There are many questions when it comes to diet & nutrition at high altitude.
Everyone knows that plenty of water needs to be consumed when at high
altitude - somewhere around 3-4 liters a day. However, when it comes to
diet, many questions are often asked:
Here is some information that will, hopefully, help answer some nutrition questions.
From Body Results outdoor sports strength & conditioning
Studies show that our bodies can process fats and carbohydrates normally up to 5000 meters (16,400 ft), so any loss below that elevation can be attributed to less than adequate intake. Above 5000 meters, however, weight loss seems to be unavoidable, due to several factors: 1) loss of appetite and increased nausea from the effects of altitude sickness; 2) change in overall metabolism; and 3) the body's inability to digest food.
The average-sized male climber can expect to burn upwards of 500-800 calories per hour at higher altitudes (the higher numbers are for difficult carry days) so plan on consuming substantially more than you eat back home. A good ratio seems to be 60-70% carbohydrates, 15-20% from fat and 15-20% from protein. Complex carbohydrates provide the ongoing fuel needed to replenish glycogen stores, while protein helps prevent excess deterioration of lean muscle mass. Beware the very high-fat diet at altitude: reliance on foods such as typical mountaineers' classics like Snickers bars, cheese, jerky, nuts, and so forth can result in chronic muscular fatigue, since a high-fat diet lacks the necessary level of readily-available carbohydrates; furthermore, high-fat diets require more oxygen during metabolism for processing, thus slowing down acclimatization.
The simplest answer to this is: what you'll eat, consistently, and a lot of it. Make sure you test-run your food ahead of time on training climbs (on Rainier and other similar training climbs that take you above 12.500') so you learn what works best for you. By all means, take foods and beverages you enjoy or you won't want to eat them. If you know that your water treatment makes drinking unpleasant, take flavored drink mixes like Tang, cocoa or Gatorade to help mask the taste and add valuable carbohydrates. Also consider the weight of all the food (especially if you're going to be carrying most of it yourself!) -- dehydrated foods that are light weight but calorically dense are highly desirable. Potato buds that you can mix with dried turkey or other meat and hot water seems to be a concoction that goes down pretty easily for most people at high altitude. But if you absolutely hate the taste of any of your fare at sea level, leave it behind.
Resource: Burnik and others, in Ch. 6, Some Anthropometric Changes on Extreme High Altitudes, Science of Climbing and Mountaineering CD-ROM, available through Human Kinetics. Research done on Everest, North Base Camp, 1997.
E. Wayne Askew, PhD
Wayne is professor of Foods and Nutrition at the University of Utah, Salt
Lake City, UT, USA.
http://www.wms.org/education/Nutrition
Inappropriate thirst and appetite responses, together with increased insensible water loss, transient diuresis and increased energy expenditures can lead to rapid dehydration and glycogen depletion and weight loss at altitude if adequate food and fluid are neglected. Dehydration may intensify the symptoms of altitude sickness and result in even lower food intakes. One of the most effective and practical performance-sustaining measures that can be adopted upon arrival at high altitude is to consume a minimum of 3 to 4 liters of fluid per day containing 200 to 300 g of carbohydrate in addition to that contained in the diet. This should prevent dehydration, improve energy balance, improve the oxygen delivery capability of the circulatory system, replenish muscle glycogen, and conserve body protein levels.
Effect of altitude on energy balance
Food intakes are typically reduced 10 to 50% during acute altitude exposure depending upon the individual and rapidity of ascent. Rose et al. (1988) observed depressed food intakes and weight loss at altitude even under the controlled hypobaric chamber conditions of Operation Everest II. In this study, work requirements were relatively low, and a thermoneutral hypobaric environment with an adequate quantity and variety of palatable food were provided. Decreased food intake under these conditions indicated that hypoxia by itself was a major factor reducing appetite and food intake. Adequate food intake can be achieved at altitude but it requires a concerted, conscious effort of dietary management and forced eating (Butterfield 1996). The combination of anorexia and reduced food intake can potentially exert a negative effect on work performance at even moderate altitude (Askew 1996).
Numerous pharmacological attempts to reduce acute mountain sickness have been investigated, with limited success. Caffeine has been reported to enhance relatively short-term, high-intensity work at simulated high altitude, perhaps via an influence upon blood glucose availability. High carbohydrate diets have been recommended by some as a "non-pharmacological" method to reduce the symptoms associated with acute mountain sickness. As an adjunct for lessening or preventing altitude illness, high carbohydrate diets should be fed prior to and during the initial 3 to 4-day critical period of acute altitude exposure. It should be noted that only a limited number of investigators have studied high-carbohydrate diets or carbohydrate supplements for the relief of acute mountain sickness and performance enhancement. Some (Consolazio et al. 1969; Askew 1997), but not all (Swenson et al. 1997), have reported some beneficial effects upon symptoms, mood, and performance. Most investigators agree that, at the very least, energy balances can be improved by aggressive carbohydrate supplementation at altitude, particularly via the fluid component of the diet. In addition to improving energy balance, carbohydrate supplementation also improves nitrogen balance in the initial phase of acute altitude exposure. Butterfield et al. (1992) have confirmed that the negative nitrogen balance encountered at altitude is not due to any hypoxia-related decrease in protein digestibility or absorption, but primarily due to a negative energy balance.
The mechanism by which carbohydrate exerts a beneficial effect on relieving symptoms of altitude sickness and prolongs endurance at altitude may be related to improving blood oxygenation. Hansen et al. (1972) showed that blood oxygen tension is increased by a high-carbohydrate diet and Dramise et al. (1975) reported that carbohydrate can increase lung pulmonary diffusion capacity at altitude. Recently, Lawless et al. (1999) have demonstrated that carbohydrate consumption significantly increased oxygen tension and oxyhemoglobin saturation in arterial blood of subjects during simulated altitude (reduced oxygen in inspired air). In addition to improving blood oxygenation, carbohydrate is a more "efficient" energy source at altitude than fat or protein. The energy production per liter of oxygen uptake is greater when carbohydrate is the energy source compared to fat (carbohydrate, 5.05 kcal/l O2; fat, 4.69 kcal/l O2) regardless of the oxygen tension in the inspired air. Taken together, these different lines of evidence suggest that carbohydrate is a more efficient energy source for work at reduced oxygen tension.
Fluid requirements at altitude
Water requirements at altitude may be greater than those at sea level, due to the low humidity of the atmosphere at altitude and hyperventilation associated with altitude exposure (Hoyt and Honig 1996, Askew 1996). The risk of dehydration is high at altitude due to diuresis and water loss in breath and sweat, coupled with the difficulty of obtaining adequate water. An inappropriate thirst response coupled with an increase in insensible water loss and a transient diuresis during the initial hours of altitude exposure, can result in rapid dehydration if adequate fluid is either unavailable or neglected. The rate of respiratory water loss at altitude is about twice the rate of respiratory water loss for an equivalent activity at sea level (Milledge 1992).
Aviat Space Environ Med. 2002 Aug;73(8):758-65.
Energy intake deficit and physical performance at altitude.
Fulco CS, Friedlander AL, Muza SR, Rock PB, Robinson S, Lammi E, Baker-Fulco CJ, Lewis SF, Cymerman A.
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Natick, MA 01760-5007, USA. charles.fulco@na.amedd.army.mil
BACKGROUND: Physical performance of sea-level (SL) residents acutely
exposed to altitude (ALT) is diminished and may improve somewhat with ALT
acclimatization.
HYPOTHESIS: A large reduction in lean body mass (LBM),
due to severe energy intake deficit during the first 21 d of ALT (4300 m)
acclimatization, will adversely affect performance.
METHODS: At ALT, 10
men received a deficit (DEF) of 1500 kcal x d(-1) below body weight (BW)
maintenance requirements and 7 men received adequate (ADQ) kcal x d(-1) to
maintain BW. Performance was assessed by: 1) maximal oxygen uptake
(VO2max); 2) time to complete 50 cycles of a lift and carry task (L+C); 3)
number of one-arm elbow flexions (10% BW at 22 flexions x min(-1); and 4)
adductor pollicis (AP) muscle strength and endurance time (repeated 5-s
static contractions at 50% of maximal force followed by 5-s rest, to
exhaustion). Performance and body composition (using BW and circumference
measures) were determined at SL and at ALT on days 2 through 21.
RESULTS: At SL, there were no between-group differences (p > 0.05) for any
of the performance measures. From SL to day 21 at ALT, BW and LBM declined
by 6.6 +/- 3 kg and 4.6 kg, respectively, for the DEF group
(both p < 0.01), but did not change (both p > 0.05) for the ADQ group.
Performance changes from day 2 or 3 to day 20 or 21 at ALT were as follows
(values are means +/- SD): VO2max (ml x min(-1)): DEF = +97 +/- 237,
ADQ = +159 +/- 156; L + C (s): DEF = -62 +/- 35*, ADQ = -35 +/- 20*
(*p < 0.05; improved from day 3); arm flex (reps): DEF = -2 +/- 7,
ADQ = +2 +/- 8; AP endurance (min): DEF = +1.4 +/- 2, ADQ = + 1.9 +/- 2;
AP strength (kg): DEF = -0.7 +/- 4, ADQ = -1.2 +/- 2. There were no
differences in performance between groups.
CONCLUSIONS: A significant BW
and LBM loss due to underfeeding during the first 21 d of ALT
acclimatization does not impair physical performance at ALT.
J Appl Physiol. 2000 Jan;88(1):246-56.
Women at altitude: carbohydrate utilization during exercise at 4,300 m (14,000 ft.)
Braun B, Mawson JT, Muza SR, Dominick SB, Brooks GA, Horning MA, Rock PB, Moore LG, Mazzeo RS, Ezeji-Okoye SC, Butterfield GE.
Aging Study Unit, Geriatric Research, Education, and Clinical Center, Veterans Affairs Health Care System, and Division of Gerontology, Endocrinology, and Metabolism, Stanford University Medical School, Palo Alto, California 93404, USA.
To evaluate the hypothesis that exposure to high altitude would reduce blood glucose and total carbohydrate utilization relative to sea level (SL), 16 young women were studied over four 12-day periods: at 50% of peak O(2) consumption in different menstrual cycle phases (SL-50), at 65% of peak O(2) consumption at SL (SL-65), and at 4,300 m (HA). After 10 days in each condition, blood glucose rate of disappearance (R(d)) and respiratory exchange ratio were measured at rest and during 45 min of exercise. Glucose R(d) during exercise at HA (4.71 +/- 0.30 mg. kg(-1). min(-1)) was not different from SL exercise at the same absolute intensity (SL-50 = 5.03 mg. kg(-1). min(-1)) but was lower at the same relative intensity (SL-65 = 6.22 mg. kg(-1). min(-1), P < 0.01). There were no differences, however, when glucose R(d) was corrected for energy expended (kcal/min) during exercise. Respiratory exchange ratios followed the same pattern, except carbohydrate oxidation remained lower (-23.2%, P < 0.01) at HA than at SL when corrected for energy expended. In women, unlike in men, carbohydrate utilization decreased at HA. Relative abundance of estrogen and progesterone in women may partially explain the sex differences in fuel utilization at HA, but subtle differences between menstrual cycle phases at SL had no physiologically relevant effects.
See PDF file for full article
J Appl Physiol. 2000 Jan;88(1):272-81.
Women at altitude: energy requirement at 4,300 m (14,100 ft).
Mawson JT, Braun B, Rock PB, Moore LG, Mazzeo R, Butterfield GE.
Palo Alto Veterans Affairs Health Care System, Palo Alto, California 94304, USA.
To test the hypotheses that prolonged exposure to moderately high altitude increases the energy requirement of adequately fed women and that the sole cause of the increase is an elevation in basal metabolic rate (BMR), we studied 16 healthy women [21.7 +/- 0.5 (SD) yr; 167.4 +/- 1.1 cm; 62.2 +/- 1.0 kg]. Studies were conducted over 12 days at sea level (SL) and at 4,300 m [high altitude (HA)]. To test that menstrual cycle phase has an effect on energetics at HA, we monitored menstrual cycle in all women, and most women (n = 11) were studied in the same phase at SL and HA. Daily energy intake at HA was increased to respond to increases in BMR and to maintain body weight and body composition. Mean BMR for the group rose 6.9% above SL by day 3 at HA and fell to SL values by day 6. Total energy requirement remained elevated 6% at HA [ approximately 670 kJ/day (160 kcal/day) above that at SL], but the small and transient increase in BMR could not explain all of this increase, giving rise to an apparent "energy requirement excess." The transient nature of the rise in BMR may have been due to the fitness level of the subjects. The response to altitude was not affected by menstrual cycle phase. The energy requirement excess is at present unexplained.
See PDF file for full article.
Aviat Space Environ Med. 1999 Sep;70(9):874-8.
Improvement in hypoxemia at 4600 meters (15000 ft) of simulated altitude with carbohydrate ingestion.
Lawless NP, Dillard TA, Torrington KG, Davis HQ, Kamimori G.
Pulmonary and Critical Care Medicine, Walter Reed Army Medical Center, Washington, DC 20307, USA.
BACKGROUND: Carbohydrate ingestion increases the relative production of
carbon dioxide which results in an increase in ventilation in normal
individuals. An increase in ventilation at altitude can result in
improvement of altitude-induced hypoxemia.
HYPOTHESIS: Carbohydrate ingestion will increase the arterial blood
oxygen tension and oxyhemoglobin saturation during acute high altitude
simulation.
METHODS: There were 15 healthy volunteers, aged 18-33 yr, who
were given a 4 kcal x kg(-1) oral carbohydrate beverage administered 2.5 h
into an exposure to 15,000 ft (4600 m) of simulated altitude (5.5 h after
the last meal). Altitude was simulated by having subjects breath a 12%
oxygen/balance nitrogen mixture while remaining at sea level. Arterial
blood gas samples were drawn at baseline and at regular intervals up to
210 min after carbohydrate ingestion. Subjects were evaluated for AMS by
use of the Environmental Symptoms Questionnaire (ESQ) and a weighted
average of cerebral symptom score (AMS-C).
RESULTS: Baseline PaO2 increased significantly (p < 0.01) from 43.0 +/-
3.0 mmHg at 4600 m before carbohydrate ingestion to 46.8 +/- 6.2 mmHg at
60 min after carbohydrate ingestion. Arterial oxygen saturation rose
significantly (p < 0.01) from a baseline of 79.5% +/- 5.1 to 83.8% +/-
6.42 at 60 min.
CONCLUSIONS: Carbohydrate consumption significantly
increased oxygen tension and oxyhemoglobin saturation in arterial blood
of normal subjects during simulated altitude. Effects reached statistical
significance across all subjects at 60 min. There was no significant
difference in arterial oxygen levels or arterial oxygen saturation in
subjects who developed AMS vs. those who did not develop AMS.
J Nutr. 1998 Jan;128(1):50-5.
Intakes of high fat and high carbohydrate foods by humans increased with exposure to increasing altitude during an expedition to Mt. Everest.
Reynolds RD, Lickteig JA, Howard MP, Deuster PA.
Beltsville Human Nutrition Research Center, U.S. Department of Agriculture, Beltsville, MD 20705, USA. reynolds@uic.edu
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 0.05). Contrary to previous reports, subjects in this study did not shift their food selections away from the high fat items towards high carbohydrate items.
See PDF file for full article
J Am Diet Assoc. 1991 Dec;91(12):1543-9.
Consumption of a dehydrated ration for 31 days at moderate altitudes: energy intakes and physical performance.
Worme JD, Lickteig JA, Reynolds RD, Deuster PA.
Department of Military Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799.
Energy intake, body weight, maximal work capacity, and measures of muscle strength and endurance were obtained from eight men who consumed a high-carbohydrate (CHO) dehydrated ration during a 31-day period of high activity at moderate altitudes. Data were collected 2 months before exposure to moderate altitudes (PRE), multiple times during the month's expedition at moderate altitudes (ALT), and after return from the expedition (RET). Work capacity per kilogram of body weight increased significantly from the PRE phase to the ALT phase. Mean energy intake averaged 2,354 +/- 71, 3,430 +/- 79, and 3,384 +/- 117 kcal/day during PRE, ALT, and RET, respectively; mean CHO intake during ALT was 595 +/- 13 g/day. Mean weight loss and reduction in body fat were significant: 1.9 +/- 0.9 kg and 18.9 +/- 10.1%, respectively. Energy deficits calculated from changes in body weight and composition during ALT ranged from 473 to 963 kcal/day, whereas the energy deficit estimated from the Harris-Benedict equation was only 194 kcal/day. The rigorous physical activity and exposure to moderate altitudes necessitated a high energy intake, approximating 3,800 kcal/day. The results indicate that physical performance and nutritional status are maintained when a high-CHO diet, consisting primarily of commercially available dehydrated foods, is consumed over a 31-day period of rigorous activity. However, weight loss and gastrointestinal distress were noted. These events might be minimized when a dehydrated ration is consumed, if dietary fat is substituted for some of the CHO.