The Claim: Doing cardiovascular exercise on an empty stomach burns more fat.

By ANAHAD O'CONNOR

THE FACTS

Working out while hungry may fly in the face of conventional wisdom, but many athletes and gym-goers push themselves on empty stomachs in the belief they'll burn more fat.

The idea, advocated in popular fitness books over the past decade, is that exercising on an empty stomach forces the body to dip into fat stores for fuel instead of the carbohydrates quickly available from a pre-workout meal or snack. But while it seems to make sense, research shows that exercising in this way doesn't offer any benefit and may even work against you.

After reviewing years of research on the subject, a report published this year in Strength and Conditioning Journal concluded that the body burns roughly the same amount of fat regardless of whether you eat before a workout. But you're likely to lose muscle by exercising in a depleted state, the report found, and without fuel to aid the workout, exercise intensity and overall calorie burn will be reduced.

One of the studies reviewed in that report looked at cyclists when they trained after eating and when they trained while fasting. When they trained with nothing in their stomachs, about 10 percent of the calories they burned came from protein, including lost muscle, the researchers wrote.

In a separate study published in 2002, scientists found an additional benefit from a pre-workout meal: Healthy women who consumed 45 grams of carbohydrates before their workouts ended up eating less throughout the remainder of the day.

THE BOTTOM LINE

Exercising on an empty stomach does not help burn more fat.

This is a more complete version of the story than the one that appeared in print.