Friday, January 21, 2011

Low Carb Diet for Runners.

It sounds crazy, but there are a couple new studies saying it is best to train, at least some, without eating any carbs before and during your long runs. While this goes against everything people have said to me about running nutrition, it makes sense from my experience with low carb diets.

So it turns out doing your long runs without eating carbs can improve your running and help you lose weight.

What strikes me about this is that it seems obvious. Of course it helps if you train your body how to burn fat for fuel. The mechanism by which your body burns fat can be exercised and improved, just like your cardiovascular system can be improved. If you can train your body to improve it's efficiency in delivering oxygen to your muscles, why couldn't you improve the efficiency of pulling energy out of your fat reserves? If you only train with high glycogen levels you are only exercising one of the ways your body powers your muscles.

This isn't just speculation, there is data behind this:
Several recent studies bear this out. At the Centre of Inflammation and Metabolism in Denmark, Bente Klarlund Pedersen, M.D., DMSc, had subjects exercise one leg once daily, and the other leg twice every other day, but in a glycogen-depleted state. The total amount of training was equal for both legs, but after 10 weeks, the glycogen-denied leg increased its endurance by 90 percent.
Further, this isn't just some experimental oddity; elite athletes already train this way. For instance, "the low-carb approach has proven effective for three-time Ironman world champion Chrissie Wellington. She does selected long training sessions -- on average one every two weeks -- with minimal carb intake," and "Meb Keflezighi, the Eritrean-born American who won the 2009 New York City Marathon -- forgo carbs before and during [his] training runs." These people are not exactly lightweights or fad-diet crackpots (like me).

Can this help you lose weight?

I've always suspected the low carb diet helped me lose weight above and beyond simply reducing calories. There are a handful of studies that seem to confirm this, but some that do not. Now there is this study about the Benefits of Exercising Before Breakfast. Looking at three groups, they increased food intake. One group did not exercise, one exercised after breakfast and one exercised before breakfast. While eating the exact same caloric intake, the only group that did not gain weight was the one that exercised before breakfast.
Only the group that exercised before breakfast gained almost no weight and showed no signs of insulin resistance. They also burned the fat they were taking in more efficiently. “Our current data,” the study’s authors wrote, “indicate that exercise training in the fasted state is more effective than exercise in the carbohydrate-fed state to stimulate glucose tolerance despite a hypercaloric high-fat diet.”
I'm going to go out on a speculative limb here and relate both of these studies to low carb diets in general. Training your body to burn your fat reserves for fuel rather than a constant feed of carbs is good for you.

Read the studies: relatively small sample sets, but tight controls and a compelling outcome.