Energy expenditure climbing Mt. Everest KLAAS R. WESTERTERP, AND WIM H. M. SARIS
BENGT
KAYSER,
FRED
BROUNS,
JEAN
PIERRE
HERRY,
Department of Human Biology, University of Limburg, 6200 MD Maastricht, The Netherlands; Department of Physiology, University Medical Center, 1211 Geneva 4, Switxerlund; and Ecole Nationale de Ski et Alpinisme, 74403 Chamonix, France
comparable loss of 1.5 kg in four subjects moving from low altitude to 4,800 m and of 3.4 kg over a subsequent interval of 8 days climbing to 7,102 m. Subjects initially lost fat-free mass (FFM), and the further weight loss was mainly FM without overall changes in FFM. Both studies were performed in the field. Changes in anthropometry were monitored by measuring body weight, skinfold thickness, and limb circumferences. These techniques must be used with caution when the effects of altitude exposure are studied (6). However, as with other techniques such as computerized tomography (CT) scan, cross-sectional area determination, and underwater weighing, Rose et al. (16) showed that chronic hypobaric hypoxia leads to important weight loss from both FM and FFM. Those authors simulated a climb of Mt. Everest over 40 days in a decompression chamber, thus isolating the effect of hypoxia by excluding field factors like low ambient temperatures and dry air. The subjects had a mean weight loss of 7.4 kg, of which two-thirds was from FFM. This higher loss, compared with the field studies described above, was partly explained by the fact that the subjects’ daily exercise level decreased importantly with altitude exposure, leading to detraining. In the latter study, subjects had ad libitum access to a varietY of foods, because one objective was to study whether body weight could be maintained by offering palatable foods. As in other studies, energy intake (EI) decreased by 30-50% compared with sea level. The decrease of energy intake could not fully explain the weight loss. Rose et al. (16) calculated an expected weight loss of 1.7 kg on the basis of measured EI and estimated energy expenditure from predicted resting metabolic rate, adding energy for sedentary activities and exercise periods. These rehigh altitude; energy intake; body composition; doubly labeled sults suggest an increase in the rate of energy expendiwater ture at higher altitude, notwithstanding a negative energy balance that is usually accompanied by a reduction of energy expenditure. IT SEEMSTO BE DIFFICULT, if not impossible, to maintain We can currently measure energy expenditure under energy balance >4,500 m, and the ensuing weight loss is a free-living conditions by use of the doubly labeled water well-known phenomenon to high-altitude climbers. Until method (15). We therefore studied energy metabolism in now there has been no clear evidence whether the nega- climbers at high altitude, measuring simultaneously EI, tive energy balance is a result mainly of a lowered energy energy expenditure, and changes in body composition to intake or of an increased energy expenditure as well. gain insight into the changes in energy balance during Boyer and Blume (1) observed a mean weight loss of 1.9 kg in 13 subjects over 25 days moving from 600 to 5,400 m climbing at high altitude. and of 4.0 kg over a subsequent stay of 22 days at 5,4006,300 m or higher. The initial weight loss was mainly fat METHODS mass (FM), and the further weight loss was due mainly to Subjects were two women and three men, aged 36 t 4 muscle wasting. Guilland and Klepping (9) observed a (SD) yr and with a body mass index of 21.2 t 2.2 kg/m2, WESTERTERP,KLAAS R., BENGT KAYSER,FRED BROUNS, JEAN PIERREHERRY,ANDWIM H. M. SARIS.Energy expenditure climbing Mt. Euerest. J. Appl. Physiol. ‘73(5): l&5-1819, 1992.-Weight lossis a well-known phenomenon at high altitude. It is not clear whether the negative energy balance is due to an.orexia only or an increased energy expenditure as well. The objective of this study was to gain insight into this matter by measuring simultaneously energy intake, energy expenditure, and body composition during an expedition to Mt. Everest. Subjectswere two womenand three men between31 and 42 yr of age. Two subjects were observed during preparation at high altitude, including a 4-day stay in the Alps (4,260m), and subsequentlyduring four daytime stays in a hypobaric chamber (5,600-7,000m). Observations at high altitude on Mt. Everest covered a 7- to lo-day interval just before the summit was reachedin three subjectsand included the summit (8,872m) in a fourth. Energy intake (EI) was measuredwith a dietary record, averagedaily metabolic rate (ADMR) with doubly labeled water, and resting metabolic rate (RMR) with respiratory gas analysis. Body compositionwas measuredbefore and after the interval from body mass,skinfold thickness, and total body water. Subjects were in negative energy balance (-5.7 t I.9 MJ/day) in both situations, during the preparation in the Alps and on Mt. Everest. The lossof fat massover the observation intervals was 1.4 2 0.7 kg, on averagetwo-thirds of the weight loss (2.2 t 1.5 kg), and was significantly correlated with the energy deficit (r = 0.84,P < 0.05). EI on Mt. Everest was9-13% lower than during the preparation in the Alps. ADMR wasat a high level (13.6 t 1.7 MJ/day). The activity level, expressedas ADMR/RMR, was2.2 ,t 0.3 and 2.2 t 0.1, on the basisof measured and predicted RMR values, respectively. The results from this study illustrate the problems of maintaining energy balance while climbing at high altitude. EI is low, whereasenergy expenditure reaches values comparableto those of highly trained endurance athletes at sealevel.
0161-7567/92 $2.00 Copyright 0 1992 the American Physiological Society
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z ‘Ooo z ;
6000
5000
I I
I
I
1
I
I
I
I
0
5
10
15
20
25
30
35
time
(days)
FIG. 1. Altitude profile of sdjs 1 and 2 during expedition on Mt. Everest. Circles, start and end of observation interval. See Table 1 for additional details.
all members of an expedition to reach the summit of Mt. Everest. Two subjects were observed during preparation for the expedition, including a 4-day stay in a field laboratory on Mont Blanc in the French Alps (observatoire Vallot, 4,260 m), with daily climbing activities between 3,500 and 4,800 m, and subsequently four daytime stays in a hypobaric chamber, simulating ascents to 5,6007,000 m on Mt. Everest. All subjects were observed during the first summit attempt on Mt. Everest, climbing between 5,300 and 8,872 m, The average duration of the observation interval on Mt. Everest was 8 t 1 days. Three subjects reached the summit (8,872 m) within 3 days a.fter the observation interval; in one subject the ascent to the summit was included in the observation interval (Fig. 1). Measurements of energy metabolism comprised EI and water intake, energy expenditure, water loss, and changes in body composition over the observation interval. EI was measured with a dietary record. Subjects recorded their food and fluid intake in . a di .ary in ho usehold measures, including brand names and cooki .w recipes where appropriate and weights of items as well. After the expedition, a trained nutritionist examined the diary to clarify the records and eliminate inconsistencies with the subject. The energy content of the food intake was then derived from food tables, and the percentage (en %) for the intake of carbohydrate, fat, and protein was calculated. Energy expenditure was measured under both resting postabsorptive conditions [resting metabolic rate (RMR)] and field conditions [average daily metabolic rate (ADMR)]. RMR was measured in the morning immediately after subjects woke. They remained in bed and, wearing a noseclip, breathed for 15 min through a mouthpiece. In the Alps just before the observation period and on Mt. Everest immediately afterward, the first 5 min were used for adaptation; the subsequent 109min interval was used for respiratory gas analysis. In the Alps a metabolic cart (Oxycon 4, Mijnhardt) was used,
MT. EVEREST
whereas on Mt. Everest conventional Douglas bags, a Singer dry gas meter, and gas analyzers (Oxynos 1-C and LB-2, for 0, and CO,, respectively, Leybold Haereus) were used. Both the metabolic cart and the gas analyzers had previously been calibrated with gas mixtures of known composition. Energy expenditure was calculated from respiratory gas exchange with the Weir formula (20). Alternatively, RMR was calculated from subject characteristics with the equation from Harris and Benedict (10). ADMR was measured with doubly labeled water. Subjects were given a weighed dose of a mixture of 99.84 at% 2H20 in 10.05 at% H2180, such that baseline levels were increased with 2150 ppm for 2H and 2300 ppm for l&O. Urine samples for isotope measurement were collected before dosing at night and from the second voiding every morning afterward until the end of the observation interval, Urine was collected in dry 50-ml vials, which were sealed to prevent evaporative fractionation. After descent, the vials were shaken, and duplicate 2-ml samples were stored in glass containers until analysis. Isotope abundances in the urine samples were measured with an isotope ratio mass spectrometer (VG Isogas, Aqua Sira), and CO, production was calculated as previously described (21, 24). Total body water calculated from the isotope dilution spaces at the start of the observation interval was corrected for the change over the observation intervals. The latter correction was calculated from the difference between initial and final body weight, with the assumption that the change of the body water volume was linear and proportional to the change in weight. All samples were measured in duplicate. Differences between duplicates were always -cl ppm. CO, production was converted to ADMR by use of an energy equivalent of 531 kJ/mol [respiratory quotient (RQ) = 0.851, according to the average metabolic fuel quotient calculated from the macronutrient composition of the diet as measured with the dietary records and the use of body energy reserves. In both situations, the Alps and Mt. Everest, respectively, two and three other participants of the team collected urine samples over the same intervals without getting an isotope dose to allow for corrections due to changes in the baseline abundances. Water loss was calculated from the deuterium elimination rate as measured with the doubly labeled water method (15). Results were corrected for fractionation with &. 2 of Fjeld et al. (5). The water loss from the lungs subject to fractionation was calculated using the formula proposed by Ferrus et al. (4), with the assumption of a mean ventilatory frequency of 30fmin, a mean ambient temperature of O”C, a barometric pressure of 380 Torr, and a partial water vapor pressure of 0 Torr. The insensible cutaneous water loss was assumed to be 0.07 g min-l mm2 (5) on the basis of nearly full and permanent clothing. Body composition was calculated from body mass and skinfold thicknesses measured at the start and the end of the observation interval of EI and ADMR. Body mass was measured on rising, after emptying of the bladder, on a previously calibrated household scale (Soenhle) to the nearest 0.5 kg. Percent body fat was calculated from skinfold thickness, summing the biceps, triceps, supraill
l
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TABLE 1. Total body water, fractional elimination rates from body water of excess180 and 2H, fluid intake, fluid output, energy intake, and average daily metabolic rate Subj No.
TBW, liters
k 18, day-l
1 2 Mean t SD
29.0 40.4 34.7t8.1
0.11817 0.14479t0.03764
0.13648 0.08412 0.11030t0.03702
1
28.5 39.9 30.8 41.8 32.7 34.7k5.8
0.16794 0.09403 0.12781 0.12560 0.13683 0.13044t0.02647
0.13202 0.06449 0.09594 0.09517 0.10327 0.09818t0.02408
k2, day-’
Fluid,, I/day
FluiLt l/day
EI, MJ/day
ADMR, MJ/day
2.9 2.7 2.8tO.l
3.9 3.4 3.7t0.4
9.4 10.7 10.1+,0.9
12.1 17.2 14.7t3.6
2.7 2.2 1.8 2.4 2.0 2.220.3
3.8 2.5 2.9 4.0 3.4 3.3t0.6
8.2 9.7 5.8 7.0 6.9 7.5H.5
12.3 14.9 11.7 15.6 13.5 13.6t1.7
t
Alps 0.17140
Mt.
2 3 4 5 Mean t SD
Everest
TBW, mean total body water as calculated from initial isotope dilution space and body mass change; jz18and b, fractional elimination rates from body water of excess la0 and 2H, respectively; Flu&, fluid intake; Fluiku,, fluid output; EI, energy intake; ADMR, average daily metabolic rate.
iac, and subscapular sites and using the tables from Durnin and Womersley (2). Alternatively, total body water was measured by 2H and 180 dilution, as included in the doubly labeled water, at the start of the observation interval. FFM was calculated from total body water, assuming a hydration factor of 0.73. To obtain additional information about changes in body composition, lower limb volume and its partition between FM and FFM were calculated according to Jones and Pearson (12), with use of limb circumferences measured with a tape and skinfolds measured with a caliper at the start and the end of the observation interval. It is difficult to perform energy balance studies under field conditions at sea level. Living in camps at high altitude further complicates the measurements. To minimize bias due to experimental conditions, the protocol of the study was such that B. Kayser and K. R. Westerterp joined the preparation expedition in the Alps, whereas B. Kayser instructed the subjects during the Everest expedition, being near the base camp to do the RMR measurements and to collect the samples and the activity and food records. One of the subjects (CJ), a trained physician, was instructed to look after the measurement procedures during the climbing activities, including isotope dosing, urine sampling, and anthropometry. Results are presented as means t SD unless stated differently. Values obtained at the beginning and the end of the observation interval on Mt. Everest were compared with Student’s t test for paired observations. RESULTS
The composition of the diet was 53 t 3 en% carbohydrate, 13 t 2 en% protein, and 34 t 2 en% fat, very close to the present day nutritional advice of 55 en% carbohydrate, lo-15 en% protein, and 30-35 en% fat. EIs of the two subjects during the preparation in the Alps were 9.4 and 10.7 mg/day, respectively, 13% higher than on Mt. Everest (Table 1). In all subjects there was a tendency for EI to decrease during the observation intervals while the nutrient composition remained the same. Fluid intake tended to be lower on Mt. Everest than during the preparation in the Alps. There was a mean difference of 15 ppm for 180 and 10
ppm for 2H between background levels in the Alps, where subjects drank lowland water, and on Mt. Everest, where all water for consumption was produced by melting snow. However, the background isotope levels in the five members of the team not receiving labeled water did not show any systematic changes during the observation interval, with allowance for calculation of water loss and ADMR from isotope elimination without corrections for a changing baseline. Water loss and energy expenditure as calculated from isotope elimination rates are presented in Table 1. Comparing water loss with water intake needs correction of intake for metabolic water (see DISCUSSION). ADMR was higher than EI in all subjects and in both situations; the mean difference was 39 t 11% of ADMR. RMR showed individual differences of l-22% between measured and calculated values. The differences were not systematic, i.e., in four of seven cases the calculated value was lower, in one case there was no difference, and in the remaining two cases the predicted value was higher. Calculating the activity level of the subjects from the quotient ADMR/RMR yielded 2.3 t 0.3 (range 2.0-2.7) on the basis of measured RMR values and 2.2 t 0.1 (range 2.1-2.4) on the basis of calculated RMR values. Energy expenditure during the preparation in the Alps was similar to that during the expedition to Mt. Everest (Table 1). All subjects (except one in the Alps) lost weight. The value of FM change in one subject on Mt. Everest was not reliable, because she was the only person present in the camp at the start of the observation interval with experience in measuring skinfold thicknesses; it was therefore omitted. The changes in FM and FFM of the remaining observations were 1.4 t 0.7 and -0.8 t 1.4 kg, respectively. Subjects lost body fat in both situations, despite one subject’s gain of 0.6 kg body mass in the Alps. Lower limb anthropometry revealed a significant loss of lean mass on Mt. Everest from 6.37 to 6.01 liters (-6%). When EI and ADMR were compared, all subjects were in negative energy balance in the Alps (-4.6 t 2.7 MJ/day) and on Mt. Everest (-5.8 t 1.8 MJ/day). Differences between EI and ADMR ranged between 2.2 and 8.6 MJ/ day. There was a significant relation between the energy deficit and the change in FM (AFM)
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AFM = O.O46(EI - ADMR)
+ O.O97(r = 0.86, P < 0.05)
where AFM is in kilograms are in megajoules per day.
per day and EI and ADMR
DISCUSSION
As expected, the subjects lost weight during the observation period on Mt. Everest. The weight loss amounted to an average of 4% of the starting weight and was partitioned into two-thirds FM and one-third FFM. These amounts may be somewhat inaccurate because of losses of body water that may occur at high altitude (6). On the other hand, values are not different from changes in body composition observed in studies with an energy-restricted diet (23) and other studies at high altitude (1, 16). The loss of FFM, a phenomenon that can become more prominent when the .exposure to high altitude is observed for a longer time (1,3), is also illustrated by the loss of 6% of lower limb lean mass. In fact, losses up to 17% of thigh cross-sectional area calculated from CT scans have been reported (3, 16). EI at high altitude was low, especially on Mt. Everest, as has been reported (9). We did not perform low-altitude measurements in the same subjects, but the decrease of EI in the two subjects between the Alps and the higher Everest situation is indicative. EI was lower than in a comparable group of sedentary subjects at sea level, measured with the same method (22). Of course there is a tendency for underreporting with self-report (19, 26). The values on EI in this study were not so susceptible to underreporting, because the subjects were closely supervised in the Alps, and on Mt. Everest all the food was carried by the subjects themselves, giving them optimal opportunity to keep track of their intake. In addition, supervision on Mt. Everest by the climbing physician (CJ) and daily radio contact with the base camp when the subjects were on the mountain optimized diary entries. Energy expenditure has not yet been measured with doubly labeled water at extreme altitude. The first study under altitude conditions is a recent comparison of doubly labeled water with intake balance during strenuous exercise at 2,200-2,550 m, which shows acceptable agreement if corrections are made for changes in baseline isotopic abundances (11). Baseline isotope levels in the Alps were close to sea level values, because subjects drank lowland water. On Mt. Everest, baseline isotope levels were markedly decreased compared with the values from the Alps, probably because of the use of water from melted snow. However, the levels did not decrease over time in the control subjects; the new baseline apparently had stabilized before the subjects were dosed, allowing the calculation of ADMR without corrections for a changing baseline. Another potential source of error in calculations of CO, production from isotope turnover is physical fractionation. Breath water vapor and insensible cutaneous water loss are isotopically fractionated. We used the appropriate correction factors to overcome these errors under lowland conditions. Breath water vapor loss is higher at high altitude than at sea level because of a higher ventilation rate, and lower water vapor partial pressure and temperature of the inspired air. When the amount of CO, produced was used, the mean breath
CLIMBING
MT.
EVEREST
water loss at altitude was 660 ml/day, estimated from the formula from Ferrus et al. (4). On the other hand, insensible cutaneous water loss, estimated at 170 ml/day (5), was lower because of nearly full and permanent clothing, adapted to the environmental conditions. Thus the rate of isotopically fractionated water loss was comparable to lowland conditions. The calculated water loss of the subjects was 2.5-3.9 l/day, only slightly higher than at sea level. Water intake, ranging from 1.8 to 2.9 l/day, did not cover water loss. However, metabolic water production was high. At the measured high levels of energy expenditure, calculated metabolic water production was 0.5 l/day. In addition, humans at high altitude typically lose body mass and body water. Thus there was no systematic discrepancy between reported water intake and calculated water needs. Converting CO, production to energy expenditure, we used the energy equivalent of CO, for an average diet with 40 en% fat, lo-15 en% protein, and 45-50 en% carbohydrate. Although the subjects consumed a low-fat diet, their actual energy-substrate utilization was higher in fat and protein because of the mobilization of body stores. There are indications that RMR may be higher after a change from low to high altitude (7, 8, 18). However, measured RMR at altitude was not systematically different from predicted values for sea-level conditions. Roza and Shizgal (17) estimate the precision of the Harris Benedict equation for predicting RMR to be 14%. The change in RMR after a change from low to high altitude is likely to be smaller. The activity level of the subjects, as reflected in ADMR-to-RMR ratios, was surprisingly high. ADMR/ RMR values normally range between 1.5 and 1.8 for light to moderately active subjects (27). In the present study, ADMR/RMR was higher in all subjects and comparable to the value observed in highly active subjects at sea level engaged in endurance exercise like long-distance running (22). At sea level, sustained metabolic scope in mammals, defined as the maximal energy expenditure that can be sustained indefinitely, ranges from 1.5 to 5.0, depending on the characteristics of the animal (14). In humans, values up to 5.0 have been reported in highly trained cyclists participating in the Tour de France (25) and seem to be the maximum attainable for humans in sea-level conditions. At altitude, the decrease in barometric pressure severely limits the availability of 0, and, as a consequence, maximum 0, uptake (VO,,,) decreases as a function of altitude. This probably limits the sustained metabolic scope attainable at altitude. Using measured EI, RMR, ADMR, and the activity diaries, we could estimate energy expenditure during climbing activities by calculating ADMR minus resting energy expenditure [calculated by adding 20% of basal metabolic rate (BMR) during daytime for arousal, dietinduced thermogenesis, and sedentary activity]. Thus climbing resulted in an extra energy expenditure of 6.6 MJ/day. The average time spent climbing on Mt. Everest was 3.5 h/day. If these two numbers are combined and an energy equivalent of 20 kJ/l 0, is used, the 0, consumption during climbing could then have been 29.6
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ENERGY
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ml 1 min-l . kg-‘. This would be at vo 2maxas measured in elite climbers
50-60% of sea-level (13). Such a level is probably near the maximum aerobic capacity at those altitudes and is compatible with the subjects’ sense of intensive exertion while climbing Mt. Everest. On the whole, it seems likely that the sustained metabolic scope at altitude is lower than at sea level. It is noteworthy that subject 5, whose ascent to the summit was included in the observation interval and who had already climbed Mt. Everest twice without supplementary O,, reached the highest VO, (33.6 ml min-’ kg-l). The discrepancy between EI and ADMR was related to the loss of FM. The mean energy equivalent of weight loss was 31 MJ/kg, within the range of 28-32 MJ/kg for two-thirds fat and the remainder only water or only protein, respectively. Thus the energy balance equation fits: EI = EE - ABM. In cone lusion, the results from this study show the prob lems of the maintenance of energy balan .ce du ring high-altitude climbing. EI is low, whereas energy expenditure is equivalent to values that are found only in endurance athletes at sea level.
CLIMBING
l
l
l
We thank the participants of the study: Christine Janin, Pascal Tournere, Marie Guilaine Jesenne, Erik Decamp, and Marc Battard; Dr. Christine Janin, who supervised the measurements during climbing; Loek Wouters, who did the isotopic analysis of the samples; and Nicole Duysens, who analyzed the food records. The cost of the doubly labeled water was covered by an Isostar Research Grant from Sandoz Nutrition, Bern, Switzerland. Federation Francaise pour la Montagne et 1’Escalade partly funded the observations in the Alps, and we were given permission to use the Italian Research Laboratory near basecamp during the Mt. Everest expedition. Address for reprint requests: K. R. Westerterp, Dept. of Human Biology, University of Limburg, PO Box 616,620O MD Maastricht, The Netherlands. Received 4 September 1991; accepted in final form 5 June 1992. REFERENCES S. J., AND F. D. BLUME. Weight loss and changes in body composition at high altitude. J. Appl. Physiol. 57: 1580-1585,1984. 2. DURNIN, J. V. G. A., AND J. WOMERSLEY. Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years. Br. J. 1. BOYER,
Nutr. 32: 77-97, 1974. 3. FERRETTI, G., H. HAUSER,
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K. R., W. H. M. SARIS, M. VAN Es, AND F. TEN the doubly labeled water technique in humans during heavy sustained exercise. J. Appl. Physiol. 61: 2162-2167,1986. 26. WESTERTERP, K. R., W. P. H. G. VERBOEKET-VAN DE VENNE, G. A. L. MEIJER, AND F. TEN HOOR. Self-reported intake as a measure for energy intake: a validation against doubly labelled water. In: Obesity in Europe, edited by G. Ailhaud, B. Guy-Grand, M. Lafontan, and D. Ricquier. London: Libbey, 1992, p. 17-22. 27. WORLD HEALTH ORGANIZATION. Energy and ments: Report of a Joint FAOIWHOKJNU Expert
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BENGT
KAYSER,
FRED
BROUNS,
JEAN
PIERRE
HERRY,
Department of Human Biology, University of Limburg, 6200 MD Maastricht, The Netherlands; Department of Physiology, University Medical Center, 1211 Geneva 4, Switxerlund; and Ecole Nationale de Ski et Alpinisme, 74403 Chamonix, France
comparable loss of 1.5 kg in four subjects moving from low altitude to 4,800 m and of 3.4 kg over a subsequent interval of 8 days climbing to 7,102 m. Subjects initially lost fat-free mass (FFM), and the further weight loss was mainly FM without overall changes in FFM. Both studies were performed in the field. Changes in anthropometry were monitored by measuring body weight, skinfold thickness, and limb circumferences. These techniques must be used with caution when the effects of altitude exposure are studied (6). However, as with other techniques such as computerized tomography (CT) scan, cross-sectional area determination, and underwater weighing, Rose et al. (16) showed that chronic hypobaric hypoxia leads to important weight loss from both FM and FFM. Those authors simulated a climb of Mt. Everest over 40 days in a decompression chamber, thus isolating the effect of hypoxia by excluding field factors like low ambient temperatures and dry air. The subjects had a mean weight loss of 7.4 kg, of which two-thirds was from FFM. This higher loss, compared with the field studies described above, was partly explained by the fact that the subjects’ daily exercise level decreased importantly with altitude exposure, leading to detraining. In the latter study, subjects had ad libitum access to a varietY of foods, because one objective was to study whether body weight could be maintained by offering palatable foods. As in other studies, energy intake (EI) decreased by 30-50% compared with sea level. The decrease of energy intake could not fully explain the weight loss. Rose et al. (16) calculated an expected weight loss of 1.7 kg on the basis of measured EI and estimated energy expenditure from predicted resting metabolic rate, adding energy for sedentary activities and exercise periods. These rehigh altitude; energy intake; body composition; doubly labeled sults suggest an increase in the rate of energy expendiwater ture at higher altitude, notwithstanding a negative energy balance that is usually accompanied by a reduction of energy expenditure. IT SEEMSTO BE DIFFICULT, if not impossible, to maintain We can currently measure energy expenditure under energy balance >4,500 m, and the ensuing weight loss is a free-living conditions by use of the doubly labeled water well-known phenomenon to high-altitude climbers. Until method (15). We therefore studied energy metabolism in now there has been no clear evidence whether the nega- climbers at high altitude, measuring simultaneously EI, tive energy balance is a result mainly of a lowered energy energy expenditure, and changes in body composition to intake or of an increased energy expenditure as well. gain insight into the changes in energy balance during Boyer and Blume (1) observed a mean weight loss of 1.9 kg in 13 subjects over 25 days moving from 600 to 5,400 m climbing at high altitude. and of 4.0 kg over a subsequent stay of 22 days at 5,4006,300 m or higher. The initial weight loss was mainly fat METHODS mass (FM), and the further weight loss was due mainly to Subjects were two women and three men, aged 36 t 4 muscle wasting. Guilland and Klepping (9) observed a (SD) yr and with a body mass index of 21.2 t 2.2 kg/m2, WESTERTERP,KLAAS R., BENGT KAYSER,FRED BROUNS, JEAN PIERREHERRY,ANDWIM H. M. SARIS.Energy expenditure climbing Mt. Euerest. J. Appl. Physiol. ‘73(5): l&5-1819, 1992.-Weight lossis a well-known phenomenon at high altitude. It is not clear whether the negative energy balance is due to an.orexia only or an increased energy expenditure as well. The objective of this study was to gain insight into this matter by measuring simultaneously energy intake, energy expenditure, and body composition during an expedition to Mt. Everest. Subjectswere two womenand three men between31 and 42 yr of age. Two subjects were observed during preparation at high altitude, including a 4-day stay in the Alps (4,260m), and subsequentlyduring four daytime stays in a hypobaric chamber (5,600-7,000m). Observations at high altitude on Mt. Everest covered a 7- to lo-day interval just before the summit was reachedin three subjectsand included the summit (8,872m) in a fourth. Energy intake (EI) was measuredwith a dietary record, averagedaily metabolic rate (ADMR) with doubly labeled water, and resting metabolic rate (RMR) with respiratory gas analysis. Body compositionwas measuredbefore and after the interval from body mass,skinfold thickness, and total body water. Subjects were in negative energy balance (-5.7 t I.9 MJ/day) in both situations, during the preparation in the Alps and on Mt. Everest. The lossof fat massover the observation intervals was 1.4 2 0.7 kg, on averagetwo-thirds of the weight loss (2.2 t 1.5 kg), and was significantly correlated with the energy deficit (r = 0.84,P < 0.05). EI on Mt. Everest was9-13% lower than during the preparation in the Alps. ADMR wasat a high level (13.6 t 1.7 MJ/day). The activity level, expressedas ADMR/RMR, was2.2 ,t 0.3 and 2.2 t 0.1, on the basisof measured and predicted RMR values, respectively. The results from this study illustrate the problems of maintaining energy balance while climbing at high altitude. EI is low, whereasenergy expenditure reaches values comparableto those of highly trained endurance athletes at sealevel.
0161-7567/92 $2.00 Copyright 0 1992 the American Physiological Society
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ENERGY
EXPENDITURE
CLIMBING
z ‘Ooo z ;
6000
5000
I I
I
I
1
I
I
I
I
0
5
10
15
20
25
30
35
time
(days)
FIG. 1. Altitude profile of sdjs 1 and 2 during expedition on Mt. Everest. Circles, start and end of observation interval. See Table 1 for additional details.
all members of an expedition to reach the summit of Mt. Everest. Two subjects were observed during preparation for the expedition, including a 4-day stay in a field laboratory on Mont Blanc in the French Alps (observatoire Vallot, 4,260 m), with daily climbing activities between 3,500 and 4,800 m, and subsequently four daytime stays in a hypobaric chamber, simulating ascents to 5,6007,000 m on Mt. Everest. All subjects were observed during the first summit attempt on Mt. Everest, climbing between 5,300 and 8,872 m, The average duration of the observation interval on Mt. Everest was 8 t 1 days. Three subjects reached the summit (8,872 m) within 3 days a.fter the observation interval; in one subject the ascent to the summit was included in the observation interval (Fig. 1). Measurements of energy metabolism comprised EI and water intake, energy expenditure, water loss, and changes in body composition over the observation interval. EI was measured with a dietary record. Subjects recorded their food and fluid intake in . a di .ary in ho usehold measures, including brand names and cooki .w recipes where appropriate and weights of items as well. After the expedition, a trained nutritionist examined the diary to clarify the records and eliminate inconsistencies with the subject. The energy content of the food intake was then derived from food tables, and the percentage (en %) for the intake of carbohydrate, fat, and protein was calculated. Energy expenditure was measured under both resting postabsorptive conditions [resting metabolic rate (RMR)] and field conditions [average daily metabolic rate (ADMR)]. RMR was measured in the morning immediately after subjects woke. They remained in bed and, wearing a noseclip, breathed for 15 min through a mouthpiece. In the Alps just before the observation period and on Mt. Everest immediately afterward, the first 5 min were used for adaptation; the subsequent 109min interval was used for respiratory gas analysis. In the Alps a metabolic cart (Oxycon 4, Mijnhardt) was used,
MT. EVEREST
whereas on Mt. Everest conventional Douglas bags, a Singer dry gas meter, and gas analyzers (Oxynos 1-C and LB-2, for 0, and CO,, respectively, Leybold Haereus) were used. Both the metabolic cart and the gas analyzers had previously been calibrated with gas mixtures of known composition. Energy expenditure was calculated from respiratory gas exchange with the Weir formula (20). Alternatively, RMR was calculated from subject characteristics with the equation from Harris and Benedict (10). ADMR was measured with doubly labeled water. Subjects were given a weighed dose of a mixture of 99.84 at% 2H20 in 10.05 at% H2180, such that baseline levels were increased with 2150 ppm for 2H and 2300 ppm for l&O. Urine samples for isotope measurement were collected before dosing at night and from the second voiding every morning afterward until the end of the observation interval, Urine was collected in dry 50-ml vials, which were sealed to prevent evaporative fractionation. After descent, the vials were shaken, and duplicate 2-ml samples were stored in glass containers until analysis. Isotope abundances in the urine samples were measured with an isotope ratio mass spectrometer (VG Isogas, Aqua Sira), and CO, production was calculated as previously described (21, 24). Total body water calculated from the isotope dilution spaces at the start of the observation interval was corrected for the change over the observation intervals. The latter correction was calculated from the difference between initial and final body weight, with the assumption that the change of the body water volume was linear and proportional to the change in weight. All samples were measured in duplicate. Differences between duplicates were always -cl ppm. CO, production was converted to ADMR by use of an energy equivalent of 531 kJ/mol [respiratory quotient (RQ) = 0.851, according to the average metabolic fuel quotient calculated from the macronutrient composition of the diet as measured with the dietary records and the use of body energy reserves. In both situations, the Alps and Mt. Everest, respectively, two and three other participants of the team collected urine samples over the same intervals without getting an isotope dose to allow for corrections due to changes in the baseline abundances. Water loss was calculated from the deuterium elimination rate as measured with the doubly labeled water method (15). Results were corrected for fractionation with &. 2 of Fjeld et al. (5). The water loss from the lungs subject to fractionation was calculated using the formula proposed by Ferrus et al. (4), with the assumption of a mean ventilatory frequency of 30fmin, a mean ambient temperature of O”C, a barometric pressure of 380 Torr, and a partial water vapor pressure of 0 Torr. The insensible cutaneous water loss was assumed to be 0.07 g min-l mm2 (5) on the basis of nearly full and permanent clothing. Body composition was calculated from body mass and skinfold thicknesses measured at the start and the end of the observation interval of EI and ADMR. Body mass was measured on rising, after emptying of the bladder, on a previously calibrated household scale (Soenhle) to the nearest 0.5 kg. Percent body fat was calculated from skinfold thickness, summing the biceps, triceps, supraill
l
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ENERGY
EXPENDITURE
CLIMBING
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MT. EVEREST
TABLE 1. Total body water, fractional elimination rates from body water of excess180 and 2H, fluid intake, fluid output, energy intake, and average daily metabolic rate Subj No.
TBW, liters
k 18, day-l
1 2 Mean t SD
29.0 40.4 34.7t8.1
0.11817 0.14479t0.03764
0.13648 0.08412 0.11030t0.03702
1
28.5 39.9 30.8 41.8 32.7 34.7k5.8
0.16794 0.09403 0.12781 0.12560 0.13683 0.13044t0.02647
0.13202 0.06449 0.09594 0.09517 0.10327 0.09818t0.02408
k2, day-’
Fluid,, I/day
FluiLt l/day
EI, MJ/day
ADMR, MJ/day
2.9 2.7 2.8tO.l
3.9 3.4 3.7t0.4
9.4 10.7 10.1+,0.9
12.1 17.2 14.7t3.6
2.7 2.2 1.8 2.4 2.0 2.220.3
3.8 2.5 2.9 4.0 3.4 3.3t0.6
8.2 9.7 5.8 7.0 6.9 7.5H.5
12.3 14.9 11.7 15.6 13.5 13.6t1.7
t
Alps 0.17140
Mt.
2 3 4 5 Mean t SD
Everest
TBW, mean total body water as calculated from initial isotope dilution space and body mass change; jz18and b, fractional elimination rates from body water of excess la0 and 2H, respectively; Flu&, fluid intake; Fluiku,, fluid output; EI, energy intake; ADMR, average daily metabolic rate.
iac, and subscapular sites and using the tables from Durnin and Womersley (2). Alternatively, total body water was measured by 2H and 180 dilution, as included in the doubly labeled water, at the start of the observation interval. FFM was calculated from total body water, assuming a hydration factor of 0.73. To obtain additional information about changes in body composition, lower limb volume and its partition between FM and FFM were calculated according to Jones and Pearson (12), with use of limb circumferences measured with a tape and skinfolds measured with a caliper at the start and the end of the observation interval. It is difficult to perform energy balance studies under field conditions at sea level. Living in camps at high altitude further complicates the measurements. To minimize bias due to experimental conditions, the protocol of the study was such that B. Kayser and K. R. Westerterp joined the preparation expedition in the Alps, whereas B. Kayser instructed the subjects during the Everest expedition, being near the base camp to do the RMR measurements and to collect the samples and the activity and food records. One of the subjects (CJ), a trained physician, was instructed to look after the measurement procedures during the climbing activities, including isotope dosing, urine sampling, and anthropometry. Results are presented as means t SD unless stated differently. Values obtained at the beginning and the end of the observation interval on Mt. Everest were compared with Student’s t test for paired observations. RESULTS
The composition of the diet was 53 t 3 en% carbohydrate, 13 t 2 en% protein, and 34 t 2 en% fat, very close to the present day nutritional advice of 55 en% carbohydrate, lo-15 en% protein, and 30-35 en% fat. EIs of the two subjects during the preparation in the Alps were 9.4 and 10.7 mg/day, respectively, 13% higher than on Mt. Everest (Table 1). In all subjects there was a tendency for EI to decrease during the observation intervals while the nutrient composition remained the same. Fluid intake tended to be lower on Mt. Everest than during the preparation in the Alps. There was a mean difference of 15 ppm for 180 and 10
ppm for 2H between background levels in the Alps, where subjects drank lowland water, and on Mt. Everest, where all water for consumption was produced by melting snow. However, the background isotope levels in the five members of the team not receiving labeled water did not show any systematic changes during the observation interval, with allowance for calculation of water loss and ADMR from isotope elimination without corrections for a changing baseline. Water loss and energy expenditure as calculated from isotope elimination rates are presented in Table 1. Comparing water loss with water intake needs correction of intake for metabolic water (see DISCUSSION). ADMR was higher than EI in all subjects and in both situations; the mean difference was 39 t 11% of ADMR. RMR showed individual differences of l-22% between measured and calculated values. The differences were not systematic, i.e., in four of seven cases the calculated value was lower, in one case there was no difference, and in the remaining two cases the predicted value was higher. Calculating the activity level of the subjects from the quotient ADMR/RMR yielded 2.3 t 0.3 (range 2.0-2.7) on the basis of measured RMR values and 2.2 t 0.1 (range 2.1-2.4) on the basis of calculated RMR values. Energy expenditure during the preparation in the Alps was similar to that during the expedition to Mt. Everest (Table 1). All subjects (except one in the Alps) lost weight. The value of FM change in one subject on Mt. Everest was not reliable, because she was the only person present in the camp at the start of the observation interval with experience in measuring skinfold thicknesses; it was therefore omitted. The changes in FM and FFM of the remaining observations were 1.4 t 0.7 and -0.8 t 1.4 kg, respectively. Subjects lost body fat in both situations, despite one subject’s gain of 0.6 kg body mass in the Alps. Lower limb anthropometry revealed a significant loss of lean mass on Mt. Everest from 6.37 to 6.01 liters (-6%). When EI and ADMR were compared, all subjects were in negative energy balance in the Alps (-4.6 t 2.7 MJ/day) and on Mt. Everest (-5.8 t 1.8 MJ/day). Differences between EI and ADMR ranged between 2.2 and 8.6 MJ/ day. There was a significant relation between the energy deficit and the change in FM (AFM)
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AFM = O.O46(EI - ADMR)
+ O.O97(r = 0.86, P < 0.05)
where AFM is in kilograms are in megajoules per day.
per day and EI and ADMR
DISCUSSION
As expected, the subjects lost weight during the observation period on Mt. Everest. The weight loss amounted to an average of 4% of the starting weight and was partitioned into two-thirds FM and one-third FFM. These amounts may be somewhat inaccurate because of losses of body water that may occur at high altitude (6). On the other hand, values are not different from changes in body composition observed in studies with an energy-restricted diet (23) and other studies at high altitude (1, 16). The loss of FFM, a phenomenon that can become more prominent when the .exposure to high altitude is observed for a longer time (1,3), is also illustrated by the loss of 6% of lower limb lean mass. In fact, losses up to 17% of thigh cross-sectional area calculated from CT scans have been reported (3, 16). EI at high altitude was low, especially on Mt. Everest, as has been reported (9). We did not perform low-altitude measurements in the same subjects, but the decrease of EI in the two subjects between the Alps and the higher Everest situation is indicative. EI was lower than in a comparable group of sedentary subjects at sea level, measured with the same method (22). Of course there is a tendency for underreporting with self-report (19, 26). The values on EI in this study were not so susceptible to underreporting, because the subjects were closely supervised in the Alps, and on Mt. Everest all the food was carried by the subjects themselves, giving them optimal opportunity to keep track of their intake. In addition, supervision on Mt. Everest by the climbing physician (CJ) and daily radio contact with the base camp when the subjects were on the mountain optimized diary entries. Energy expenditure has not yet been measured with doubly labeled water at extreme altitude. The first study under altitude conditions is a recent comparison of doubly labeled water with intake balance during strenuous exercise at 2,200-2,550 m, which shows acceptable agreement if corrections are made for changes in baseline isotopic abundances (11). Baseline isotope levels in the Alps were close to sea level values, because subjects drank lowland water. On Mt. Everest, baseline isotope levels were markedly decreased compared with the values from the Alps, probably because of the use of water from melted snow. However, the levels did not decrease over time in the control subjects; the new baseline apparently had stabilized before the subjects were dosed, allowing the calculation of ADMR without corrections for a changing baseline. Another potential source of error in calculations of CO, production from isotope turnover is physical fractionation. Breath water vapor and insensible cutaneous water loss are isotopically fractionated. We used the appropriate correction factors to overcome these errors under lowland conditions. Breath water vapor loss is higher at high altitude than at sea level because of a higher ventilation rate, and lower water vapor partial pressure and temperature of the inspired air. When the amount of CO, produced was used, the mean breath
CLIMBING
MT.
EVEREST
water loss at altitude was 660 ml/day, estimated from the formula from Ferrus et al. (4). On the other hand, insensible cutaneous water loss, estimated at 170 ml/day (5), was lower because of nearly full and permanent clothing, adapted to the environmental conditions. Thus the rate of isotopically fractionated water loss was comparable to lowland conditions. The calculated water loss of the subjects was 2.5-3.9 l/day, only slightly higher than at sea level. Water intake, ranging from 1.8 to 2.9 l/day, did not cover water loss. However, metabolic water production was high. At the measured high levels of energy expenditure, calculated metabolic water production was 0.5 l/day. In addition, humans at high altitude typically lose body mass and body water. Thus there was no systematic discrepancy between reported water intake and calculated water needs. Converting CO, production to energy expenditure, we used the energy equivalent of CO, for an average diet with 40 en% fat, lo-15 en% protein, and 45-50 en% carbohydrate. Although the subjects consumed a low-fat diet, their actual energy-substrate utilization was higher in fat and protein because of the mobilization of body stores. There are indications that RMR may be higher after a change from low to high altitude (7, 8, 18). However, measured RMR at altitude was not systematically different from predicted values for sea-level conditions. Roza and Shizgal (17) estimate the precision of the Harris Benedict equation for predicting RMR to be 14%. The change in RMR after a change from low to high altitude is likely to be smaller. The activity level of the subjects, as reflected in ADMR-to-RMR ratios, was surprisingly high. ADMR/ RMR values normally range between 1.5 and 1.8 for light to moderately active subjects (27). In the present study, ADMR/RMR was higher in all subjects and comparable to the value observed in highly active subjects at sea level engaged in endurance exercise like long-distance running (22). At sea level, sustained metabolic scope in mammals, defined as the maximal energy expenditure that can be sustained indefinitely, ranges from 1.5 to 5.0, depending on the characteristics of the animal (14). In humans, values up to 5.0 have been reported in highly trained cyclists participating in the Tour de France (25) and seem to be the maximum attainable for humans in sea-level conditions. At altitude, the decrease in barometric pressure severely limits the availability of 0, and, as a consequence, maximum 0, uptake (VO,,,) decreases as a function of altitude. This probably limits the sustained metabolic scope attainable at altitude. Using measured EI, RMR, ADMR, and the activity diaries, we could estimate energy expenditure during climbing activities by calculating ADMR minus resting energy expenditure [calculated by adding 20% of basal metabolic rate (BMR) during daytime for arousal, dietinduced thermogenesis, and sedentary activity]. Thus climbing resulted in an extra energy expenditure of 6.6 MJ/day. The average time spent climbing on Mt. Everest was 3.5 h/day. If these two numbers are combined and an energy equivalent of 20 kJ/l 0, is used, the 0, consumption during climbing could then have been 29.6
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ENERGY
EXPENDITURE
ml 1 min-l . kg-‘. This would be at vo 2maxas measured in elite climbers
50-60% of sea-level (13). Such a level is probably near the maximum aerobic capacity at those altitudes and is compatible with the subjects’ sense of intensive exertion while climbing Mt. Everest. On the whole, it seems likely that the sustained metabolic scope at altitude is lower than at sea level. It is noteworthy that subject 5, whose ascent to the summit was included in the observation interval and who had already climbed Mt. Everest twice without supplementary O,, reached the highest VO, (33.6 ml min-’ kg-l). The discrepancy between EI and ADMR was related to the loss of FM. The mean energy equivalent of weight loss was 31 MJ/kg, within the range of 28-32 MJ/kg for two-thirds fat and the remainder only water or only protein, respectively. Thus the energy balance equation fits: EI = EE - ABM. In cone lusion, the results from this study show the prob lems of the maintenance of energy balan .ce du ring high-altitude climbing. EI is low, whereas energy expenditure is equivalent to values that are found only in endurance athletes at sea level.
CLIMBING
l
l
l
We thank the participants of the study: Christine Janin, Pascal Tournere, Marie Guilaine Jesenne, Erik Decamp, and Marc Battard; Dr. Christine Janin, who supervised the measurements during climbing; Loek Wouters, who did the isotopic analysis of the samples; and Nicole Duysens, who analyzed the food records. The cost of the doubly labeled water was covered by an Isostar Research Grant from Sandoz Nutrition, Bern, Switzerland. Federation Francaise pour la Montagne et 1’Escalade partly funded the observations in the Alps, and we were given permission to use the Italian Research Laboratory near basecamp during the Mt. Everest expedition. Address for reprint requests: K. R. Westerterp, Dept. of Human Biology, University of Limburg, PO Box 616,620O MD Maastricht, The Netherlands. Received 4 September 1991; accepted in final form 5 June 1992. REFERENCES S. J., AND F. D. BLUME. Weight loss and changes in body composition at high altitude. J. Appl. Physiol. 57: 1580-1585,1984. 2. DURNIN, J. V. G. A., AND J. WOMERSLEY. Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years. Br. J. 1. BOYER,
Nutr. 32: 77-97, 1974. 3. FERRETTI, G., H. HAUSER,
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tion in men living at 5,800 m (19,000 ft). J. Appl. Physiol. 19: 949954,1964. GROVER, R. F. Basal oxygen uptake in man at high altitude. J. Appl. Physiol. 18: 909-912, 1963. GUILLAND, J. C., AND J. KLEPPING. Nutritional alterations at high altitude in man. Eur. J. Appl. Physiol. Occup. Physiol. 54: 517-523, 1985. HARRIS, J. A., AND F. G. BENEDICT. A Biometric Study of Basal Metabolism in Man. Washington, DC: Carnegie Institution, 1919. HOYT, R. W., T. E. JONES, T. P. STEIN, G. W. MCANINCH, H. R. LIEBERMAN, E. W. ASKEW, AND A. CYMERMAN. Doubly labeled
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K. R., W. H. M. SARIS, M. VAN Es, AND F. TEN the doubly labeled water technique in humans during heavy sustained exercise. J. Appl. Physiol. 61: 2162-2167,1986. 26. WESTERTERP, K. R., W. P. H. G. VERBOEKET-VAN DE VENNE, G. A. L. MEIJER, AND F. TEN HOOR. Self-reported intake as a measure for energy intake: a validation against doubly labelled water. In: Obesity in Europe, edited by G. Ailhaud, B. Guy-Grand, M. Lafontan, and D. Ricquier. London: Libbey, 1992, p. 17-22. 27. WORLD HEALTH ORGANIZATION. Energy and ments: Report of a Joint FAOIWHOKJNU Expert
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