Between What You Didn’t Know and I Didn’t Know, We Came Out Even

And we were both disappointed.

When I reviewed the two graphs from the study by Reynolds and Taylor, that comment from the movie Spirit of the Wind came to mind. George Attla and his trapping partner Moses traded dogs sight unseen. One dog turned out to be blind and the other  had only three legs.

What is the take away from the study? VO2 max does not mean much and  has very little predictive value for practical running endurance or performance when applied to individuals or groups. VO2 max is a well-defined quantity that can be measured relatively accurately and easily. Unfortunately as the results of this study show, it does not correlate to endurance or running performance over distance. No one should expect that the Labrador retrievers on the high fat diet can run a 20 km race competitive with the better trained sled dogs, even though the VO2 max values are similar in both groups.

What were the diet variables? Was the protein content the same for all diets? What would the Labradors’ V02 values be if they also trained the same as the sled dogs? That would make the study more interesting. My understanding was that the study resulted from Richard Taylor’s challenge to Reynolds based on Taylor’s understanding of comparative physiology for many different species and his observations that between species the aerobic capacity was linked to endurance performance and fat metabolism and adaptation… echoing David Kronfeld’s earlier work with dogs.

Running coach Jack Daniels’ Vdot recognizes the limitations of VO2 max. Vdot is derived from measured running times over shorter distances that the athlete has trained for, and predicts the best performance that could be expected if the same athlete trained for longer distances properly-as illustrated and defined in Jack Daniel’s book, Running Formula.

Performance is determined by three variables or factors, and training can improve all three, but most practical training methods use a series or cycle of workouts and schedules that target the three separately. The three are: speed (which is somewhat reflected by VO2 max,) endurance, and recovery/recuperation. When you focus on speed you typically reduce the endurance; when your training focuses on endurance you typically reduce the speed; so the balance of training speed vs. endurance determines the overall results.

Fast And Faster

Discussion about fasting with many people often ends with the complaint, “I can’t do that, I have hypoglycemia.”

Does a  person wake up in the morning with hypoglycemia? Not! Is my impression. What is hypoglycemia except the consequence of self-inflicted hyperglycemia? The typical course of events is eating too much sugar-containing and/or sugar-generating  food followed by insulin spike which in turn causes hypoglycemia and then stress hormone-related catabolism when tissue protein is destroyed to generate sugar and “ketones” for energy pre-empting fat stores which would otherwise be sufficient and available in the absence of glucagon and cortisol triggered by stress. Obesity and diabetes often go together.

But if a person wakes up each morning convinced that he or she suffers from hypoglycemia without recognizing that it is a result of hyperglycemia then it becomes a typical positive feedback loop. Eating candy bars or other sweets every one or two hours to prevent hypoglycemia only establishes the problem or dependence on sugar more severely. It’s the cause of diabetes not the result.

Coffee and other forms of hard caffeine drinkers have a similar problem and rationale. They claim they feel so good when they drink a cuppa but according to recent studies it is only the relief of withdrawal symptoms. So my grandmother (who did live to 102 years) was a caffeine addict, sometimes needing a cup of coffee in the middle of the night to get back to sleep.

A more useful tangent for dog mushers is the subject of calorie restriction and other dietary modifications to improve performance or accomplish whatever particular physiological object you have in mind, such as weight loss, weight gain, longevity, fitness, endurance.

Who had the best breakfast?

Sometimes the best breakfast is no breakfast…

Diet means not only the composition of the food but, just as important, the timing and context in which it is fed, the form in which it is eaten, all factors that determine overall results and success.

After reading a lot of confusing studies (confusing because the conditions and controls limited the generality and application to other situations) and seeing the harmful results of many forms of carbohydrate loading, hyperglycemic food, and other diet fads, I came to a hypothesis more than twenty years ago when I was training my dogs for stage races and training myself for triathlons.

Caloric restriction may include limiting the total food intake or can also include longer time between meals. One factor could be the caloric interval between meals. How long does the animal go after the carbs have been digested before another meal. How long does the animal use stored fat instead of recently ingested carbs as the primary energy source? Training fat metabolism has a lot to do with endurance performance.

So, another related factor could be the amount and period of time between carbohydrate feeding. Research done by Arleigh Reynolds and Richard Taylor with sled dogs and Labradors showed favorable effects from high fat diets: increased mitochondrial density in muscle cells and increased VO2 max.

Another way of looking at it: when protein is constant percentage of dietary calories the more important contributing or distinguishing variable could be lowered carbohydrate, not higher fat. These effects are comparable to those from exercise and training; though they can’t completely replace physical conditioning they can partly substitute and complement exercise, especially in hot/summer weather when prolonged exercise would be difficult. VO2 max is a surrogate not valid for endurance… see Jack Daniels book Running Formula for a good discussion of his proxy  Vdot and its relevance as a predictor of performance over a wide range of distances.

I think there is an optimum meal size for dogs depending on their activity level and the food composition. Any moderately active dog feed an adequate diet can easily go two days between meals. What is normal for wild canine species, wolves? Probably more than two days. There is also evidence and the belief among working dog trainers going back hundreds of years that dogs perform better on an empty stomach.

An article in the magazine Sports Nutrition Insider ( for gratis? subscription) describes how recent research has discredited many assumptions about sports performance related to nutrition.

“Numerous studies, for example, have shown that the involuntary performance decline associated with fatigue begins with a reduction in output from the motor cortex to the working muscles that precedes glycogen depletion, acidosis, or any other peripheral factor that would cause the muscles to fail locally.”

In other words, the tail does not wag the dog, the brain wags the tail, or not.

How is fatigue or endurance mediated by the brain and nutrition? Examples of research results illustrating answers to that question are given in the article.

“Caffeine does not increase fat oxidation… but instead blocks adenosine receptors in the brain, increasing noradrenaline and dopamine, and thereby reduces perceived exertion… Older models of exercise performance… could offer no explanation as to why a drug that merely reduced how hard exercise feels would enhance performance, but it appears that this is exactly how caffeine works.”

In a study of bicycling performance it was found that cyclists rinsing their mouths with a carb sports drink every seven to eight minutes without swallowing completed a time trial two minutes faster than those who rinsed and spit out water alone. “If fatigue is the result of local dysfunction in the muscles, how could the stimulation of carbohydrate receptors in the tongue delay fatigue?”

Referring to other studies: “Drinking to completely offset sweat losses offers no performance advantage or thermoregulatory benefit compared to drinking by thirst, while increasing the risk of GI distress.”

Or hyponatremia, dilution of blood sodium to a dangerous level. In moderate temperatures this seems to be supported by experience with and for exercising dogs. But in cold weather there is also evidence that thirst is blunted in dogs and humans, reducing voluntary drinking to performance-limiting quantities. In any circumstance it does make sense to be cautious in baiting water to encourage dogs to drink more than they would otherwise.

“It’s an exciting time in exercise science… before it’s all said and done, some of this research will lead to substantial changes in how endurance athletes fuel their performance.”

Many years ago when I started giving my sled dogs snacks during races and training, when positive results were evident before the water or food could have been absorbed or metabolized, I came to realize that there was more involved than simply supplementing hydration or nutritional energy.

Richard Taylor Arleigh Reynolds slide for VO2 max

If you came this far, here is a bonus on a different subject:

Pistachio consumption may promote a beneficial gut environment

First-of-its-kind research presented as an abstract at the 2012 American Society for Nutrition suggests eating pistachios may positively impact bacterial profile of the digestive tract

After controlling for age, dietary factors and other relevant variables, the researchers observed that after 19 days, people who ate up to 3 ounces of pistachios (about 147 nuts or 2 servings) per day had increased changes in levels of various gut bacteria. According to the abstract, people who ate pistachios showed an increase in potentially beneficial butyrate-producing bacteria. Butyrate has been shown to be a preferred energy source for colonic epithelial cells and is thought to play an important role in maintaining colonic health in humans(2). The difference in gut microbes was stronger in people who ate pistachios rather than almonds. The researchers used “modern high throughput sequencing” to quantify specific gut bacterial DNA signatures before and after nut consumption. According to the researchers, this is the first study using this method to observe that pistachios and almonds may have the ability to help change the amounts of bacteria thriving in the gut.