High-Carb vs Low-Carb Diet: Which Is Better for Athletes?

Laird Harrison


December 04, 2015

In This Article

Should Diet Guidelines Be Revised?

Patrick Davitt, PhD, tries to keep carbohydrates down to 20% of the calories he consumes. You might think he's following one of the weight-loss regimens that became so popular a few years ago.

But Davitt already is slender and fit. In fact, he likes to run marathons, which puts his diet choice squarely in opposition to the recommendation of the American College of Sports Medicine (ACSM) that athletes start with the standard US Department of Agriculture guidelines of 45%-65% of energy from carbohydrates—then add more carbohydrates the more they exercise.[1,2]

An assistant professor of exercise science at Mercy College in Dobbs Ferry, New York, Dr Davitt argues that the official guidelines, which are now being revised, should describe the benefits of diets like his. "This should be provided as an option to athletes," he says.

The position has gained some recent traction as more and more studies show that the human body, once adapted to a low-carbohydrate diet, can fuel feats of endurance with energy stored in its own fat.

Dr Davitt presented one such study in May at the ACSM annual meeting.[3] He and his colleagues found that runners who adapt to a low-carbohydrate diet can burn up to 1.54 g of fat per minute, 50% more than the highest previous estimate. The athletes in this study had all run 50-mile races, and the study suggested that these athletes don't need energy bars and sports drinks.

High-Carb Advocates Aren't Convinced

But the low-carb advocates still haven't rooted out the sports world's deep commitment to carbohydrates. The ACSM's 2014 textbook for personal trainers suggests these menu options for a healthy breakfast when traveling: "Order pancakes, French toast, muffins, toast, cereal, fruit, and juices."[4]

Such recommendations are derived from research showing that people quickly burn up the glycogen in their muscles when they exercise, then use glucose in their blood. Without replacing that glucose, the thinking goes, an athlete will quickly run out of energy. And the human body can very quickly convert dietary carbohydrates to glucose.

"A single 30-second bout of high-intensity activity could reduce muscle carbohydrate (glycogen) storage by more than 25%," warns the personal trainer textbook. "By consuming a high-carbohydrate diet and carbohydrate-containing sports beverages, a client can improve energy reserves and enhance performances of repeated bouts of high-intensity activity."[4]

As a result, the American Dietetic Association, Dietitians of Canada, and the ACSM, in a position statement on nutrition and athletic performance, recommend 6-8 g of carbohydrates per kg of body weight per day, "depending on the athlete's total daily expenditure, type of sport performed, sex of the athlete, and environmental conditions." For a 150-pound person, that's roughly the equivalent of 10 slices of bread.[1]

It's no wonder that cross-country teams wolf down big pasta dinners the night before a meet or that empty sports drink bottles pile up on the sidelines of soccer games.


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