Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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19 Maintenance of Body Weight at High Altitudes: In Search of 500 kcal/day
19 Maintenance of Body Weight at High Altitudes: In Search of 500 kcal/day
Pages 357-378
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From page 357... ...
National Academy Press 19 Maintenance of Body Weight at Altitude: In Search of 500 keel/day Gail E Butterfield' INTRODUCTION Weight loss while visiting at elevations not normally inhabited by the sojourner (at altitude)
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Starvation may be defined as a state where energy intake does not match energy need or as a state of negative energy balance. Ancel Keys in his seminal work on starvation in male conscientious objectors (Keys et al., 1950)
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Anorexia at Altitude: The Intake Side of Energy Balance Anorexia is defined as loss of appetite. As there is no direct measure of appetite, the question of anorexia at altitude has been approached primarily by monitoring food intake.
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. 1000 2000 3000 Sea Level Energy Intake (kcal/d)
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Weight maintenance was not accomplished in the Consolazio experiment, and the rate of weight loss after the first 2 days was similar to that seen in other studies where energy intake was not enforced (146 to 188 g/d; see Table 19-19. Other studies have attempted to maintain food intake by providing extremely palatable food.
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. The energy intake achieved, however, was sufficient to maintain performance parameters and lean body mass in these training troops, which suggests that the training had a protective effect on protein utilization- as has been shown previously at sea level (Todd et al., 1984~.
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In studies where food composition has been manipulated to enforce decreased carbohydrate intake at altitude, exercise performance has been adversely affected (Bigard et al., 1993~. Increased Energy Need: The Output Side of Energy Balance Basal Energy Needs Several reports in the literature suggest that BMR (the energy required to maintain body functions in the most minimal state)
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In contrast to previous reports where energy intake was reduced compared to sea level, Butterfield and co-workers (1992) found that when energy intakes were maintained at or above sea-level values throughout 3 weeks of exposure to altitude, BMR rose initially, then fell slightly, but remained elevated above sea-level values by 17 percent (see Figure 19-3~.
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. Interestingly, Butterfield and co-workers (Roberts et al., in press by, in a study subsequent to that mentioned above, matched energy intake with energy need (including increased basal needs)
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, with the conclusion that energy expended in activities of comparable intensity is constant throughout the range of altitudes where humans may be expected to work, and that this aspect of the energy balance equation does not increase energy needs at altitude. WEIGHT LOSS AT ALTITUDE Thus, as a consequence of decreased energy intake and increased basal energy needs, most individuals acutely exposed to high altitudes experience a significant negative energy balance and subsequent weight loss.
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Table 19-1 depicts data from studies that have provided adequate ctata to assess rate of weight loss. Although rates of weight loss range from 85 to 474 g/d, this table shows that the average rate of weight loss in ad libitum studies is about 200 g/d, or about 1.4 kg/wk, about three times greater than would be predicted from the potential negative energy balance estimated above.
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From page 369... ...
Subjects were in nitrogen balance during the sea-level control phase, which suggests that the energy intake provided during this time met energy needs (Calloway, 1975~. During the first week at altitude, when energy intake was equivalent to that at sea level (and thus slightly lower than need, not having been adjusted for increased BMR)
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A subsequent study by the same group suggests that both nitrogen balance and body weight can be maintained throughout a sojourn of 3 weeks at 4,300 m (14,110 ft) if aggressive attempts are made to cover increased energy needs by increased energy intake (Roberts et al., in press b)
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In the second study, energy intake was adjusted from day 1 of exposure, and weight loss was prevented in 9 of 11 subjects studied. As cats be seen Mom Figure 19-5, fluid losses in urine were significantly decreased under the circumstances of adequate energy intake, which suggests that at least some of the diuresis reported in the past may be a consequence of weight loss and may not be necessary under circumstances of hypoxia.
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First, the physiological response to hypoxia may be confused with the physiological response to negative energy balance, giving an incorrect picture as to the metabolic consequences of high-altitude exposure. This consequence is primarily a scientific one and may be acceptable.
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and consequences of weight loss at altitude, as well as provision of palatable rations and enforced food intake, may allow for a better matching of energy intake and energy requirement and may well be the difference between life and death for these individuals. AUTHOR'S CONCLUSIONS AND RECOMMENDATIONS Causes for Weight Loss at Altitude A variety of causes for weight loss at altitude have been previously delineated (Butterfield, 1990~.
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Under circumstances of adequate energy intake, physiological parameters measured at altitude, such as metabolic fuel source, will more adequately reflect the true response to hypoxia uncomplicated by negative energy balance. Weight loss at altitude is preventable and is unacceptable.
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b. Carbohydrate intake should supply around 60 percent of total energy intake to cover increased need for carbohydrate in the adequately fed individual.
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Reeves 1992 Increased energy intake minimizes weight loss in men at high altitude.
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Margen 1981 Estimate of energy requirements in young and elderly males confined to a metabolic unit.
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Deuster 1991 Consumption of a dehydrated ration for 31 days at moderate altitudes: Energy intakes and physical performance.
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