Carbohydrates, not fats, are the main source of energy for long distance runners, a new study says.

The research from Australia included men who were competitive half-marathoners. They ran on a treadmill at 95 percent of their best half-marathon time until they were exhausted. The men ate before they ran, and were given nicotinic acid during the run to prevent their bodies from using fat stores.

Blocking the body's access to fat didn't affect how long the participants could run on the treadmill before they became exhausted, the researchers found. They also noted that a lack of access to fat didn't affect the body's use of carbohydrates, which contributed up to 91 percent of the total energy used by the runners.

The study was published recently in the Journal of Applied Physiology.

The findings show that muscles prefer carbohydrates as their fuel source during high-intensity, long-duration runs, according to study author Jill Leckey of the Mary MacKillop Institute of Health Research at Australian Catholic University in Melbourne.

"Competitive runners should focus on dietary strategies that will increase carbohydrate availability before and during competition to optimize race performance in events lasting up to 90 minutes in duration," Leckey said in a journal news release.

This study focused on competitive runners, but the results can also apply to recreational runners, the researchers said.

"It's the relative exercise intensity, for instance, the percentage of an individual's maximal oxygen uptake or maximum heart rate, that determines the proportion of carbohydrate and fat fuels used by the exercising muscles, not simply the pace they are running," Leckey said.