of such observations. Mood was operationally defined, in this review, as any self-report survey of cognitive performance, psychomotor performance, affective behavior, or nutrition-related symptoms. Interviews or standardized clinical tests of "personality," although designed to measure underlying traits, rather than transient states, were considered equivalent to self-report surveys of mood. Methodological Issues This section provides a context for the extant data and suggests the kind of experiments that need to be done in the future. The majority of studies reviewed for this paper were designed to test the nutritional adequacy and acceptability of military rations or field-feeding systems. The relationship of underconsumption to cognitive performance was not the main focus of the studies. These studies were not concerned with the degree of stress imposed by the field setting and how that stress might affect eating behavior or cognitive performance. The design of the experiments and the analysis of the results did not provide the opportunity to determine the relative contributions of underconsumption, the field setting, and the interaction (of underconsumption and the field setting) to changes in cognitive performance. Consequently,

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations these studies will not yield straightforward conclusions about cognitive performance. Despite this problem, they must be examined, because they constitute the only database on the effects of underconsumption on cognitive performance. Field Settings A variety of contextual factors present in the field setting reduce eating and sustain a pattern of underconsumption even when it is not adaptive (Hirsch and Kramer, 1993; Meiselman and Kramer, 1994). The engineering of military field rations contributes to underconsumption, no doubt, but it is likely that eating cold rations, eating during short breaks, eating by yourself, performing demanding physical exercise, and performing challenging intellectual tasks contribute far more. These conditions of the social and physical environment influence cognitive performance as well. Military field exercises (and combat deployments) dictate a dramatic change from daily routines. By necessity, they greatly restrict the activities of soldiers, limiting their ability to maintain a normal routine for relaxation, personal hygiene, and so on. Moreover, in any given field exercise, at least some of the following conditions are present: 24 h/d exposure to harsh climates, primitive latrines, minimal privacy (in mixed-gender and same-gender settings), separation from family, sleep loss, and danger. These conditions remove the normal discriminative cues that control a variety of behaviors and may increase free-floating anxiety. This kind of stress has been shown to disrupt cognitive performance (NRC, 1986) and to contribute to underconsumption (Hirsch and Kramer, 1993). Normative Data In order to separate the impact of underconsumption, per se, from the impact of the field setting, the baseline of normal cognitive performance must be adequately defined. Units often spend weeks preparing for a field-training exercise. In the days immediately prior to departure, soldiers are typically too busy to eat and sleep regularly. In many cases they experience a growing anxiety as they anticipate performance evaluation, the rigors of field living, the potential danger of the operation/exercise, or separation from family. Unfortunately, baseline data on cognitive performance were typically taken immediately before departure to a field-training site. Furthermore, baseline measurements were typically the first experience the soldier had with the specific cognitive tests. Low estimates of baseline cognitive performance might

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations have obscured the degree to which performance was actually degraded by underconsumption and the field setting. Control Group Data A second issue that surfaces whenever a study involves comparison against a baseline is the issue of whether a "practice effect" enhanced or attenuated the treatment effect. One approach to eliminating a practice effect was to use cognitive tests that required such common skills that no practice was required; that is, a test on which (in the absence of any experimental manipulation) performance typically shows little change over repeated trials. Another approach was to engage subjects in a large number of practice trials to ensure that performance was asymptotic. Yet another approach was to refuse to give subjects feedback on their performance so that they were unable to derive successful strategies for improving. Each of these approaches runs the risk of making the test relatively insensitive. Studies did not typically include a control group, which would allow a practice effect to be quantified or to serve as a covariate in the analysis of treatment effects. Furthermore, in order to separate the impact of underconsumption, per se, from the impact of the field setting, the field setting must be kept constant across a control group that does not underconsume and a treatment group that does. In many field-ration studies, the treatment group ate one field ration, while the control group ate another. They shared the same field setting, but both ate field rations, both underconsumed, and both lost weight. Thus, it was impossible to determine whether underconsumption, the field setting, or some interaction of the two influenced performance on cognitive tests. Cognitive Performance Tests The difficulty of defining the relationship between underconsumption and cognitive performance is brought into perspective by considering the difference between measuring body weight and measuring cognitive performance. Body weight can be measured simply, accurately, and reliably using commonly accepted methods. Moreover, the standard error of measurement on any given weighing instrument can be easily established and is quite small (± 0.1 percent) relative to what is considered a meaningful change in body weight (± 2.0 percent). In contrast, error in measurement on a given cognitive test is often equal to a meaningful change in performance. Similarly, regardless of whether weight loss is due to loss of water, fat, or muscle (or some unique combination of the three), change in body weight accurately reflects the total

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations loss. The total score on a battery of cognitive performance tests, however, may not accurately reflect the degree of change in one of the components comprising the battery. A long-standing and seemingly unresolvable controversy surrounds the search for an optimum set of tests of cognitive performance. The controversy has plagued numerous disciplines as disparate as intelligence testing (Scarr and Gallistel, 1993), military selection and classification (Butcher et al., 1990; Sperl et al., 1992), clinical neuropsychology (Kane, 1991; Matarazzo, 1992; Retzlaff et al., 1992), neurotoxicology and behavioral pharmacology (Iregen and Letz, 1992; Kane and Kay, 1992), as well as nutrition research (NRC, 1986). Over the last 50 years, military nutrition researchers have used individual tests, batteries of tests, obviously different tests, quite similar tests, the same tests in different media, and the same tests with different instruction sets. Environmental Conditions at Testing Because field-ration studies are by their very nature repeated-measures studies and because they are necessarily conducted in the context of an operational scenario, one of the most difficult aspects of the study to control is the context of performance testing. Factors such as the illumination, ambient temperature, availability of chairs and desks, time of day, and so on, often were not within investigators' power to control and varied dramatically across the different testing sessions within an experiment. All of these factors have been shown to influence performance on cognitive tests (Kane and Kay, 1992; Kreuger and Babkoff, 1992; NRC, 1986). This background noise probably realistically mimics the conditions for which the rations are designed. When the purpose of a study is to determine whether cognitive performance is grossly degraded by extended subsistence on a specific ration, the variance in extraneous variables is largely irrelevant. However, when the purpose of the experiment is to determine the degree to which a specific level of consumption influences cognitive performance, this variance reduces the ability to characterize the effect precisely. Performance Motivation Several field studies reviewed for this chapter described the remarkably high or low levels of motivation that soldiers brought to the experiment. In some cases, soldiers acted as though the experiment was a contest, with a winner to be declared at the end, and so performed well above normal limits. Conservely in other cases, soldiers expressed frustration with what appeared

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations to them to be pointless laboratory tests and so were unwilling to exert themselves. This problem is exacerbated by the fact that intact groups are used for treatment and control groups in most field-ration studies. That is, a platoon or company that has worked together for many months and has one role in the exercise is compared to another with a somewhat similar role. Not only does this influence the type of statistic that should be used in analyzing data, but it increases the probability that there will be several alternative explanations for experimental results. Whatever differences the groups bring to the experiment may interact in subtle and unpredictable ways with the experimental treatment. Furthermore, leaders have an unmistakable impact on soldier attitudes and performance during the experiment. Unless all unit leaders (1) understand and value the purpose of the experiment to the same degree, (2) articulate it equally well to their subordinates, and (3) place the same importance on compliance with the experimental protocol, the groups are likely to have very different levels of motivation. This is particularly true when there is no way to conceal from one group how it differs from another, as is the case when two very different rations are compared. One group may perform better than another or improve its performance over time due to a placebo or expectancy effect (Adair, 1973). Consideration of Individual Differences The range of weight change was quite large in many of the studies where there was an average weight loss (Askew et al., 1987; Hirsch et al., 1985; King et al., 1992; Popper et al., 1987; Thomas et al., 1995). That is, there were soldiers who gained weight, while the majority of their peers lost weight. Similarly, the range of performance on cognitive tests was quite large in some instances (Askew et al., 1987; Hirsch et al., 1985; King et al., 1992; Popper et al., 1987; Thomas et al., 1995). Some attention was devoted to post hoc analysis of data after separating test groups into subgroups of those who lost weight, those who did not, and those who gained weight, but results were equivocal. No systematic attempt has been made to identify individual differences (in experience, workload, food preference, metabolism, personality, etc.) that could account for the willingness or ability to consume sufficient rations to maintain weight or that could influence cognitive performance in these settings.

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations Investigator Bias Investigators have tended to underreport or denigrate changes in cognitive performance when their clinical judgment suggested that these changes were not purely cognitive or were likely to be reversed with simple refeeding. However, this begs the issue, since momentary inattentiveness or confusion can have fatal consequences in military field settings. Influence of Underconsumption on Cognitive Performance The literature on simple underconsumption of military rations is astonishingly consistent. In the absence of substantial mental or physical stress, weight losses of 6 percent or less over periods of 10 to 45 days produce no meaningful degradation in cognitive performance (Askew et al., 1986, 1987; Hirsch and Kramer, 1993; Hirsch et al., 1985; Johnson and Sauberlich, 1982; Lichton et al., 1988; Popper et al., 1987; Roberts et al., 1987; USACDEC/USARIEM, 1986). Moreover, moderate levels of underconsumption enhance cognitive performance for 3 to 15 days. This should not be surprising given that food deprivation has been a routine component of animal learning experiments for the last 50 years. The controversy over the role of food deprivation in learning consumed researchers for many years (Spence, 1956; Spence and Spence, 1967), but deprivation's ability to stimulate purposeful action is well-established and has obvious adaptive significance. Clearly, when consumption remains above 50 percent of what is required, deficits in cognitive performance are minor even when underconsumption continues for weeks (Keys et al., 1950). Not so clear is what happens when consumption falls below 50 percent; apparently the rate of decline in cognitive performance is steady and significant (Shippee et al., 1994). Food deprivation is a special case of underconsumption. Individuals may consume 100 percent of what is available, but because an inadequate amount of food is available, they suffer the same consequences as those who "voluntarily" underconsume. The classic study of food deprivation was conducted by Keys et al. (1950). It was designed to deliberately induce a slow but steady, and eventually severe, loss of weight. It serves as a benchmark against which to measure the consequences of severe underconsumption in the absence of other stressors. Their data show little indication of meaningful changes in the cognitive performance of the group, although subjects repeatedly reported memory lapses, inability to concentrate, obsessive behaviors, apathy, and lethargy. Case study accounts of participants in the Keys et al. study (Schiele and Brozek, 1948) verified psychiatric deterioration

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations in 25 percent of the subjects. Post hoc analyses of accounts of behavior during famines (Graham, 1993; Keys et al., 1950; NRC, 1986), as well as popular accounts of men lost at sea and prisoners of war confirm that noncognitive behaviors of lethargy, helplessness, and hypochondria disrupt cognitive performance but do not prevent individuals from functioning in an intelligent and purposeful, even heroic, manner when the opportunity arises to procure food or escape the situation. A series of studies conducted in the 1960s evaluated the combined effects of restricted intake and exercise (Consolazio et al., 1967, 1968; Johnson et al., 1971). Fasting for 10 days produced severe malaise, abnormal electroencephalograms, and lapses in memory and alertness. A diet of 420 kcal of carbohydrate per day for 10 days also produced abnormal electroencephalo-grams, while a diet of 500 kcal of carbohydrate and protein per day for 10 days did not. Johnson and Sauberlich (1982) reviewed a series of American, British, Canadian, and Australian studies of the minimum number of calories per day needed to sustain military performance while on 4- to 14-d patrols in temperate and extreme environments. These studies are a testimony to the resilience of cognitive and psychomotor behavior. For example, Crowdy et al. (1982) studied the impact of 12 days of underconsumption on soldiers during arduous training and testing in the Malaysian jungle. The control group's average energy intake (kcal) was 82 percent of their energy expenditure (kcal), and the food-deprived group's intake was 47 percent, creating rapid weight losses of 3 percent and 6 percent, respectively. Performance on marksmanship, vigilance, arithmetic, and coding tests did not significantly change from baseline across the 12 d of testing, nor did it differ significantly between the groups. In contrast, studies of dieters and restrained eaters (Green et al., 1994; Rogers and Green, 1993; Rogers et al., 1992) and studies of individuals suffering from bulimia nervosa or anorexia nervosa (Jones et al., 1991; Laessle et al., 1990; Szmukler et al., 1992) suggest that underconsumption combined with other stressors significantly degrades cognitive performance. The training of special operations forces combines food deprivation with several stressors, including exercise, sleep deprivation, danger, and personal evaluation (Hudgens et al., 1992; Marriott, 1993; Moore et al., 1992; Opstad et al., 1978; Pleban et al., 1990; Tognum et al., 1986; Shippee et al., 1994). Under these circumstances cognitive performance degradation (from 5 percent to 35 percent below baseline) occur within a few days, although it is not clear what role underconsumption, by itself, plays in including these deficits.

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations PROPOSED RELATIONSHIP OF UNDERCONSUMPTION TO COGNITIVE PERFORMANCE Based on their extensive review of the literature on starvation, Keys et al. (1950) estimated the rate of weight loss that could be expected over time as a function of underconsumption. Their estimates have been confirmed over the years in a variety of settings, including military field settings. Figure 15-1 illustrates their predictions concerning weight loss over a 60-d period. The simplest hypothesis for the relationship of underconsumption to cognitive performance would be to suggest that it corresponds to the relationship of underconsumption to weight loss. That is, for each X percent drop in consumption, there would be a predictable Y percent degradation in cognitive performance. However, data from two thorough studies of underconsumption (Keys et al., 1950; Shippee et al., 1994) suggest that the relationship is not so simple. Figure 15-2 summarizes the change reported over time in cognitive performance and body weight in these two studies (both dependent measures are expressed as a percent of baseline to facilitate direct comparison). Subjects in the Keys et al. (1950) study did not show meaningful decrements in cognitive performance, even when weight loss was substantial. Soldiers in Ranger training experienced significant changes on similar measures of cognitive performance with a similar degree of weight loss (Shippee et al., 1994). These differences could be interpreted as evidence that the high degree of physical and mental stress inherent in Ranger training degrades cognitive performance, but food deprivation does not. However, consideration of all the extant data suggests that the expected value lies somewhere in between semistarvation data gathered in the Keys et al. study and the Ranger data. That is, even though a precise comparison of results across the studies reviewed for this paper was not possible, a general pattern of results did emerge. This pattern is illustrated in Figure 15-3. Underconsumption, in contrast to undernutrition, leads to energy deficiency rather than disease. Thus, mild to moderate underconsumption of nutritionally-fortified military field rations should lead to transient inattentiveness, indifference, and confusion rather than severe lapses in reasoning, comprehension, or memory. Substantial deficits in cognitive performance could occur, however, if other factors in the field setting interact with underconsumption (Askew et al., 1987; Colloway, 1982; Cohen et al., 1982; Gorsky and Calloway, 1983; Keys et al., 1950; Krueger and Bobkoff, 1992; NRC, 1986; Shippee et al., 1994; Webb, 1982).

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations FIGURE 15-1 Weight loss as a function of consumption over days. SOURCE: Developed from data published in Keys et al. (1950).

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations FIGURE 15-2 Relationship of cognitive performance to weight loss over days in two experiments. 1 = mean performance on tests of memory, reasoning, and spatial perception for subjects in a semistarvation study (adapted from data published in Keys et al., 1950); 2 = mean performance on tests of memory, reasoning, and spatial perception for soldiers in Ranger training (adapted from Shippee et al., 1994); 3 = mean body weight for soldiers in Ranger training (adapted from Shippee et al., 1994); 4 = mean body weight for subjects in a semistarvation study (adapted from Keys et al., 1950).

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations FIGURE 15-3 Proposed relationship of cognitive performance to consumption over days.

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations CONCLUSIONS AND RECOMMENDATIONS Given the methodological issues discussed, the value of Figure 15-3 lies primarily in its ability to generate discussion, rather than its accuracy as a summary of extant data. The apparent robustness of cognitive performance in the face of 5 to 10 percent losses in body weight over the course of 10 to 45 days may be genuine or may be attributable to experimental designs which failed to (1) account for the contextual cues present in field settings, (2) accurately define baseline performance, (3) provide an appropriate control group, (4) hold testing conditions constant, (5) assess motivation levels, and (6) analyze individual differences. If this robustness is genuine, it would appear that there is no practical significance to the underconsumption typically seen among soldiers subsisting entirely on military rations. However, the problem in accepting mild to moderate underconsumption lies in the fact that combat is fraught with emotional, mental, and physical stressors. Field studies that mimic these circumstances suggest that underconsumption exacerbates deficits in cognitive performance created by the situation. In that case, methods to reduce underconsumption could sustain and enhance combat effectiveness. The available data do not unequivocally answer the question of whether underconsumption seriously degrades cognitive performance. More importantly, they do not provide the military leader with sufficient information to weigh the cost of measures designed to increase consumption (taking time for regularly scheduled meals, heating food, eating in social groups, etc.) against the potential benefit (enhanced combat effectiveness). Just as the Army has doctrine about water discipline and work-rest cycles, which are couched in terms of the number of casualties they can prevent, the Army needs doctrine delineating the benefits of food discipline. A series of carefully designed dose-response field studies need to be conducted for the sole purpose of defining the increase in cognitive performance that can be derived from a specific level of consumption. In summary, the following conclusions can be drawn from military nutrition field studies: Weight losses of 6 percent or less over a period of 10 to 45 days produce no meaningful degradation in cognitive performance. Consumption levels of 75 percent to 90 percent of requirements may enhance cognitive performance in the first 3 to 15 days. Consumption of 50 percent or less of requirements will significantly degrade cognitive performance, especially when combined with forced exercise and sleep deprivation.

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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations The available data do not provide sufficient information to develop a food-discipline doctrine that could be used to sustain cognitive performance under stress. A field study designed specifically to assess the relationship between specific levels of consumption and cognitive performance could form the basis for an effective food discipline doctrine. REFERENCES Adair, J.G. 1973. The Human Subject: The Social Psychology of the Psychological Experiment. Boston, Mass.: Little, Brown. Askew, E.W., J.R. Claybaugh, S.A. Casinell, A.J. Young, and E.G. Szeto 1986. Nutrient intakes and work performance of soldiers during seven days of exercise at 7,200 ft altitude consuming the Meal-Ready-to-Eat Ration. Technical Report T3-87, AD A176 273. Natick, Mass.: U. S. Army Research Institute of Environmental Medicine. Askew, E.W., I. Munro, M.A. Sharp, S. Siegel, R. Popper, M.S. Rose, R.W. Hoyt, J.W. Martin, K. Reynolds, H.R. Lieberman, D. Engell, and C.P. Shaw 1987. Nutritional status and physical and mental performance of special operations soldiers consuming the Ration, Lightweight or the Meal, Ready-to-Eat Military Field Ration during a 30-day field training exercise. Technical Report T7-87, AD A179 553. Natick, Mass.: U. S. Army Research Institute of Environmental Medicine. Butcher, J.N., T. Jeffrey, T.G. Cayton, S. Colligan, J.R. Devore, and R. Minegawa 1990. A study of active duty military personnel with the MMPI-2. Milit. Psychol. 2(1):47–61. Calloway, D.H. 1982. Functional consequences of malnutrition. Rev. Infect. Dis. 4:736–745. Carter, J.S., M.H. Ezell, W.R. Barfield, and L.H. Anderson 1992. Anthropometric, psychomotor, and hemodynamic changes during twenty-one continuous days of eating only Meals, Ready-to-Eat (MREs). Milit. Med. 157(10):537–539. Cohen, R.M., H. Weingartner, S. Smallberg, and D.C. Murphy 1982. Effort in cognitive process in depression. Arch. Gen. Psychiat. 39:593–597. Consolazio, C.F., L.O. Matoush, H.L. Johnson, R.A. Nelson, and H.J. Krzywicki 1967. Metabolic aspects of acute starvation in normal humans (10 days). Am. J. Clin. Nutr. 20:672–683. Consolazio, C.F., L.O. Matoush, H.L. Johnson, H.J. Krzywicki, G.J. Isaac, and N.F. Witt 1968. Metabolic aspects of calorie restriction: Hypohydration effects on body weight and blood parameters. Am. J. Clin. Nutr. 21:793–802. Crowdy, J.P., C.F. Consolazio, A.L. Forbes, M.F. Haisman, and D.E. Worsley 1982. The metabolic effects of a restricted food intake on men working in a tropical environment. Hum. Nutr. Appl. Nutr. 36A:325–344. Gorsky, R.D., and D.H. Calloway 1983. Activity pattern changes with decrease in food energy intake. Hum. Biol. 55:577–586. Graham, G.G. 1993. Starvation in the modern world. N. Engl. J. Med. 328(14):1058–1061. Green, M.W., P.J. Rogers, N.A. Elliman, and S.J. Gatenby 1994. Impairment of cognitive performance associated with dieting and high levels of dietary restraint. Physiol. Behav. 55(3):447–452.

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