Nutrition tips for exercising in the snow
Thursday, December 21, 2017. Author Dr Haran Sivapalan
Thursday, December 21, 2017. Author Dr Haran Sivapalan
The holiday season is now well upon us and, for some, that means it’s time to grab your skis, snowboards, skates, and sleds and indulge in some winter sports. Depending on where and how you exercise, cold temperatures and high altitudes put additional demands on your body. Consequently, you’ll have to dress, eat, and hydrate differently for winter sports. We explain the science.
If you’re hitting the slopes this winter, you are likely to encounter temperatures anywhere from -25°C to +5◦C. Indoor ice rinks are obviously chilly too: between +5 and +10°C on average. So, whether it’s cross-country skiing in bucolic Nordic countryside or figure-skating at your local ice rink, your physiology will need to respond to a cold environment. As warm-blooded mammals, humans strive to regulate their core body temperature at a constant level – around 37°C (98.6 F). When faced with low temperatures, your body compensates by increasing its basal metabolic rate. This burns more calories and generates heat energy to warm your body: a process is called thermogenesis.
Interestingly, the exact changes in metabolic rate for thermogenesis vary from person-to-person. Compared to those with high basal metabolic rates (BMR), those with naturally lower BMRs experience greater rises in metabolism and therefore burn more calories in cold weather. Your UCP genes play a critical role here. They encode ‘uncoupling proteins’ which dissipate energy from cell respiration as heat. People with faster metabolisms (higher metabolic rates) ‘waste’ more energy as heat under normal conditions. In cold weather, however, such people may rely more on limiting blood flow to their body’s peripheries (vasoconstriction) to prevent heat loss and therefore may suffer from cold hands and feet.
As metabolic rate and energy expenditure rise in cold environments, you may need to increase your carbohydrate intake accordingly. This is especially important when it’s cold enough to induce shivering, which uses up to 5 times as much energy than normal and rapidly expends glycogen stores. Ideally, assuming you dress sensibly, you’ll avoid shivering altogether. After all, as the outdoor enthusiast’s favorite aphorism goes, “There’s no such thing as bad weather, only bad clothing.”
Although dehydration and thirst are more often synonymous with summer sports, fluid intake is just as important in winter. Exercising in the cold has been shown to cause a 3-8% loss in body weight, due to exhaling more water vapor in cold, dry air (respiratory water loss), increased perspiration under warm clothing, and the fact that lower temperatures make you urinate more often (an effect known as ‘cold-induced diuresis’). So, if you’re heading out in the snow this Christmas, make sure you keep well hydrated.
The cold might not be the only climatic factor to contend with this winter. Skiing, snowboarding and other winter sports often take place in alpine environments, situated at altitudes between 2000 and 4000m above sea level. The higher up you go, the thinner the air – there’s less oxygen to breathe. More accurately, the fraction of air that is oxygen stays the same (about 21%), but, owing to lower barometric pressure at high altitude, the number of oxygen molecules inhaled in each breath falls. (It’s to do with Boyle’s Law - if you can remember your high-school physics!)
Fortunately, your body has lots of tricks to survive in low oxygen conditions. If you’ve been up a high mountain before, you’ll notice you begin to breathe more quickly and deeply to inspire more oxygen. On a genetic level, your body increases expression of HIF1a gene, which produces Hypoxia-Inducible Factor, a protein that coordinates various physiological responses to low oxygen.
One such response is a switch in your metabolism to the anaerobic production of energy (glycolysis), because this process requires less oxygen. Nevertheless, to fuel this switch, there is a greater demand for blood glucose. These changes all culminate in an increase in basal metabolic rate: an ascent from sea level to 4,300m causing a 10-17% increase in metabolic rate.
Unsurprisingly, you might need to top up your caloric intake to accommodate the metabolic changes effected by high altitude. For winter sports athletes, studies suggest that moderate physical activity in cold temps and at high altitude requires a daily intake of 44 -55 kcal per kilogram of body weight. For more intense exercise, this figure jumps to 53-68 kcal per kg bodyweight.
Of course, your nutritional needs will vary wildly depending upon what activity you’re doing. Due to the use of lots of different muscle groups, cross-country (Nordic) skiers have the most significant energy demands. A 50-km cross-country skiing race will almost completely deplete glycogen stores. Participants therefore need to increase their carbohydrate intake before and during the event. By contrast, at less than 8.4MJ (2000kcal) per day, ski jumpers have significantly lower additional energy requirements.
Irrespective of what sport you’re doing, high-altitude can trigger still weight loss, with individuals shown to lose as much as 1.4kg bodyweight per week. Above altitudes of 3,500m, appetite may become suppressed, contributing to further weight loss. If you’re likely to spend more than a few days at high altitude, it’s especially important that you consume enough food.
With prolonged exposure to high altitude, your body responds niftily by releasing the hormone EPO to increase production of red blood cells, thereby helping delivery of oxygen around the body. This ‘polycythemic’ response requires iron to manufacture hemoglobin, the oxygen-carrying pigment of red blood cells. Eating iron-rich foods, including dark-green leafy vegetables (e.g., spinach), fish, pulses, and red meat will help you here. Iron supplements can also be of benefit - athletes consuming 105mg and 210mg iron supplements a day demonstrate improved red blood cell production at altitude.
As with the cold, it’s imperative to keep well hydrated when exercising at high altitude. The dry/low-humidity air of alpine environments serves to double the amount of water lost through breathing. Furthermore, along with appetite, your sense of thirst may diminish the higher up you get, leading you to under-consume fluids. If you’re scaling mountains this winter break, it’s recommended to take on 4-5 liters of fluid a day.
In summary, when it comes to nutrition for winter sports this holiday season: eat, drink, and be merry, but please stay in control and get home safely.