Carb-Loading and Exercise: A Healthy Combination?

When it comes to enhancing performance, filling up with carbs may not be as beneficial as some think. Here's why.

On low-fat and low-calorie diets, people can do serious harm to themselves by overexercising. When the body isn't getting enough protein from food, it turns to its only source of nondietary protein: muscle. The body will actually begin to consume its own healthy muscle tissue. If you think this happens only to starving people in developing countries, you're wrong. Do you know someone who eats half a bagel and fruit for breakfast and a salad and diet soda for lunch? And then goes to the gym right after work? Where is her body going to find the protein to fuel her for those 45 minutes on the stair-climbing machine? It will turn to the very muscles she's trying to build and tone--not to the fat cells she thinks she's burning.

Another benefit of a controlled carb nutrition program is that your metabolism won't go into starvation mode when you start exercising. Consider this: When you restrict calories and increase exercise, your body reacts just as it would when we were cavemen. As far as your body knows, it thinks there's a famine going on out there and—by unfortunate coincidence—some bear must be chasing you at the same time. Your body goes into survival mode and wisely sends out an all-systems alert to conserve resources. It literally turns your metabolism down a notch.

If you instead give your body all the protein and fat it desires, your body will know that food is plentiful. It will then accept your running, walking, stair climbing or bicycling and leave your metabolism to hum along, and maybe even step up its pace.

The Myth of Carb-Loading
You've probably heard of marathoners and other elite athletes inhaling gargantuan amounts of pasta before big endurance events, often referred to as carb-loading. It turns out that fat-loading may be more effective. More scientific research is required, however, studies on both animals and humans have suggested that a fat-rich diet may increase endurance. A 1994 study compared the effects of a high-carb/low-fat diet and a high-fat/low-carb diet on two groups of trained cyclists. During high-intensity exercise, the groups performed equally well; during prolonged, moderate-intensity exercise, endurance was significantly enhanced among the cyclists on the high-fat/low-carb regimen1. Two other studies on humans suggest that increasing dietary fat from 15 percent to 42 percent of total intake increases maximum oxygen consumption and endurance capacity2-3. The published research suggests that increases in dietary fat may be beneficial—not only for general health, but also for physical endurance.

Selected References