People who cut back on carbohydrates will burn more calories than those who cut back on fat, according to a new study published Wednesday in the Journal of the American Medical Association.

Researches wanted to find the best way for individuals who'd lost weight to keep the pounds off.

Scientists had 21 obese participants, ages 18 to 40, lose about 30 pounds. each participant then followed one of three diets prepared for them for four weeks and underwent routine metabolic tests.

Participants burned about 300 calories more a day on a low-carb diet than they did on a low-fat diet.

"That's the amount you'd burn off in an hour of moderate intensity physical activity without lifting a finger," said the study's senior author David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital.

He added that the reason for the low-carb advantage is still unclear.

But experts warn that a diet too low in carbohydrates and too high in fat can lead to heart problems. Some recommend a more balanced approached by eating carbs based on whole grains.

Whether low-carbs or low-fat, one nutritionist summed up the secret to dieting this way : "If you want to lose weight, eat less."