A recent article published in the prestigious journal Science by Dr. Louise Burke, a renowned sports scientist and nutrition expert laid out some of the latest and greatest research on optimal fueling habits for athletes. Titled “Swifter, higher, stronger: What’s on the menu?”, the authors dive into the science behind macronutrient and overall dietary requirements for optimizing athletic performance.
One of the recurring areas of confusion, challenge, and controversy that I see so often in the world of endurance athletes is the fear of carbohydrates and calories in general (although my thoughts on the latter deserve their own blog post). There continues to be rampant “carbophobia” within the athletic community that is a result of decades of misinterpretation and pseudoscience that gets perpetuated and recycled in the blogosphere and eventually buries itself within the culture. I’ve found this particularly fascinating, because throughout my entire undergraduate coursework in physiology and now my graduate coursework in nutrition, there’s very little debate on the subject of the utility and physiological function of carbohydrates. For more science on carbohydrates, tune into a podcast I did on the topic.
This confusion is unfortunate, because the fear of one of the primary and incredibly important macronutrients leads to strange and negative eating habits that can ultimately undermine performance. This cycle is hard to break out of. I’ve been there myself. But when we look through the mighty lens of science, we can wade through the murky waters of nutrition like Frodo and the Light of Earendil and find the light in dark places.
This brings us back to the article by Burke. If you’re interested in hearing my thoughts on this subject, I did a more in-depth analysis on the article on my podcast, Thought For Food. In this post, I simply want to share a couple of key takeaways and thoughts on this article that should offer some insight into the importance of carbohydrates for athletes.
Glycogen, the storage form of carbohydrates found in our muscles and liver, is an essential and readily available fuel source for working muscles and basic functioning of the body. Resting glycogen concentrations are higher in athletes than sedentary humans, pointing to the body’s adaptation to utilizing this source of energy. Oxidization of glycogen/carbohydrate yields about 5% more energy than fat.
There’s strong evidence that consuming carbohydrates during exercise improves performance by maintaining blood sugar through sparing liver glucose production. Athletes should aim to eat around 30-60g of carbohydrate per hour during endurance activity. However, intestinal carbohydrate absorption is likely the rate limiting factor in oxidizing carbohydrate during exercise, which is why it’s critical to train the gut to maximize the absorption rate of different types of carbohydrates.
What about fat? Although there is a lot of discussion about the utility of “fat adaptation” and the truth that even very lean endurance athletes have significant fat stores, there doesn’t seem to exist a mechanism for closely regulating the availability of using fatty acids as the primary fuel source during exercise. From Burke: “To date, it appears that protocols that substantially increase fat oxidation also decrease metabolic flexibility by reducing CHO substrate pools and/or the ability to rapidly oxidize them. The bottom line is that when elite athletes train for and compete in most sporting events, CHO fuels are the predominant and critical substrate for the working muscles, and the availability of CHO, rather than fat, wins gold medals.” Despite claims that low carb or keto diets have unlimited fuel from fat for exercise, decades of empirical evidence and recent interventions show that the oxidation of carbohydrates yields more ATP per unit of oxygen than fat. So, strategies for athletes in long and intense exercise may involve training the gut to use multiple sources of CHO, maximizing glycogen stores, etc. At the same time, training increases the metabolic flexibility of the muscles to switch between carbohydrate and fat to more effectively meet the demands of exercise.
To summarize a primary theme of this paper: carbohydrates are a critical component to the athlete’s diet. They are not something to be fearful of, unless of course we are relying heavily on processed and refined carbohydrates as mainstays of our diet. A sweet potato is not sweet tea. As athletes, we can fuel our machines with foods like fruits, grains, starches, and at certain times, refined carbohydrate sources to get through heavy periods of training and competition. Carbohydrate literally powers our muscles and our brain, and without it we can’t reach the potential for performance. How do you think Frodo made it to Mordor?
Of course, we also need the other two macronutrients, protein and fat, which serve their own important functions. By eating a diet rich in a variety of whole foods to fuel the demands of our sport, we will meet the requirements for these nutrients quite easily.
Let’s change our narrative about food from “will this make me fat?” to “will this make me powerful?”.
Burke LM, Hawley JA. Swifter, higher, stronger: What’s on the menu? Science. 2018; 362(6416), 781-787.