Winter weather and skiing (and other winter sports) have arrived!! To celebrate the season, we are doing two posts on sport nutrition. The first post was last week and discussed the nutritional modifications for cold weather exercise. This week is part 2, nutrition for high-altitude training. Cold weather and high-altitude do not necessarily have to go together BUT that seems to be the way more often than not. Consider all of the recommendations that apply when planning your nutritional intakes.
How is Exercising at High Altitudes Different?
There are several challenges associated specifically with exercising at high-altitude. The definition of “high-altitude” varies depending on the source, however, is usually above 2600m. Importantly, you may notice effects at lower altitudes and it is a sliding scale with a greater physiological response noted as the altitude increases. One group of authors notes that high-altitude affects performance in three ways. 1) Decreased oxygen availability causing tissue hypoxia and a decrease in the function of the heart and lungs. 2) An approximate 3% decrease in exercise capacity for every 300m above 1500m. 3) Sleep deprivation due to poor sleep quality (1).
Altitude can increase energy needed at rest (basal metabolic rate). One study found an increase of 10-17% at 4300 m above sea level as compared to at sea level (2). Higher altitudes >3500m can also suppress appetite resulting in weight loss (3). If weight loss occurs, there will be an increased use of protein as a fuel source. Often this protein comes from the muscles causing them to decrease in size (4). Alpine skiers, snowboarders etc. have to deal with high altitudes and possibly shivering when they are waiting. In light of this, some experts suggest an extra 200 to 300 kcals/day when at altitude (5).
Athletes training at altitude should consume more energy and can do so by increasing intakes of carbohydrates, protein, and fats. Don’t get fooled into thinking only about protein, as adequate carbohydrates are needed to maintain body weight and preserve muscle mass. How much should you eat? That depends on the individual but if you have unwanted weight loss while training at altitude you should increase your energy intakes to bring your weight back up. In this case, you may have to rely on high-fat, high-calorie foods that you would not normally eat at lower altitudes. Exercising at high-altitude will also affect your blood glucose (sugar) levels. At higher altitudes people use greater amounts of blood and muscle glucose at rest and during exercise than at lower altitudes (6). It is recommended that at altitude the diet provide at least 60% of total calories from carbohydrates (1). Carbohydrate intakes greater than 60% may not be beneficial, as a significant amount of fat is probably needed to provide adequate calories. One study using climbers of Mount Everest, found the energy breakdown of their diet was 58% carbohydrate, 30% fat, and 12% protein (7). A more thorough review of macronutrient intakes at altitude has been published.
High altitudes increase the risk for dehydration as they can cause diuresis (excessive peeing) and reduced thirst. The air also tends to be less humid at altitude resulting in increased respiratory water losses. Adding exercise and sweating into the mix increases the need for fluids above and beyond those associated with altitude (8). It has been suggested that athletes training or competing at high-altitude could require fluid intakes as high as 4 -5 litres per day (9). Ultra-endurance athletes such as cross-country skiers could require even greater intakes (10). At altitude, carefully monitor your sweat rate and realize that insensible water loss (water loss you don’t notice through evaporation, breathing etc.) is greater. Use the “pee test” light yellow and voluminous to gauge needs. Consider using sports or electrolyte drinks to replace fluids, as they may improve water retention (11).
Iron can also be a concern, as at higher altitudes there is less oxygen available. In order to cope, the body increases blood volume to improve oxygen carrying capacity. This adaptive mechanism is very useful but requires the production of more erythrocytes (red blood cells), which means more iron (12). Females need to be especially cautious as they have increased iron losses due to menstruation. Focus on foods high in heme-iron (animal products) and add some vitamin C sources to your diet when consuming plant source of iron. For more information on food sources of iron check out the Office of Dietary Supplements fact sheet on iron. If you feel fatigue or other symptoms of an iron deficiency see you physician and have your iron levels tested.
There is also some suggestion that the need for antioxidant vitamins E and C may be greater at altitude (13). At present, there is little research in this area and supplements cannot be recommended. However, athletes should ensure that their diet contains adequate sources of these vitamins. This can be difficult if access to fresh fruits and vegetables is limited.
Nutrient timing strategies at altitude are similar to those discussed in last week’s post on nutrition for cold weather. The only additional concern is to keep in mind that what you want to eat you have to carry. Being physically active at higher altitudes is already challenging enough without carrying extra pounds of food. Try to eat your larger heavier meals prior to going up to altitude and when you come back down in your recovery. Rely on easy to pack, light-weight foods for during exercise.
- Friedlander, AL et al. (2008). Making molehills out of mountains: Maintaining performance at altitude. ASCM Health and Fitness Journal 12 (6): 15-21.
- Butterfield, GE et al. (1999) Nutrient requriements at high altitude. Clinics in Sports Medicine. 18:607-621.
- Kayser, B. (1992) Nutrition and high altitude exposure. International Journal of Sports Medicine. 13: s129-132.
- Kayser, B. et al. (1992) Protein absorption and energy digestibility at high altitude. Journal of Applied Physiology 73:2425-2431.
- Butterfield, GE (1996) Maintenance of body weight at altitude: In search of 500 kcal/day. In B. M. Marriott & S. J. Carlson (Eds), Nutritional needs in cold and in high-altitude environments (pp. 357-378). Washington, DC: national Academy Press.
- Brooks, GA et al (1991) Increased dependence on blood glucose after acclimatization to 4,300 m. Journal of Applied Physiology. 70:919-927.
- Benso A. (2007) Endocrine and metabolic responses to extreme altitude and physical exercise in climbers. European Journal of Endocrinology. 157:733-740.
- Milledge, JS et al. (1992) Salt and water control at altitude. International Journal of Sports medicine. 13:S61-S63.
- Wilber, R. (2004) Altitude training and athletic performance. Champaign, IL: Human Kinetics.
- Ekblom B et al. (2000). Cross-country skiing. In R.J. Maughan (Ed), Nutrition in sport (Vol. 7 pp 656-662): Oxford: Blackwell Science.
- Yanagisawa K. (2012) Electrolyte-carbohydrate beverage prevents water loss in the early stage of high altitude training. The Journal of Medical Investigation 59:102-110.
- Neilsen P et al (1998) Iron supplementation in athletes: Current recommendations. Sports Medicine. 26:207-216.
- Kechijan D. (2011) Optimizing nutrition for performance at altitude: a literature review. J Spec Oper Med. 11:12-7.