Part 4: Should You "Fat Load" Before You Carbo Load?
In Part 3 of this series, Active Expert Matt Fitzgerald explained how to use sports drinks optimally. In this article, Matt discusses the importance of fat in marathoners' diets, and how this nutrient can help you race better.
Fat has a bad reputation. Most health-conscious eaters think of fat as a harmful nutrient. There aren't many advocates of high-fat diets. But high-fat diets offer one significant benefit to runners. As a general rule, the more fat you include in your diet as a runner, the more fat and less carbohydrate your muscles will burn when you run. This adaptation could increase your endurance and reduce the likelihood of your hitting the wall in long races, such as marathons because the depletion of muscle carbohydrate stores is the most common cause of hitting the wall in such events.
Studies led by Vicki Lambert at the University of Cape Town, South Africa, in the late 1990s demonstrated that significant endurance increases resulted from a period of fat loading before exhaustive exercise. Specifically, cyclists required to get roughly two-thirds of their daily calories from fat for 2 to 4 weeks lasted more than twice as long in a stationary bike ride to exhaustion that was performed at a fixed, moderate intensity. This huge boost in endurance was associated with increased fat burning and reduced glycogen (i.e. carbohydrate) burning in the muscles.
Most endurance athletes, including marathon runners, load up on carbohydrates before races. Lambert's findings may seem to suggest they should load up on fat instead. Not so fast. The problem with using a high-fat diet to increase the fat-burning capacity of the muscles is that it reduces glycogen stores in the muscles and thereby reduces performance at higher intensities. The reason is that glycogen is a much more powerful fuel than fat for high-intensity activity. Depending on how fast you run in marathons, you may need to rely on glycogen to sustain that pace and fat loading could compromise your ability to do so.