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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations 14 When Does Energy Deficit Affect Soldier Physical Performance? Karl E. Friedl 1 Not Eating Enough, 1995 Pp. 253–283. Washington, D.C. National Academy Press During the last month of the siege men at fatigues, such as trench-digging, after ten minutes' work had to rest a while and go at it again; men on sentry-go would drop down from syncope (the spell of duty had to be reduced to one hour instead of two); those carrying loads would rest every hundred yards or so. Observations on the effects of restricted rations on British and Indian soldiers during the 1915–1916 Siege of Kut (Hehir, 1922, p. 867). INTRODUCTION Several decades ago, Army nutritionists concluded that soldiers could maintain normal work capacity during short periods (< 10 days) of severely restricted intakes (Consolazio et al., 1967, 1979). This finding corroborated the conclusions from longer-term studies conducted at the University of Minnesota that an energy deficit resulting in less than 10 percent loss of body weight 1 Karl E. Friedl, Army Operational Medicine Research Program, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD 21702-5012
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations does not impair physical performance (Taylor et al., 1957). There is a long history of such Army-sponsored research on performance decrements related to energy-deficient diets that reaches back to laboratory studies from the University of Minnesota in the 1940s and 1950s (for review, see Grande, 1986) and field studies conducted by the U.S. Army Medical Research and Nutrition Laboratory in the 1960s and 1970s (for review, see Consolazio, 1983). In the past decade, the Occupational Physiology Division at the U.S. Army Research Institute of Environmental Medicine has repeatedly performed physical testing during ration studies (e.g., Askew et al., 1987; Moore et al., 1992; Teves et al., 1986). The data from these more recent studies have been largely overlooked because of the general absence of findings of performance decrements. These negative findings could be the result of protocols failing to produce an actual energy deficit or because the tests used were insensitive to real performance decrements. However, after these and other interpretations of the data are considered, the conclusion of this chapter will be that militarily relevant physical performance appears to be well sustained through the range of voluntarily low intakes (underconsumption) of modern military rations. If underconsumption occurs for sufficient duration it will unquestionably produce deficits in physical performance. Changes in the oxidative capacity of muscle, the oxygen carrying capacity of the blood, and the mass of metabolically active tissue probably account for most of the observed decrease in aerobic capacity, which in turn, explains reduced stamina and physical work capacity (Keys et al., 1950; Spurr, 1986). Loss of skeletal muscle, changes in muscle biochemistry, and changes in the balance of muscle fiber types produce reductions in dynamic strength (Henriksson, 1990; Taylor et al., 1957). Such decrements in physical performance have been established at extreme levels of underconsumption in the 1950 Minnesota Starvation Study and in studies of soldiers in the U.S. Army Ranger course (Johnson et al., 1976; Moore et al., 1992 [Ranger I]; Shippee et al., 1994 [Ranger II]). These levels of underconsumption were voluntary only in the sense that the participants could quit the programs; if offered more food, these men would have readily consumed it. However, these studies are important for this book because they illustrate an extreme of underconsumption, which permits interpolation of the effects of the more pertinent (i.e., modest) energy deficits. A different militarily relevant extreme of underconsumption—very high deficits for a short period of time—will also be addressed.
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations ASSESSING UNDERCONSUMPTION Baseline Nutritional Status A typical, fit, young male soldier weighs about 75 kg, and 15 percent of this weight is fat. These fat energy stores are adequate to fuel the soldier for a 1,000 kcal deficit per day lasting for about 75 days; beyond this point, energy deficits will be made up primarily from organ and muscle protein as the soldier enters an advanced stage of starvation. A certain proportion of lean mass, usually about one-third of the total weight change, is lost or gained along with changes in storage fat (Forbes, 1993), but as fat stores become increasingly scarce with a severe weight loss, this proportion increases. This was illustrated in the Ranger-I study (Moore et al., 1992) where an increased proportion of the lean tissue contributed to overall weight loss between 6 weeks (30 percent) and 8 weeks (40 percent). At the end of the 8-wk study, soldiers had lost an average 16 percent of body weight, and the majority of men were on the brink of a metabolic transition to severe starvation because they had little or no fat stores remaining (Friedl et al., 1994). This metabolic threshold also appeared to coincide with the approach of a psychological limit to voluntary participation, a point recognized by the Ranger Training Brigade commander by the number of soldiers who were disqualified near the end of the course for food violations (see Appendix 1 in Moore et al. ). Thus, the paradigm of Ranger-I, a 1,200 kcal deficit per day for 60 days, appears to define an extreme limit of voluntary underconsumption for contemporary male soldiers. Current-day soldiers can better tolerate an energy deficit (in terms of preserving performance) because they are better nourished and begin with more fat-free mass than the soldiers of earlier eras. This point is illustrated by a wartime example that involved apparently modest weight losses but resulted in profound physiological consequences. In the winter of 1915, 15,000 British and Indian soldiers were surrounded by Turkish troops at Kut in southern Mesopotamia; they surrendered when their rations were depleted 5 months later. By the time of surrender, intake for the British soldiers had been reduced to half of the estimated normal 3,600 kcal/d (Hehir, 1922). Weight loss averaged 10 and 14 percent of weights measured near the start of the siege for the British and Indian soldiers, respectively. Although these losses are not even as large as the relative weight loss observed in Ranger-I, the restriction had a greater impact on the average soldier than that observed in the Ranger studies. The chief medical officer recorded that ''the present condition of the average officer and fighting man…is much below par in stamina, and, without feeling any decided weakness, he is incapable of doing anything approaching the
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations normal amount of physical or mental work" (Hehir, 1922, p. 869). Numerous starvation deaths occurred before the surrender of the garrison. The first point to be made from this example is that relative weight losses cannot be meaningfully compared unless the initial nutritional status is also considered. The soldiers at Kut were already at reduced weight from earlier fighting and a long march to Kut. More importantly, even at baseline, soldiers of this earlier era were not as well nourished as current-day soldiers. U.S. soldiers today have an average of 20 lb (9.1 kg) more body weight, including 15 lb (6.8 kg) more lean mass, than U.S. soldiers in World War I, and approximately 10 lb (4.5 kg) more than World War II soldiers (Friedl, 1992). A large loss of body weight (˜10 percent) in these soldiers with initially lower body fat stores and muscle mass could be a much more severe physiological challenge than it would be for typical modern-day, well-nourished soldiers. Consistent with this hypothesis, soldiers who began training with very low body fat (< 10 percent) in the Ranger-I study were less likely to succeed than were slightly fatter soldiers (Moore et al., 1992). Current-day soldiers also receive nutrition of better quality than their earlier counterparts. The soldiers at Kut did not have a vegetarian Multi-Faith Meal (MFM), and at least 1,000 Indian soldiers who would not eat horseflesh were diagnosed with scurvy. They did not have rations carefully constructed to meet military recommended daily allowances (MRDAs) and to provide a balanced intake even in situations involving high stress and restricted intake. Many of the British soldiers suffered from beriberi with symptoms of degraded work ability superimposed on the problem of a deficient energy intake. These are problems that soldiers should no longer face. For example, in the recent Ranger studies, even in the face of a large average energy deficit over 2 months, no substantial vitamin, mineral, or nutrient deficiency could be established even when soldiers were subsisting on only one Meal, Ready-to-Eat (MRE) or one Long Life Ration Packet (LLRP) per day (up to 10 days continuously). Thus, comparisons to earlier studies must take into account the underlying baseline nutritional status. Overnourished Soldiers Improvements in nutrition during this century have led to an increase in the proportion of overnourished soldiers. Thus, any study of the consequences of underconsumption must be carefully interpreted with respect to the number of soldiers who could well afford an energy deficit and particularly with respect to those soldiers who may be actively attempting to lose weight. In the 1991 study of the nutritional adequacy of the MRE compared to hot rations during field training, overweight men deliberately attempting to lose weight
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations emerged as a significant confounding factor in the data analysis (Thomas et al., 1995). Fortunately, at the start of the study the investigators had asked who was trying to lose weight. One-third of the MRE test group was trying to lose weight and achieved a loss of 4.4 kg (4.8 percent of initial body weight; n = 13), compared to 2.3 kg (or 3.1 percent weight loss; n = 22) for the remainder of the group (Thomas et al., 1995). This weight loss was appropriate for men averaging a robust 26.5 ± 3.8 percent body fat2 (compared to 18.2 ± 4.8 percent for the men not intending to lose weight). There was no indication from detailed nutritional and clinical serum biochemical tests that health or nutritional status was adversely affected with this weight loss, nor was there any indication that performance suffered (Thomas et al., 1995). Another recent study investigated body composition changes in young female basic trainees eating without restriction (Westphal et al., 1995). This study revealed that at least one-fourth of the women exceeded Army body fat standards at the start of basic training. Despite an average intake of 2,600 kcal/d, this fattest group of women, averaging 36 ± 3.8 percent body fat2, lost weight (0.5 ± 3.2 kg). However, the true magnitude of the body composition changes is overlooked if only reported as change in body weight; this group gained 1.7 ± 1.8 kg of fat-free mass at the same time they lost 2.2 ± 2.7 kg of fat (3 percent of body weight). Despite this loss of fat weight, the physical performance of these women was markedly improved at the end of basic training (Sharp et al., 1994; Westphal et al., 1994). This improved performance included an increased muscular endurance demonstrated by large improvements in push-up and sit-up ability, increased strength marked by an average increase of 10 lb (4.5 kg) in maximal lift capacity, and improved aerobic capacity indicated by an average 5-min reduction in 2-mi run times. These recent studies of men (the MRE study) and women (the study of basic trainees) highlight the problems in evaluating the effect of field rations in modern-day overnourished soldiers. Voluntary underconsumption and/or some loss of fat weight in these subgroups are not necessarily harmful. There is even evidence that some aspects of physical performance will be improved. In an earlier Committee on Military Nutrition Research report, Kirk J. Cureton provided compelling evidence that the loss of excess fat weight can indeed enhance various types of physical performance, most notably run time (Cureton, 1992). 2 Percent body fat in these studies was measured by whole body scan using duel-energy x-ray absorptiometry.
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations Nutritional Status of Female Soldiers Although women have not been studied during extreme conditions such as those in the Minnesota Starvation Study or Ranger training, there is evidence to suggest that physical performance could be better maintained by female soldiers. This conclusion is based, in part, on a superior nutritional status in the form of larger gender-appropriate fat stores. A typical, young female soldier weighing 60 kg with 30 percent body fat carries sufficient storage fat to survive an energy deficit for approximately twice as long as her male counterpart. This hypothesis is corroborated by numerous wartime studies demonstrating the disproportionate survival of women over men during periods of extreme starvation (Brozek et al., 1946; Burger et al., 1948). Greater fat stores are only part of the advantage; at a comparable exercise level, women utilize fat energy better than men (Nygaard, 1985), and because of lower lean body mass relative to men, women have lower basal metabolic requirements. Although female soldiers may hold a theoretical advantage during caloric restriction, and performance may improve rather than degrade with the loss of fat weight, underconsumption of rations produces a performance risk in women that is not encountered in men. Premenopausal women with restricted intakes are likely to encounter deficiencies of minerals and nutrients related to red cell formation (iron and folate). This increased potential for iron-deficiency anemia also leads to compromised work capacity (Finch and Huebers, 1982), as demonstrated by detailed studies performed on Sri Lankan tea leaf pickers (Edgerton et al., 1979; Gardner et al., 1977). In one study of these workers, all women with serum hemoglobin over 13 g/dl could complete an 18-min graded treadmill test, but fewer than half of the women with less than 12 g/dl could complete the same test (Gardner et al., 1977). The relationship between iron intake and performance was demonstrated with iron supplementation, where the effect could be calculated as a 0.75 kg increase in tea picked per day per gram of hemoglobin increase per dl of serum (Edgerton et al., 1979). Thus, work performance can be influenced by iron deficiency even within the clinically normal range for hemoglobin. This problem of iron deficiency in women has direct relevance to U.S. servicewomen. Most recent studies of female soldiers indicate a large proportion of women to be only marginal for iron balance (King et al., 1993; Westphal et al., 1994). Inadequate intakes related to weight-loss attempts are responsible for at least some of this imbalance. In the 1989 West Point Nutritional Survey (Klicka et al., 1993), 80 percent of female cadets stated that they were attempting to lose weight. Measured nutrient intakes confirmed restricted caloric intakes, with at least 10 percent of cadets taking in less than 1,700 kcal/d (i.e., < 70 percent of the 2,400 kcal/d female MRDA for energy). Even when iron supplement use is included in the estimates, one-third of
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations female cadets had iron intakes below the MRDA of 18 mg/d. One-third of the women sampled had hemoglobin levels of less than 12 g/dl of serum (Friedl et al., 1990), a point of diminished work capacity in the Sri Lankan women in Gardner et al.'s study (1977). The results of the West Point study suggest that women consuming less than 2,000 kcal/d at conventional nutrient densities may not take in sufficient iron and folacin to maintain optimal performance. The effect of reduced hemoglobin (< 12 g/Dl) on performance has been recently demonstrated in young women in Army basic training. The women with lower hemoglobin concentrations had 2-mi run times that were 1 to 11/2 minutes slower than the others (Westphal et al., 1995). Male cadets in the West Point study did not demonstrate problems with iron, and male soldiers do not develop signs of iron or other mineral deficiencies even during intensive training with reduced intakes observed in the Ranger course (iron intake averaged 13 mg/d over 2 months) (Moore et al., 1993). Thus, single nutrient deficiencies do not appear to be a concern in male soldiers, where the only compromise from restricted military rations is an energy deficiency. ASSESSING PERFORMANCE Work Capacity and Energy Expenditure The importance of adequate intake to work productivity (i.e., voluntary energy expenditure) can be demonstrated when energy deficits are high or prolonged, specifically because additional calories will be readily consumed when offered, and productivity will increase (for extensive review, see Consolazio, 1983; Spurr, 1986, 1990). Thus, the circumstances are somewhat different from the problem of voluntary underconsumption. For example, coal and steel production in German factories during World War II fell off with the reduction in energy intakes as food supplies diminished, particularly when average intakes decreased from 2,200 kcal/d to 1,800 kcal/d (Consolazio, 1983). When the rations of a group of young coal miners increased from 2,800 to 3,200 kcal/d, production increased from 7 to 9.6 tons of coal per day per man; an additional 400 kcal/d produced a small additional increase in productivity (Kraut and Muller, 1946). Such studies suggest that voluntary work output can be limited by restricted daily intake. Spurr has demonstrated an energy "ceiling" effect produced by chronic underconsumption. Using continuous heart rate monitoring, he showed lower average energy expenditures in undernourished Columbian boys mixed into a group of normal Columbian boys in a summer sports program. For several hours following a hot lunch, heart rates did not differ between the groups.
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations However, after that time heart rates fell off in the undernourished group (Spurr and Reina, 1988). Although other factors such as mood and morale may contribute to these phenomena, the reduction in physical work capacity is most probably related to reduced energy stores, including low body fat and perhaps inadequately replenished muscle glycogen (Karlsson and Saltin, 1971). Ranger students present a variation where a sustained physical effort is not optional, demonstrating behavioral and metabolic adaptations to accommodate the reduction in energy intake while maintaining the required level of effort. By the end of Ranger training, soldiers move with great deliberation and visibly demonstrate no wasted motion. There is also a marked reduction in circulating thyroid hormones and an increased sensitivity to cold, even in summer classes, which suggests the same reduction in cellular metabolism that has been measured in earlier studies such as the Minnesota study. Even Major General Sir Hehir (1922) demonstrated reduced body temperatures in his 1916 observations of semi-starved soldiers. Results of increased feeding in this setting appear to be split between contributions to reducing the energy deficit (reducing the rate of catabolism of body energy stores) and increasing energy expenditure (raising the "ceiling"). In the Ranger-I study, energy expenditure estimated from changes in body composition and estimated intakes indicated an average energy deficit of 1,200 kcal/d and a total energy expenditure of 4,000 kcal/d (Moore et al., 1992). When the intakes were increased by 400 kcal/d in the Ranger-II study (Shippee et al., 1994), the deficit was reduced to 1,000 kcal/d, implying also an increase in energy expenditure to approximately 4,200 kcal/d (Figure 14-1A). However, the attenuated decline in triiodothyronine when the soldiers were given more food suggests that it was basal metabolic functions (e.g., body heat production) that were better sustained with the small increase in rations (Figure 14-1B). This result does not necessarily signify an increase in productive work. After 24 weeks of semistarvation in the Minnesota study at nearly half of normal intakes, resting energy expenditure had declined by 40 percent. Although the majority of this decline was explained by the reduction in body cell mass, a portion of the reduction (15–25 percent) was attributed to reduced cellular energy requirements (Keys et al., 1950). In shorter-term studies, Grande et al. (1958) concluded that most of a decrease in resting metabolic rate was due to the decline in cellular metabolic rate, with no more than one-third of the decrease accounted for by loss of cell mass. An even greater savings in energy expenditure (accounting for approximately 1,000 kcal/d) in the Minnesota Starvation Study came from reductions in voluntary activity. These studies suggest several mechanisms, such as increased economy of movement and decreased resting metabolic rates, through which soldiers who are voluntarily underconsuming might demonstrate a reduction in energy expenditure
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations FIGURE 14-1 Daily intakes (A) are represented for soldiers through the four phases of training in the Ranger-II study. Dashed horizontal lines indicate the average daily energy intake and expenditure of the Ranger-I study, with a deficit of 1,200 kcal/d; solid lines indicate the effect of +400 kcal/d intake in Ranger-II, with a reduction in the deficit (to 1,000 kcal/d) and an increase in the total daily energy expenditure. This increased intake in Ranger-II was adequate to maintain normal circulating levels of triiodothyronine (B), which suggests a more normal metabolic rate, but not necessarily a change in soldier work capacity or productivity.
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations without necessarily decreasing productive work. However, the early responses to restricted energy intake in a normal subject do not include a change in resting metabolic rate; instead there is an increased utilization of body fat, reflected in weight loss and a change in the respiratory quotient. Note that in all of these more extreme examples, including wartime coal miners, undernourished Columbian children, Army Ranger students, and volunteers in the Minnesota Starvation Study, all would have willingly consumed more calories, if they were offered. In normal circumstances, it is assumed that appetite would increase energy intakes following voluntary underconsumption before energy expenditure is noticeably affected. At least at the extreme level of deprivation of Ranger students, there was a strong hunger drive even in the face of multiple stressors. Specific Tests of Performance The measurement of physical performance end points is not a trivial task in the context of military field studies. Unlike the picking of tea leaves or cutting of sugarcane, most military work does not readily lend itself to quantification through measurement of a single end product that signifies productivity. A few studies have successfully tested work productivity, such as a recent examination of the metabolic costs of a sustained-operations howitzer firing simulation, where the number of rounds loaded and fired could be assessed over discrete periods of time (Sharp and Vogel, 1992). However, as it is difficult to measure work productivity in military field settings, operational rations have been typically assessed for their effects on specific work capabilities. The specific types of physical performance expected of soldiers in different specialties have been previously characterized. A 1980 review of the specific fitness requirements of each Military Occupational Specialty (MOS) categorized all MOSs into one of five combinations of strength and aerobic demands (Vogel et al., 1980). Strength was a key aspect of many MOSs, but high aerobic demand (> 11.25 kcal/min) only occurred in association with high strength demands (> 40 kg lifted to waist height). There was no job specialty where the performance typical of a trained distance runner would be favored; thus, an appropriate evaluation of militarily relevant physical performance must involve more than aerobic fitness and, most importantly, should include strength assessments. Tasks that represent realistic job requirements in these different categories have been constructed but are generally too complicated and difficult to control for the assessment of adequacy of rations. A representative task for the most demanding cluster of MOSs (e.g., infantryman) was "carry a 45-kg bag for 1
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations km in 20 minutes"; a less-demanding MOS task (e.g., supply clerk) would require a soldier to "lift and carry 27 kg for 15 m, 40 times per hour." As a test becomes more complex, individual skill and motivation increasingly confuse interpretation of the tests, and test conditions may be more difficult to duplicate between sessions. The significant disadvantage of using these tasks as the end point measurement in a field study is that nothing is learned about the mechanism of the performance decline. Well-validated tests that assess different types of performance (with dependence on different energy sources) such as strength, muscular endurance, and aerobic capacity can better address nutrition questions and pinpoint the nature of the deficit. Many studies have used expedient tests such as handgrip strength or scores on the Army Physical Fitness Test (APFT); unfortunately, these are not the tests of choice for a nutrition study. Maximal handgrip is used as an indicator of strength, but it lacks the desirable sensitivity to changes in nutritional status, as will be further discussed. Push-ups and sit-ups from the APFT reveal something about muscular endurance but are also somewhat dependent on strength, and they do not optimally isolate muscle groups of interest. The third test of the APFT, the 2-mi run, is a good surrogate measure of aerobic capacity (Daniels et al., 1984; Mello et al., 1988). The correlation between 2-mi run time and maximal oxygen uptake can be as high as r = 0.9, with a narrow standard error of ~ 3 ml/kg/min (Mello et al., 1988). This measure is the most useful of the "expedient" tests, if a good effort can be obtained from volunteers in the test. Purer tests of physical capacity, which at least differentiate muscle energy sources, such as a dynamic lift test for strength, the Wingate test (30 seconds of maximal cycling exercise against a relative resistance) for anaerobic power, and a treadmill test to exhaustion for maximal aerobic capacity, can be carefully monitored and reproduced in a standardized way (see Vogel, 1994). A variety of factors must be considered in choosing the most appropriate physical performance tests for military field studies: Relevance to military task performance should be established. Type of performance must rely on energy sources of interest. High skill component may reduce the validity of repeated testing. One must be able to monitor the effort of individual subjects. Expedience of the test determines how many subjects can be tested. Safety of the test is critical to avoid injury and so that subjects can confidently give a best effort. An important aspect of physical test selection is to use expedient tests that are reasonably reproducible and that soldiers may be willing to perform in a consistent manner. Tests with a large learning curve are generally unsuitable,
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations higher requirements for several-day periods may occur, such as 6,000 kcal/d during 1 week of mountain training in the Ranger course (Moore et al., 1993), at least 5,500 kcal/d for the 5-d U.S. Navy Sea, Air, and Land (SEAL) trainee "hell week" (Smoak et al., 1988), 5,300 kcal/d in Zimbabwean recruits during dry hot-weather operations (MJR Kaka Mudambo, Zimbabwe Defense Forces, unpublished results using doubly labeled water, 1994), and greater than 8,000 kcal/d in the 5-d Norwegian ranger course involving little or no sleep (Opstad and Aakvaag, 1981). It is questionable whether calorie intakes that are better matched to energy expenditure have any demonstrable benefit in these highest energy expenditure scenarios. Compared to longer-term undernutrition, this direct-action scenario presents a different set of physiological limiters to physical performance. It is unlikely that even lean men will exhaust available fat energy stores in this period of time (a soldier with 10 percent body fat working at an exceptionally high 10,000 kcal/24 h for 5 days would not exhaust body energy stores). Instead of a gradual loss of lean mass to feed a chronic energy deficit, the problem is one of maintaining muscle function during high-intensity work without pausing for an appropriate rest phase ("overtraining"). For example, in Japanese rangers in a 93-h exercise (30- to 40-kg loads, 50-km travel in mountainous terrain, sleep < 3 h/d, consuming ~600 kcal/d), a marked increase in skeletal muscle enzymes indicates changes in muscle metabolism in response to the new level of strenuous work; however, there is only a small increase in myoglobin which suggests that this does not reflect actual muscle cell damage or catabolism (Kosano et al., 1986). Other examples of decrements in physical performance during continuous operations also suggest an overtraining phenomena related to higher-than-usual work loads. This effect has been observed in a study of 8-d continuous field artillery operations (Legg and Patton, 1987) and a 5-d scenario also involving upper body exertion such as load carriage (Murphy et al., 1984); in both cases, with minimal weight losses, upper body muscular strength and endurance significantly decreased. In another 8-d field artillery scenario with somewhat lower work levels, no decrements were observed (Patton et al., 1989). Acute "overtraining" effects may also include depletion of energy sources, which may not be restored to initial levels simply by increasing carbohydrate consumption (Jacobs et al., 1983). Thus, this is a special subset of the underconsumption problem that does not appear to benefit from increasing consumption. In fact, whether or not soldiers deprive themselves of food for a 3- to 5-d direct-action mission probably has little effect on their short-term performance, as long as they ingest sufficient carbohydrate to prevent ketosis and obtain adequate mineral supplements to replenish losses (Krzywicki et al., 1979; Taylor et al., 1954).
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations Norwegian Ranger Training: Intensive Training with Large Energy Deficits Male cadets from the Norwegian Military Academy participate in a 5-d ranger course as part of their training program. This course typically involves little or no sleep, and daily energy expenditure has been estimated to be greater than 10,000 kcal (Opstad and Aakvaag, 1981). When the cadets receive 1,500 kcal/d, they typically lose 4 to 5 percent of body weight and demonstrate a shift to an increased fat energy utilization during exercise (Bahr et al., 1991). Most of the weight loss is from fat, which has been further demonstrated by the triglyceride emptying of abdominal and gluteal adipocytes obtained both pre- and posttraining by biopsy (Rognum et al., 1982). The effects of increased energy intake were examined with the addition of 6,400 kcal/d over the 1,500 kcal/d normally given to cadets. The high-energy group still lost body weight (o.6 kg) but substantially less than the control group, which was fed 1,500 kcal/d (3.6 kg). There were no differences in performance between the two groups when compared for time on a 1-km assault course (days 2, 3, and 4), with 20 kg of combat equipment on a 350-m assault course requiring balance and agility (day 5), or on marksmanship scores (days 3 and 4) (Rognum et al., 1986). Although there were no differences in physical or mental performance attributable to energy intake, by the fourth day of this course, observer evaluations of all cadets rated them as totally ineffective soldiers (Rognum et al., 1986). This conclusion was attributed to the effects of sleep deprivation. In other, more-controlled laboratory studies of short-term high-energy deficit, tests of power, such as the Wingate test, and tests of isometric strength, including grip strength, have usually not been affected (Consolazio et al., 1967; Henschel et al., 1954; Hickner et al., 1991). However, Henschel et al. (1954) noted a reduced capacity for anaerobic work during 4.5 days of starvation. This finding was based on a substantial increase in lactate levels following a 75-s anaerobic treadmill run and a decrease in calculated efficiency of ~8 percent (Henschel et al., 1954). These changes occurred without a decrement in maximal aerobic capacity. Bahr et al. (1991) have noted a 15 percent decrease in efficiency following the 5-d Norwegian ranger course, measured at a fixed work load involving 30 minutes of treadmill at 50 percent of maximal oxygen uptake. In both of these short-term starvation studies, the decreased efficiency has been related to the increase in fat utilization. In both cases, the absence of food also produced severe gastric distress, presenting other potential complications to assessment of work performance (Henschel et al., 1954; Oektedalen et al., 1983).
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations Canadian Forces Commandos Study: Intensive Training With Small Energy Deficits Studies by Ira Jacobs involving Canadian Forces Commandos have examined the effects of supplemental carbohydrate feeding on physical performance and muscle glycogen levels during a 5-d high-intensity field training scenario (Jacobs et al., 1983, 1989). These studies include comparison between a group of soldiers receiving standard field rations (3,880 kcal/d offered; 3,350 kcal/d consumed) and a group receiving an additional energy supplement (5,420 kcal/d offered; 3,720 kcal/d consumed) to increase caloric intake above normal requirements to more closely match the requirements of this cold-weather exercise (5,500 to 6,500 kcal/d) (Jacobs et al., 1983). This situation reflects another form of "voluntary" underconsumption, where soldiers have difficulty ingesting enough energy to meet very high demands. In this study, a variety of strength parameters decreased from baseline levels, on the order of 15 percent, and aerobic capacity declined by 6 percent. These results should be interpreted as part of the "overtraining" phenomenon and may also include fatigue and motivation components in the posttesting. There were no differences between the two groups in terms of performance decrements or in muscle glycogen concentrations (Jacobs et al., 1989). Results of the study illustrate a problem for which a nutritional intervention has not yet been devised: the replenishment of muscle glycogen levels during a continuous effort without rest or with extraordinarily high daily energy expenditures (Costill et al., 1988). Endurance efforts such as the Tour de France may appear to be similar paradigms, but they differ because soldiers in these field exercises may not have rest periods greater than 2 hours at any given point, while cyclists usually have overnight rests. CONCLUSIONS The conclusions of Taylor et al. (1957) still ring true: It seems reasonable to conclude that a loss of about 10 percent of the body weight is an acceptable compromise in a survival situation when the intake of calories and salt are adequate to prevent extracellular dehydration and significant hypoglycemia(p. 429). They added that "it must be remembered that these results are limited to young men in good physical condition and that the rate of weight loss is important"(Taylor et al., 1957, p. 429). However, it appears that even a very high rate of weight loss for a short duration (< 1 week) probably has little effect on physical performance, as evidenced by the work of Consolazio, Johnson, and others. The primary concern during weight loss involves loss of muscle
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Not Eating Enough: Overcoming Underconsumption of Military Operational Rations strength, but this loss requires a substantial loss of muscle mass, occurring with body weight losses at least in excess of 5 percent and possibly 10 percent of initial body weight. Even a 15 percent decline in aerobic capacity has relatively little effect on soldier performance when it involves work at normal sustainable levels. As in the example of the field artillery men who adjusted their relative work load through increased efficiency, soldiers could readily accommodate a change of this magnitude. In the case of overnourished soldiers, some weight loss is likely to be beneficial to health and performance. Women have not been studied in the context of physical performance and weight loss in field conditions with operational rations. Such studies may provide a quite different relationship, since aerobic and upper body strength capacities are usually lower to begin with, and female soldiers are more prone to iron deficiency. However, female soldiers may perform better than men at low-intensity work during high-energy deficits because of their greater capacity for fat metabolism and larger fat stores. ACKNOWLEDGMENTS The author has relied heavily on reports about which John F. Patton and Herman Johnson had first-hand knowledge, and the author thanks them both for their assistance. The author also thanks Bradley Nindl for his help in fact checking and Lorraine Farinick for creating the figures. REFERENCES AR (Army Regulation) 40-25 1985. See U.S. Departments of the Army, the Navy, and the Air Force. Askew, E.W., J.R. Claybaugh, S.A. Cucinell, A.J. Young, and E.G. Szeto 1986. Nutrient intakes and work performance of soldiers during seven days of exercise at 7,200 feet 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.: Army Research Institute of Environmental Medicine. Bahr, R., P.K. Opstad, J.I. Medbo, and O.M. Sejersted 1991. Strenuous prolonged exercise elevates resting metabolic rate and causes reduced mechanical efficiency. Acta Physiol. Scand. 141:555–563.
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Representative terms from entire chapter: