Climbing is a long and demanding endeavor, with a typical summit day on Rainier or Denali stretching for twelve to fifteen hours. Every time you take a step, your muscles require energy in the form of ATP to be able to fire. ATP is created within the muscle cells by mitochondria from two main nutrients: carbohydrates and fat.

For many years, athletes have focused on their carbohydrate intake as the key to performance. Carbohydrates provide a readily accessible and easily digestible energy source for your body, which is the reason that they are the main content in most sports foods; just look at the labels of shot blocks, Gu’s, bars, energy drinks, and the like, and you will see a heavy focus on sugar. There is a good reason for this: your body has a limited ability to digest food while exercising (digestion requires energy of its own), and carbohydrates and sugars are the easiest to digest, requiring little to be done to the glucose components before they enter the bloodstream and are carried to the cells.

The main issue with a reliance on carbohydrates is that your body has the ability to store a finite supply of glucose in the muscle cells and the liver in the form of glycogen. For trained athletes that are efficient with their energy usage, that store still only lasts for about 2 hours of sustained hard effort. If you aren’t familiar with the term “bonking,” it’s that feeling when your performance drops off a cliff; you don’t feel like you are working that hard aerobically, but you can’t possibly go any faster or harder. You’ve run through those glycogen stores and your muscles are out of fuel. Eating while you exercise can help to delay bonking, but your body can only process about 250 Kcal of sugar per hour, far less than you expend over the same period. Even though we are replenishing our sugar fuel, we dip further and further into those reserves as summit day goes on. At the same time, even the leanest among us carries over 24 hours of energy in the form of fat stores. Wouldn’t it be nice to recruit those stores while you are climbing?

Fatty acids are the most energy dense nutrients in our diet and our body stores them readily. They create more ATP per unit than sugars, and our body’s ability to store them can leave us with a huge reserve energy supply. The problem is that when fatty acids and sugars are both present, our metabolisms preference burning the sugars for energy. Julia Goedecke is a sports scientist who has been examining the influence of fat oxidation (metabolism) in endurance athletes. In examining rates of fat oxidation in athletes at different intensity levels, she found a vast difference in overall rates of fat oxidation. Some burned nearly no fat at rest, while others metabolized nearly 100% fat at rest, but while there were differences in overall rates of fat metabolism, those who metabolized more fat at rest derived more of their energy from fat at all intensity levels too. This would suggest that if we can train our metabolism to derive a greater percentage of our energy from fat, it will continue to do that as we up our intensity climbing, and we will use our sugar reserves more slowly, and hopefully avoid the dreaded “bonk!”

Now that we’ve introduced the idea of developing your fat metabolism, stay tuned next week as we get into the details about how to accomplish it.

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For more reading Alan Couzens has a number of interesting blogs on the subject. A good one to start with is Improving Fat Oxidation.

Questions? Comments? Do you have experience applying LCHF nutrition to endurance sports? Share your thoughts here on the RMI Blog!