Wednesday, September 25, 2013

The Sled Dog Diet: Fueling a Unique Athlete

This summer, while teaching a freshman, introductory course on sport science, the class and I discussed the nutritional requirements for various types of activities and sports. We talked about the energy demands of different sports and how diets should be individualized to meet specific demands and replenish energy stores. As is usually the case, the issue of extreme, endurance athletes came up. As we talked about marathoners and Tour de France cyclists, I asked the class to consider a group of athletes who compete in a very unique and extreme endurance event – dog sledding. How much work are sled dogs asked to perform each day? What sort of diet must they eat? Understanding the sled dog’s daily energy demands and considering what types of foods are needed to fuel their engines helps give insight into how important diet is to elite performance.

Sled dogs are an incredible group of athletes. These animals are trained to compete in multi-day endurance events such as the Iditarod race. The Iditarod is annual race from Anchorage to Nome, AK. a distance of more than 1100 miles. Unlike the Tour de France, this race is continuous. That is, it is not run in stages. Rather, the starting gun is fired and the teams decide for themselves when to race and when to stop for rest and food. Top teams typically complete the distance in 9-10 days. Also, unlike similar cycling events such the Race Across America (3000 miles completed in ~10 days), sled dogs don’t have the ability to eat and drink while exercising.

Over the course of the race, sled dogs in the Iditarod may run between 100 and 150 miles per day, often running at a pace of 5-6 minutes per mile. To make matters more difficult, this race is run in sub-freezing temperatures, across hilly terrain, often during snowstorms. These athletes are not large. Sled dogs weigh between 45 to 55 pounds (20–25 kg). While Huskies and Malamutes are used, most are mixed-breed or mongrel dogs. They are however, bread for combinations of speed, power and endurance. As a result of breading and training, maximal oxygen consumption values approach 250 ml O2/kg/min. By comparison, an elite cyclist may have a VO2max between 70 and 80.

As one would guess, the amount of energy these dogs expend during a 100-150 mile run is considerable. On a given race day, they use between 10,000 and 13,000 kcal or calories. Based on body weight, that equates to a 165lb soccer player (75 kg) expending nearly 40,000 kcal. Or about 8-10 times what he actually uses each day during a competitive season.

The energy expended by these dogs must be replaced through their diet. Thus, each dog needs to take in ~12,000 calories per day. One critical issue that mushers face is the amount and composition of the food given to their dogs. Based on what we know about glycogen depletion and replenishment following endurance exercise, one would assume that a high carbohydrate would be best for these endurance athletes. However, if we do a few simple calculations, we see a problem emerge. Assume that carbohydrates and proteins contain 4 kcal per gram of food and fats contain 9 kcal per gram, a 12,000 kcal diet containing 65% carbohydrates, 20% fat and 15% protein would require 5.9 lbs (2.7 kg) of food on a daily basis. Remember, these are 50 lb dogs. Using the 165 lb player as a human comparison, that would equal nearly 20 lbs of food.

On way to address this is to use a more “calorie-dense” diet, one that contains more calories per gram. For these dogs, they eat a diet that is about 60% fat and 20% carbohydrates. Typical foods are poultry, beef and oily fish like salmon, sometimes supplemented with vegetable and animal oils and fats. Vitamins, minerals and probiotics are also added to the mix. This percentage of fats, carbohydrates and proteins reduces the amount of food needed to 4.4 lbs (2 kg). Still a tremendous amount of food, but more manageable. Also, dogs are fed every few hours rather than in one or two very large meals.

Fortunately, dogs compete very well on a high fat diet. Most working dog breeds actually perform better when placed on a high fat diet. While dogs store more muscle glycogen on a high carbohydrate diet, the high fat diet helps them use fats as an energy source more effectively. The result is, muscle glycogen is spared and performance is maintained during the race. This is not the case with humans. We do not perform well on a high fat diet and quickly suffer glycogen depletion and exhaustion. Also, horses can develop severe gastrointestinal problems on diets that contain more than ~12-14% fat. So, the diet of a competing sled dog is specifically designed to meet their energy needs and their metabolism

What can soccer players learn from sled dogs? First, it is important to match the diet to the energy demands of the sport. The number of calories taken in should match the amount expended. During pre-season, when teams may train twice per day, energy expenditure can be high. As discussed in previous articles, many players do not eat enough calories to match what was spent during training. Yet the intake of calories must match expenditure.

Second, choose specific foods wisely to maximize energy replenishment. Since sled dogs have a very high caloric need and they perform very well on a high fat diet. Thus, their diet is constructed to meet a specific need and to take advantage of their unique metabolism. Players should do the same. Whether facing a single match or a week of heavy training, the specific foods selected, the amount of food eaten, the timing of meals and individual preferences should all be considered when developing a diet strategy. In this case, carbohydrates are the most plentiful part of the diet.

By keeping these concepts in mind, players should be able to navigate the nutritional challenges of training and competing. Planning and preparing a diet that meets their individual needs will go a long way in improving their performance on the field.

More Information

For more information on the soccer diet, Robin Russell and I have developed and on-line course and community – Soccer Diet: The Simplest Way to Improve Your Team’s Performance”. Also, copies of The SCIENCE Behind Soccer Nutrition are available for outlets such as Amazon.