Rendering Sense Into Fat

By Arleigh Reynolds PhD, DVM

In a way it�s like re-inventing the wheel; it may seem like a futile practice, but each time we do this we refine our understanding of the machinery and how best to use it. The research featured in Donna Marlor�s article was the latest installment in this process. Like all good research it revealed some exciting new information and raised several new questions. With that in mind I thought it might be a good time to review what we know about the role of dietary fat in sled dog performance and how this information can be applied to optimize performance and minimize health risks.

Feeding high fat diets is not a new idea, in fact it was used successfully in sled dogs long before anyone thought of racing them. Since people in the North Country have been using dogs to transport themselves and their belongings they have fueled them with seal meat, salmon, and scraps from moose and caribou all of which is high in protein and high in fat. It wasn�t until dogs were removed from this traditional diet and placed on �cereal� based commercial food that the benefits of the traditional diet became apparent. While these early dry products were convenient and balanced for vitamins and minerals they were associated with stress diarrhea when dogs were worked long and or hard.

In the 1970�s David Kronfeld and Harris Dunlap published a series of papers which redefined the accepted nutritional dogma of the time and showed that high fat, high protein diets were superior to high carbohydrate diets for promoting endurance in sled dogs. This flew in the face of the new and widely accept concept of �carbohydrate loading� that had proven very effective in human marathon running. Kronfeld and Dunlap went so far as to show that dogs could maintain normal blood values during strenuous exercise on diets completely free of carbohydrates. These dogs even maintained normal concentrations of glucose, the main sugar or carbohydrate circulating in the blood. The authors did recognize; however, that the dogs fed the carbohydrate-free diet experienced occasional diarrhea while running. They concluded that a small amount of carbohydrate, about 5% of the calories, may be necessary to promote optimal gut function during hard work. Unlike the other energy nutrients (fat and protein) carbohydrates can be used with or without oxygen which is sometimes of limited availability in the gut during hard work. The lining of the gut gets its nutrients from what is in the gut and not from the blood stream so Kronfeld and Dunlap suggested that having a little carbohydrate available during hard work might keep the gut better fueled and decrease stress diarrhea. These studies were the basis for the addition of meat which is high in protein and high in fat to dry dog foods. The concept has been further developed today with the formulation of performance diets which are so high in protein and fat that they may work without the addition of meat. By the 1970�s we were back to the traditional concept of feeding a high fat high protein diet but we still didn�t know why these diets worked better and why this strategy was more successful than carbohydrate loading.
I�ve always thought it helps to understand how something works if you want to optimize its use so in the late 1980�s we started re-examining the role of diet in performance. Our first study evaluated the effect of feeding a high fat or a high carbohydrate diet on how energy was stored and utilized in sled dogs. We discovered that even in the untrained state, dogs fed a high fat diet were better able to mobilize and utilize fat as a fuel the first day they ran in harness. This was significant because at the time many mushers fed any diet that would prevent death in the off season and waited to switch to a good diet at the onset of training. It takes between 8 and 12 weeks for a dog to completely adapt to a high fat diet thus dogs fed this way were beginning their season in a real deficit.

In this study we also found that dogs fed a high fat diet were able to sustain intense exercise longer than those fed a high carbohydrate diet. At that time, and to some extent still today, the most popular endurance enhancing strategy used by human athletes was to load their muscles with as much carbohydrate (or glycogen) as possible before beginning an event. While fat can supply most of the energy necessary for low to moderate intensity exercise (up to 60% VO2 max) carbohydrate must be added in as exercise intensity increases and becomes very important for exercise intensities above 80% of VO2 max. The depletion of the relatively small carbohydrate stores forces an athlete to slow down to an exercise intensity that can be sustained predominantly by burning fat. This is what happens when an athlete �hits the wall� or �bonks� as they say in cycling. Athletes who carbohydrate load �overfill� the carbohydrate tanks in their muscle and so can run longer than those that start the race with a less full tank. This assumes that both athletes use their carbohydrates at the same rate, and that is where the dogs fed a high fat diet have a distinct advantage. Although the dogs fed a high carbohydrate diet stored significantly more carbohydrate in their muscle they also used it at twice the rate of the high fat fed dogs. We found that dogs fed a high fat diet could sustain very intense hill climbing 30-50% longer than those fed the high carbohydrate diet. Carbohydrate sparing rather than carbohydrate loading appears to be the most successful strategy for endurance in sled dogs.

From these studies we found that dogs trained on high fat diets were able to generate more power from fat than dogs fed a high carbohydrate diet. We still did not know the mechanism responsible for this amazing adaptation. To shed light upon this question we ran dogs on the treadmill while wearing a mask and measured how much oxygen they used and how much carbon dioxide they generated while exercising at gradually increasing intensities. This information told us what fuel they were using at different intensities and also defined their VO2 max. VO2 max is the maximum amount of oxygen your dog can burn per minute per unit body weight. It sets the physiological limit for performance and is often used in determining an athelete�s performance potential (bigger is better). Lance Armstrong has a VO2 max of about 82 ml/kg/min. We measured dogs on our team that had a VO2 max of 240 ml/kg/min or about 3 times that of Lance Armstrong. I always tell people that is why we ride on the sled and the dogs pull it! In these studies we found that if you took the same dogs, trained them identically and fed them a high fat diet for 12 weeks and then a high carbohydrate diet for 12 weeks they achieved a 30% higher VO2 max on the high fat diet. This is greater than the increase you usually see as you progress from the untrained to the trained state. They also achieved a significantly higher power out put from fat alone when fed the high fat diet (60% VO2 max on high fat vs 40% VO2 max on high carbohydrate). This translates into higher sustained speed over time. These results were so unexpected that we repeated the study 3 times to make sure they were real. We then examined muscle biopsies and found that dogs fed the high fat diet had re-tooled the machinery of their muscles to enable the changes we had measured. High fat fed dogs had 30% more mitochondria per fiber than high carbohydrate fed dogs. These little particles are the site in the cell where fats and carbohydrates are �burned� with oxygen and converted into the energy form used by the muscle to do work. When dogs were switched from a high fat to a high carbohydrate diet the numbers of these mitochondria decreased, VO2 max fell and max power out put from fat as a fuel decreased. Feeding a high fat diet not only provides the most important fuel for work, it changes the structure and function of the muscles so that they can use that fuel better. The bottom line from these studies performed on sprint sled dogs is that you could run further at a faster speed when you fed a high fat diet than you can when you fed a high carbohydrate diet.

Although providing adequate amounts of fat is a key to success in fueling a sled dog, carbohydrates still play an important role, and this role may differ depending upon the arena in which the dog is expected to perform. On the sprint side, exercise intensity often exceeds 85% of VO2 max. Even though fats supply most of the energy up to 60% of VO2 max, the remaining 25% or so must come from carbohydrates and if that fuel source is depleted, speed and performance will decline. The most successful strategy for maintaining carbohydrate stores over several successive days of racing is to give the dog a dose (1.5 g/kg BW) of rapidly digestible carbohydrates, like maltodextrin, immediately after exercise. The timing of the dosage will have an important bearing on the outcome. It is important that the dogs be dosed as soon after exercise as possible. There is a short window of time when the body will funnel the carbohydrates given towards replacing muscle stores. That window shuts about 30 minutes after exercise ends. Also, carbohydrate administration can adversely affect fat metabolism and it takes a while for the body to store the carbohydrates so they should only be given when there is at least 4 hours of rest following their administration. This strategy has been used successfully for over 15 years in sprint racing, but does it work in mid distance and long distance racing?

Anytime when carbohydrate utilization limits performance this strategy will be important for success. In mid distance racing, where speeds may average 10-12 mph, or in races with repetitive hill climbing, there will be enough exercise above 60% of VO2 max to warrant carbohydrate replenishment. In long distance racing exercise intensity rarely exceeds 60% of VO2 max. This intensity is not sustainable over the time period that these athletes perform and so there is still some question as to the necessity of carbohydrate replenishment in this side of the sport. A step towards the answer comes from some recent and interesting work out of Oklahoma State University. This group showed that dogs exercising for about 100 miles per day for 4-5 days showed an initial drop in carbohydrate stores to as low as 20%of the pre-exercise value and increased over time to settle back at about 55% of the initial value. These levels are probably enough to support sustained efforts at the 6-8 mph pace most teams maintain at the end of long distance races. The question is, if two mushers found themselves in White Mountain within a few minutes of each other, would having increased carbohydrate stores at this stage of the race, which is attainable in an 8 hour rest period, yield a speed advantage in the 70 mile trip to Nome? Could they go 10-12 mph over that distance if they had the carbohydrate reserves to do it? The amount of carbohydrates necessary to replenish these stores would not significantly alter total calorie or fat intake but if applied at a strategic point in the race might have an influence on the outcome. Some one should do a study.

If high fat diets optimize performance in sled dogs, the next questions should be how much fat and what type should be fed. Here we get into the practical side of nutrition, the side which is a blend of art and science. The definition of a high fat diet will vary depending on who you talk to and the animal involved. Sled dogs have an innate tolerance for dietary fat levels that would literally kill other breeds of dogs. For many of the sporting breeds a high fat diet would be considered 30% of the total caloric intake. For sled dog purposes high fat diets generally range from 50-80% of the calories. From experience I can say that 50-60% of the calories in fat is safe to feed long term during training as long as the rest of the diet is balanced for protein, vitamins and minerals. Once you exceed 60% of the calories you must be careful because at this point fat starts to displace other nutrients, most notably protein, and you can run into serious problems if you feed these ultra high fat diets long term. The best example of this I can remember was a call I got from a prominent musher in Skwenta when he scratched because his team was too flat to continue. For those of you who know your Iditarod geography Skwenta is much closer to Anchorage than to Nome, so I was surprised that one of the mushers picked to be a front runner was already done. When he had a vet examine his dogs he found they were all profoundly anemic. An evaluation of his diet, which he had been using for several months, showed that he was feeding almost 85% fat. I had him drop the fat to 55% of the calories, increase the protein to 35% of the calories and in 2 weeks their blood counts had all returned to normal. The next year with same team on this new diet he finished 6th in the Iditarod. I have seen this same scenario many times and feel certain that for long term feeding you are playing with fire if you exceed 60% of the calories as fat. You can go as high as 80% of the calories for up to 2 weeks without a problem if the dogs are working hard, previously adapted to a high fat diet, and they start the period in good physical condition. You may suspect a problem is starting to arise if the dogs� performance flattens out, they go off food, or they become anemic.

There are many great sources of fat but no one source can provide all of the possible benefits fats have to offer so I usually blend 2 or more fats when I feed my dogs. Some fat sources are extremely expensive, some impractical and some unsafe, so you want to know what and why you are mixing specific ingredients before you start. Moderation is the key. Too much beef tallow and you may end up with hot spots in their skin. Too much vegetable fat and you may not get enough benefit from your fish oil. Don�t even bother with fad fats like coconut oil and flax oil. Coconut oil is too stiff at cold temperatures to be practical and I have yet to find a dog that will voluntarily eat it. Flax oil is often touted as a good omega-3 source but the omega-3�s in flax oil are not in a form that dogs can incorporate in their body and so they become a very expensive substitute for vegetable oil. I like to mix one part animal fat, one part vegetable fat, and one part fish oil. For my animal fats I prefer beef tallow or poultry fat. They are palatable and stable and not too expensive. For vegetable fats, if money were no object, I would love to use wheat germ oil but since it is, I use corn, canola, or safflower oil depending upon availability. Vegetable oil provides essential fatty acids (EFA�s)which are necessary for healthy skin and coat and provide a waterproof barrier in the skin. These EFA�s are very important in maintaining healthy skin on the foot. I live in Alaska so salmon oil is fish oil of choice but herring oil and menhaden oil will also work well. Make sure your fish oil is cold pressed, and well preserved with some real preservative like ethoxyquin, BHA, or BHT. Rosemary and Vitamin E are popular natural preservatives but they don�t have the staying power of the artificial preservatives. Store it away from light, heat, and air. Fish oil that has gone rancid can stop your team�s progress faster than a charging moose. I have seen several mushers season�s ended by this problem. The common complaint is that the dogs start out fine but fade after just a few miles usually exhibiting a stiff gait and inability to stretch out. The problem can be resolved by removing the offending fish oil and supplementing with large doses of antioxidants during a period of enforced rest. Fish oil can be great for decreasing inflammation, improving coat quality and even enhancing oxygen transport but make certain you have a safe source and feed it with moderation (never more than 1/3 of the fat calories) and with antioxidants (400IU Vitamin E or 2-4 mg astaxanthin).

And so we have re-invented and refined the high fat diet �wheel� one more time. As someone who has spent their entire professional career studying the relationship between diet and performance in sled dogs, it seems humorously ironic to me that if we put together all we have learned from these many studies we would formulate a diet very much like that which was fed a thousand years ago.