Web Exclusive
Nutrition Guidance for Winter Athletes
By Clare Tone, MS, RD
This winter has unleashed record snowfalls and frigid temperatures across the United States. While many athletes move indoors to train when it’s cold outside, others look to winter sports as a way to stay fit and have fun during the season. Exercising outdoors can be a great way to beat the monotony of the gym and can add an excellent cardiovascular component to workouts while providing cross-training for summer activities.
However, athletes exercising in cold weather, at high altitudes, or both have unique nutritional needs. Popular winter sports that require exertion in cold temperatures, sometimes combined with traveling to high elevations, include alpine, cross-country, and skate skiing as well as snowshoeing and back-country ski touring. People participating in any of these sports, whether recreationally or competitively, can benefit from a basic understanding of the body’s metabolic response to cold and altitude.
Research in the field of high-altitude physiology indicates that recreational or competitive athletes exercising at elevations above 6,000 ft or in temperatures under 32˚F should focus on three primary areas of nutrition: energy balance, carbohydrates, and hydration.
It’s estimated that more than 34 million people travel to high altitudes every year, and statistics from Vail Mountain in Colorado indicate that up to 50% of visitors may experience some level of altitude sickness.1,2 As elevation increases, barometric pressure falls, causing a drop in the pressure of oxygen in the air and a corresponding drop in the delivery of oxygen to body tissues, a condition called hypoxia. Altitude sickness is an umbrella term that includes any number of symptoms of hypoxia, such as headaches, anorexia, nausea, vomiting, and malaise. Symptoms can begin to occur around 6,000 ft and persist anywhere from four to seven days or more. Tolerance to lower oxygen varies from person to person, but many people will acclimate after a period of 48 to 72 hours.
Early expeditions to high altitudes, such as mountaineering excursions into the Himalayas, were the first to observe marked body weight and lean body mass losses in expedition members. Similar observations have been noted among contemporary military expeditions in extreme climates. This phenomenon is termed “the cachexia of altitude.”3,4 The degree to which this energy imbalance affects recreational or competitive athletes at altitude is worth investigating. At a high altitude, the body exerts an appetite-suppressing effect, which causes up to a 50% decreased food intake in some people compared with their sea-level intake. Additionally, several factors combine to increase total energy needs in cold weather at altitude. Research reveals a jump in basal metabolic rate of up to 17% at altitude compared with sea level.5 Add to this an estimated 10% to 15% increase in the metabolic cost of working in the cold due to wearing heavier layers of clothing and the small but constant energy requirement to heat and humidify the colder, dryer air and we have a scenario in which athletes must focus on ingesting enough calories throughout the day to support their activity level and glycogen resynthesis.5
Distribution of macronutrients is also important. While carbohydrates are the primary source of fuel to sustain exercise at any elevation, reliance on carbohydrates appears even greater at altitude. Hypoxia results in lower oxygenation of tissues, including those in muscles, the heart, and the brain. Whatever athletes can do to counter hypoxia symptoms is good in terms of both exercise tolerance and performance. Researchers have long observed that carbohydrates offer a beneficial effect when addressing altitude sickness symptoms and have theorized that it relates to improved blood oxygenation.6 We know carbohydrate metabolism contributes relatively more carbon dioxide production than either fats or proteins, and increased carbon dioxide production leads to increased ventilation.
Dietitians working in ICUs are familiar with the reverse of this relationship. In an attempt to help wean patients from ventilators, lower carbohydrate feedings have been utilized to decrease carbon dioxide production, decreasing ventilation demand.7 So it makes sense for high-altitude athletes to increase carbohydrate intake to increase carbon dioxide production, thereby increasing ventilation and oxygen delivery to the blood. Research appears to support this theory. A trial published in 2008 found that feeding a 10% water solution of sucrose (providing 4 kcal/kg of body weight) 40 minutes before acute hypoxic exposure increased carbon dioxide production, ventilation, and heart rate and significantly improved hemoglobin saturation levels at altitude.8
Cold weather does something else that’s unique: It causes the body to shiver to stay warm. Shivering is fueled by carbohydrates—both blood sugar and stored glycogen—while protein and fat are poorly utilized for this purpose. The imperative to maintain core body temperature puts added demand on glycogen stores.5 Finally, in addition to improved blood oxygenation and glycogen resynthesis, basic biochemistry reminds us that carbohydrate is a more efficient energy source at altitude than fat or protein, yielding slightly more kcals per liter of oxygen consumed.4,6 Given the current popularity of high-protein fad diets, reinforcing the role of carbohydrates for athletes traveling to altitude may be a key strategy for both staying well and optimizing performance.
The last, and perhaps most important, component of a healthful training diet for winter athletes is hydration. Dehydration is frequently cited as a major factor in worsening symptoms of altitude sickness.1 Cold, dry air—common in winter and always at altitude—increases water loss via ventilation. In fact, the rate of water lost through breathing at altitude is about twice that for the same activity at sea level.4 Compounding the issue is a diminished thirst response in cold conditions. These factors, combined with a decreased awareness of sweating in cold temperatures, set athletes up to be very prone to dehydration.
These insights lead to straightforward nutrition recommendations for winter athletes exercising at elevations above 6,000 ft who must pay particular attention to hydration, carbohydrates, and total calories. A goal of 3 to 5 liters of fluid intake daily is the minimum; many athletes will require more.1 Carbohydrates should make up 60% of the diet, with an emphasis on complex carbohydrates. Specific guidelines in the literature estimate carbohydrate needs at 8 g/kg of body weight.9 Given the concurrent demand for both water and carbohydrates, an effective strategy is to replete carbohydrates by mixing carbohydrate sweeteners into part of the day’s fluid component. Keep in mind that electrolyte additives in fluid are generally not necessary. Finally, athletes should be reminded to consume meals and snacks frequently throughout the day, planning healthful pocket snacks for the chairlift or on the trail to ensure a steady availability of blood glucose and resynthesis of muscle glycogen for the next days’ activities.
Through attention to hydration and nutrition, it’s possible to not only mitigate the effects of hypoxia and associated symptoms but also improve performance and enjoyment of popular winter activities.
— Clare Tone, MS, RD, is a freelance health and nutrition writer based in the mountains near Boulder, Colo.
References
1. Friedlander AL, Braun B, Marquez J. Making molehills out of mountains: Maintaining high performance at altitude. ACSM Health & Fitness Journal. 2008;12(6):15-21.
2. Vail Resorts Management Company. Vail Mountain FAQ, 1997-2011. Available at: http://www.vail.com/faqdetail/Mountain-Information/Will-I-get-altitude-sickness-Can-I-prevent-or-cure-it.axd. Accessed January 20, 2011.
3. Rose MS, Houston CS, Fulco CS, Coates G, Sutton JR, Cymerman A. Operation Everest. II: Nutrition and body composition. J Appl Physiol. 1988;65(6):2545-2551.
4. Askew EW. Nutrition at high altitude. Wilderness Medicine Society. Available at: http://www.wms.org/news/altitude.asp. Accessed October 2010.
5. Askew EW. Nutrition and performance in hot, cold and high altitude environments. In: Wolinsky I, ed. Nutrition in Exercise and Sport. 3rd edition. Boca Raton, Fla.: CRC Press; 1997:597-619.
6. Braun B. Effects of high altitude on substrate use and metabolic economy: Cause and effect? Med Sci Sports Exerc. 2008;40(8):1495-1500.
7. van den Berg B, Bogaard J, Hop WC. High fat, low carbohydrate, enteral feeding in patients weaning from the ventilator. Intensive Care Med. 1994;20(7):470-475.
8. Golja P, Flander P, Kemenc M, Maver J, Princi T. Carbohydrate ingestion improves oxygen delivery in acute hypoxia. High Alt Med Biol. 2008;9(1):53-62.
9. Armstrong LE. Nutritional strategies for football: Counteracting heat, cold, high altitude, and jet lag. J Sports Sci. 2006;24(7):723-740.