The Case for Carb Loading

A new study backs the time-honored tradition of carb loading before races.
A new study backs the time-honored tradition of carb loading before races. Ira Leoni / Getty Images

Recently, some coaches, trainers, and athletes have denounced the pre-race pasta dinner, saying that carb-loading before endurance competitions isn't the most efficient practice. Instead, they argue for low-carb, high-fat meals, sometimes called the Keto Diet. The plan purports that by drastically cutting carbs, you can trick your body to burn through fat, which, they claim, is a better fuel. The theory is controversial to say the least, and may become all the more fringe thanks to a new study that found that carbs, not fat, contribute up to 91 percent of the energy used by runners, no matter what kind of diet they're following.

Researchers from the Centre for Exercise and Nutrition at Australian Catholic University who've been studying the carb question for the past few years, recruited competitive half-marathon runners to test carbs versus fat as a fuel source. They fed these men either carb-heavy or carb-free meals before, during, and after they ran 13.1 miles at a slightly slower pace than their best half-marathon times. Using a technique never before used in a trial on runners, they gave these guys nicotinic acid along with their food, which blocks the body's ability to tap fat stores for energy.


The researchers discovered that, regardless of what the runners had eaten, carbs contributed up to 91 percent of the total energy they used. In other words, withholding carbohydrates didn't make them dip into fat for fuel instead. It also didn't affect their performance. They say this adds another layer of proof that for long, high-intensity runs, the body wants to and will use glycogen.

"The body needs to be able to utilize carbohydrates for performance, which requires athletes to train with high carbohydrate availability," says study co-author Jill Leckey. If athletes do not have adequate stores of muscle glycogen prior to an event, the fuel available for use is diminished. "If the body has to depend on fat stores, the ability to perform high-intensity effort is impaired," she adds.

Leckey says the precise amount of carbohydrates you need during training varies from athlete to athlete. "Carbohydrate requirements differ due to body mass, intensities, and duration of training bouts, and the timing of exercise around meals," she explains. "Just like professional distance runners, nonprofessional athletes should alter their intake depending on the amount of training they are doing. If the training demand increases, the demand for carbohydrate also increases."

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