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The Journal of Nutrition Vol. 128 No. 1 January 1998,
pp. 50-55
Beltsville Human Nutrition Research Center, U.S. Department of Agriculture, Beltsville, MD 20705; * College of Business and Management, Cardinal Stritch University, Milwaukee, WI 53217 and Department of Military and Emergency Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
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ABSTRACT |
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Abstract
Introduction
Methods
Results
Discussion
References
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The objectives of the study were to determine total energy intakes, distribution of energy derived from the macronutrients, and the effects of increasing altitudes on energy and macronutrient consumption during exposure to high altitudes. High fat, low carbohydrate diets (35% and 50% of energy, respectively) or low fat, high carbohydrate diets (20% and 65% of energy, respectively) were provided to two groups of subjects for a 3-wk period. Groups then consumed the alternate diet for 3 wk, followed by a return to the original diet for the remaining 3 wk of the study. Free choice of individual items and amounts within each diet was permitted. Intake of food and fluid was determined by means of monitored entries in daily food records. Five subjects remained at Base Camp (5300 m) and 10 subjects climbed to altitudes up to and including the summit of Mt. Everest (8848 m). Subjects consumed an average of 10.22 ± 4.57 MJ/d (2442 ± 1092 kcal) energy while at Base Camp, with climbers consuming significantly more than Base Camp personnel [11.89 ± 4.88 vs. 7.87 ± 2.98 MJ/d (2841 ± 1167 vs. 1881 ± 713 kcal/d), P 
0.0001]. There was a significant decline in energy consumption at increasing altitudes (P = 0.022), but no shift in distribution of energy provided from fat, carbohydrate or protein (P > 0.05). Contrary to previous reports, subjects in this study did not shift their food selections away from the high fat items towards high carbohydrate items.
"The importance of adequate caloric and fluid intake must be rated at least as highly as that of oxygen" (Pugh 1965 Several of the early studies related to food and nutrient intakes at high altitude reported changes in taste perception (Anonymous 1938, Pugh 1954 An increasing number of people are traveling to higher altitudes for sport or recreation, with the duration of such sojourns lasting upwards of several months. Food intakes (Askew 1989 Subjects.
The research design was reviewed and approved by the Georgetown University Medical School Human Use Committee and by the U.S. Department of Agriculture Human Studies Committee. Prior to acceptance into the expedition, the full extent of the research to be conducted was explained, both verbally and in writing, to the potential subjects. Following this explanation, written informed consent was obtained from each subject. All subjects, including two Base Camp personnel with no previous high altitude experience, agreed that their participation in the research to be conducted presented minor inconveniences and risks compared with the normal risks associated with an expedition to the environs of Mt. Everest.
Location and time of study.
Subjects assembled in Kuala Lumpor, Malaysia, in mid-February, 1989. Most climbed to the summit of Mt. Kinabalu (4070 m) on the island of Borneo as a conditioning exercise and then flew into Kathmandu, Nepal (1350 m) in late February. Three days after arrival in Kathmandu, subjects flew into the village of Lukla (2900 m) and hiked into Mt. Everest Base Camp (5300 m) over a 10-d period. From Base Camp, Camps I-IV were established at altitudes of 5910 m, 6440 m, 7120 m, and 8000 m, respectively. The nutrition research began on March 13 and concluded on May 14, with the expedition departing Base Camp on May 22.
Dietary protocol.
Two diets of three meals and daily snacks on a 10-d rotation were prepared, which differed in the percent of energy derived from fat and carbohydrate, with protein energy being held constant. The goal of Diet A was to provide a menu that contributed 35% energy from fat, 50% from carbohydrate and 15% from protein. The goal of Diet B was to provide a menu that contributed 20% energy from fat, 65% from carbohydrate and 15% from protein. Each daily menu was designed to provide approximately 27.2 MJ per person, supplemented with 2.1 MJ from an array of glucose polymer beverages.
Selection of foods for inclusion in Diets A and B.
The foods which were chosen to be consistent with the goals of Diet A and Diet B were carefully selected based on the following criteria: 1) Each food item which was intended to be eaten as packaged was placed in a Source of foods.
Following the final selection of foods that were consistent with the goals of Diet A or Diet B, and which met the above described selection criteria, 32 sources were identified. Approximately one-third of the foods were commonly available at grocery stores, one-third were freeze-dried foods and one-third were commercial retort foods. The commercially-available retort foods were precooked and sealed in foil pouches, ready to be dropped into boiling water for final heating at the time of consumption. Consumption was either directly from the foil pouch or from a bowl.
Preparation of foods.
At Base Camp, foods for Diet A and Diet B were selected from the storage area the night before preparation. Throughout the day, the food was prepared by local cooks under the supervision of one of the authors (JAL), a registered dietitian, to ensure that the instructions of the manufacturer were followed and that the proper food was served to each group of subjects. At Camp II, a Nepalese cook trained by JAL in Base Camp prepared the foods requested by the subjects. At Camps I, III and IV, the food was selected and prepared by the subjects. At all camps, ice was melted over the stoves to provide water for drinking and for preparation of the foods, as necessary.
Diet records.
For the entire 9-wk study period, all subjects completed a daily food record, irrespective of the altitude reached. For the purposes of this study, a customized food record was devised to facilitate the recording of foods actually consumed by the subjects. The food record was divided into major sections of drinks, cereals, breads and crackers, soups, miscellaneous, entrees, desserts and snacks. For each section, the portion sizes were listed such that the subjects needed only to indicate with a check mark the number or amount of each food item consumed. The researchers were primarily interested in documenting the daily intake of foods and nutrients recorded from midnight to the following midnight. As such, time of day or at which meal the food was consumed was not recorded. All foods and quantities consumed were entered on the diet records and monitored on site by a registered dietitian and by the study director.
Calculation of energy intake and distribution.
Upon return to the United States, data from the food records were entered into Paradox v. 4.0 relational database program (Borland Associates, Scotts Valley, CA), and the daily intake of nutrients were calculated using the MedQ food database (MedQ, Vienna, VA). This database contains numerous freeze-dried foods and other unique foods which have been used by the U.S. Military in previous nutrition research mountain expeditions. Several additional items were entered into the MedQ database. The nutrient intakes calculated were energy (MJ), protein, carbohydrate, fat, crude fiber, water, alcohol, calcium, phosphorus, magnesium, iron and zinc. The relative energy contributions from protein, carbohydrate, fat and alcohol, and the food quotients (FQ)3 were also calculated. The FQ is equivalent to the respiratory quotient of the food consumed, which is the ratio of CO2 produced/O2 consumed in the oxidation of all metabolizable fuels (Black et al. 1986
Statistical analysis of data.
Means, standard deviations (SD) and significance of differences among pairs of data sets were calculated by Student's unpaired two-tailed t-test with the Instat statistical program (GraphPad Software, San Diego, CA). Relation of dietary energy intake with altitude was determined by Person's ranked correlation. Statistical significance was set at P All subjects but one lost body weight during the expedition (Table 1), ranging from a gain of 1.6 kg (subject 5B) to a loss of 10.8 kg (subject 3C). However, none of the weight losses were considered to be excessive for exposure to the altitudes experienced. The subject who gained weight (subject 5B) was recovering from pneumonia immediately prior to departing the U.S. and chose to stay at Base Camp for the duration of the study. Subject 3C, who lost the most weight, reached an altitude of approximately 8,200 m near the end of the expedition, which established at that time a world record altitude for his age (57 y).
Living and working at high and extreme altitudes present many unique challenges, including that of providing suitable foods that are palatable, that will be consumed by the subjects, and that contain the macronutrients to provide energy approaching the amount utilized. Some of the environmental and psychological challenges are hypoxia, cold, extreme work requirements, exposure to life-threatening dangers, prolonged separation from family and friends, and lack of fresh or commonly-consumed foods. The impact of each of these stresses on physical performance and psychological well-being is difficult to discern when all are imposed simultaneously, as occurs during an actual mountain-climbing expedition. The U.S. Army Research Institute of Environmental Medicine (Houston et al. 1991 Special appreciation is expressed to the following companies which generously donated items or services for use during this study. Without their cooperation and enthusiasm, this study could not have been conducted. Alpine Aire, Nevada City, CA; Boyd Coffee, Portland, OR; Campbell's Soup, Camden, NJ; Coleman Stove, Wichita, KS; Colorado Beekeepers Association, Colorado Springs, CO; Diamond Crystal, Wilmington, MA; Dri-Lite Foods, Redding, CA; Hershey Chocolate, Hershey, PA; Honey Acres, Ashippon, WI; Idaho Fresh-Pak, Lewisville, ID; Malaysian Airlines, Kuala Lumpor, Malaysia; McCormick Spices, Hunt Valley, MD; Morinaga Nutritional Food, Compton, CA; Nabisco Brands, East Hanover, NJ; Nestlé, Glendale, CA; Nugget, Inc., Stockton, CA; Oscar Mayer, Madison, WI; Pepperidge Farms, Norwalk, CT; Provesta Corporation, Bartlesville, OK; Quaker Oats, Chicago, IL; Recreational Equipment Inc., Seattle, WA; Ross Laboratories, Columbus, OH; and Truitt Bros, Salem, OR. The assistance of Sheri Henderson, who played a major role in obtaining, cataloging and packing the food items, is also appreciated. Sincere appreciation is expressed to selected personnel at the U.S. Embassy, Kathmandu, whose generous and innovative efforts made this entire study possible.
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
). Although those words were published more than 30 years ago, the majority of research on humans working and living at high and extreme altitudes has focused on measurements related more to physiology than to nutrition. Until recently the scientific literature contained limited reports on actual energy consumption at high altitude relative to the macronutrients, including the effects of increasing altitudes on the consumption of these nutrients and energy. Some of the earlier studies used anecdotal reports, records of food intakes for total man-days rather than per climber, or diet history or records of food intakes for a few subjects (Anonymous 1938, Pugh 1954, Tillman 1948). More recent studies were conducted at modest altitudes (Consolazio et al. 1972, Edwards et al. 1991) or were conducted for a short duration (Edwards et al. 1991, Guilland and Klepping 1985, Westerterp 1992).
, Tillman 1948), perhaps due to ketosis (Anonymous 1938). In an anonymous article (1938), Shipton stated that at 27,000 ft on Mt. Everest, it is "impossible to induce an appetite of any sort. All solid food is nauseating." This change in taste perception reportedly led predominantly to a diminution of fat intake. Shipton (Anonymous 1938) stated, "one does not crave for fat at an elevation of 12,000 feet, and I don't think you could eat more than a restricted amount of it. That necessitates cutting down the fat and substituting instead carbohydrate foods." This statement has remained unchallenged through the ensuing six decades, and has become a standard guideline in planning foods for advanced camps at high and extreme altitudes.
, Consolazio et al. 1972, Guilland and Klepping 1985, Hannon et al. 1976) and body composition (Boyer and Blume 1984, Butterfield et al. 1992, Fulco et al. 1985, Kayser 1992, Kayser et al. 1993, Krzywicki et al. 1969, Surks et al. 1966, Westerterp et al. 1992) are affected by increasing altitudes. It is important to determine the actual total energy and the specific macronutrients consumed in order to provide guidelines for a suitable selection of nutritious foods which could be consumed at these altitudes. Accordingly, a nutrition research mountain climbing expedition to Mt. Everest was conducted. All climbers were subjects in the study, and all subjects participated daily in the research for the duration of the expedition. The goals of this study were to determine, as accurately as possible, the intake of foods at increasing altitudes, the resulting energy provided by these foods, the macronutrient composition of these foods, the energy expended, and the changes in body composition during the expedition. This report focuses on energy and macronutrient intakes and the effects of increasing altitude on such intakes.
MATERIALS AND METHODS
Abstract
Introduction
Methods
Results
Discussion
References
, Rose et al. 1988) without the necessity of regard for climbing experience or ability. The research subjects consisted of five women and 10 men from the United States, Mexico and The Netherlands. Ages of the subjects ranged from 23 to 64 y (Table 1). All were in excellent physical condition prior to departure, except for one man who was recovering from pneumonia (5B) and one woman who had half of one lung which was noncommunicating (3B). Both of these subjects remained at Base Camp (5300 m) for the duration of the expedition, with occasional excursions to lower altitudes for health-related reasons. Several subjects were professional mountain guides, others were recreational climbers, with the remainder having assisted previous expeditions or being recruited specifically to assist in the research portion of the expedition. Only those 10 subjects with extensive previous high altitude mountaineering experience were permitted to enter and climb in the Khumbu Icefall above Base Camp and, thus, to reach altitudes at or above that of Camp I (5910 m). The other five subjects remained at Base Camp for the duration of the expedition, with occasional day hikes to lower or higher altitudes, never exceeding 5600 m.
View this table:
Table 1.
Physical description and total average daily reported energy intake of subjects
20°C freezer for 2-4 d and then removed and tested immediately by the authors for ease of chewing. Several foods containing chocolate, caramel or nougat were very hard and brittle at this temperature and were not included due to concern over breaking teeth or extraction of dental fillings. 2) All items were rated at sea level according to palatability by two of the authors (MPH, RDR). Only those items which were rated high by both testers were included. 3) For those items which required cooking, careful attention was given to the difficulty of preparation in an aluminum pot over a single burner stove while in a small tent. The amount of water necessary for preparation, which could only be provided from melting of snow and ice, was a serious consideration. Items which necessitated either extensive cleaning or the use of excess water to clean cooking utensils were eliminated. For these items that were tested, preparation instructions were followed exactly as provided on the package by the manufacturer. 4) Items which required excessive cooking time at sea level were excluded to conserve fuel while at high altitudes. 5) Items which had either a short shelf life or which required refrigeration were not included. Although this latter concern might seem inconsistent with an expedition to Mt. Everest, all foods were temporarily stored in and shipped through Kuala Lumpor and Bangkok, which may have resulted in spoilage since both cities are in the tropics.
), care was taken to provide adequate spices for self-selection. No additional salt was provided due to the high sodium content in many of the prepackaged food items, and salt-substitute packets were made available. It was noted that following initial complaints of lack of salt, the subjects gradually became accustomed to using the spices, with little consumption of the salt-substitute.
, Roberts et al. 1991). The FQ is derived from the weighted average of the amount of carbohydrate (FQ = 1.00), protein (FQ = 0.83) and fat (FQ = 0.71) present in each food item (Black et al. 1986).
View this table:
Table 2.
Effect of increasing altitude on calculated total energy intakes of climbers as reported on food records1
0.05 for all comparisons.
RESULTS
Abstract
Introduction
Methods
Results
Discussion
References
0.05).
0.05). This indicates, as in the case for energy consumption at Base Camp, that those climbers who reached Camp IV and above did not have significantly different energy consumptions than those who did not reach such altitudes. The food quotients did not differ at increasing altitudes.
View this table:
Table 3.
Effect of altitude on distribution of energy provided by the macronutrients in food consumed by high altitude climbers
and base camp personnel1
View this table:
Table 4.
Increasing contribution of high fat and high carbohydrate foods to total energy intake by climbers and base camp personnel as a function of increasing altitude
DISCUSSION
Abstract
Introduction
Methods
Results
Discussion
References
) utilized a hypobaric decompression chamber to isolate and study the effects of hypoxia, but such protocols are not able to duplicate free-living environmental and physical performance conditions. Thus, it is necessary to utilize actual mountainous conditions to discern the full impact on human performance. The results obtained from this study provide the longest and most comprehensive description of macronutrient intakes during an actual high and extreme altitude expedition.
, Fulco et al. 1985). When the climbers reached Camp IV at the South Col between Lhotse and Mt. Everest, the food quotients (Table 2) and energy distribution (Table 3) more closely resembled those at Camps I and II.
). He also observed that "the degree of underreporting increases with intake." Recently, Heymsfield et al. (1995) presented five reasons for such chronic underreporting of actual intakes, which included inadequate education, inaccurate food-size estimates, memory disturbance, psychosocial motivation, and inaccurate food labeling. Due to the reported decrease in cognitive functions at increasing altitude (Townes et al. 1984), it is likely that the subjects in the present study also underreported their actual food intakes. Thus, the intakes reported in this manuscript may best be assumed to be a minimum consumed rather than the exact amount consumed. This is an inherent problem in conducting nutrition studies under field conditions and it is likely that other expeditions suffered from similar, if not worse, underreporting of food intakes.
, Boyer and Blume 1984, Consolazio et al. 1972, Lickteig 1990), but are consistent with observations derived during the conduct of Operation Everest II (Houston et al. 1991, Rose et al. 1988) in a hypobaric decompression chamber. Among many mountain climbers, it is commonly assumed that there is a natural increasing preference for consumption of higher carbohydrate foods at the highest altitudes. This assumption may result from anecdotal stories (Anonymous 1938) rather than from a careful consideration of scientific observations conducted under professional dietary supervision.
ACKNOWLEDGMENTS
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FOOTNOTES |
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Manuscript received 23 June 1997. Initial reviews completed 11 August 1997. Revision accepted 25 August 1997.
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LITERATURE CITED |
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Abstract
Introduction
Methods
Results
Discussion
References
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