"This means that exercising, even without losing weight, can benefit individuals in terms of metabolic health," Andrea Cornford, a graduate student researcher from the University of Michigan, Ann Arbor, told Reuters Health.

"By exercising to increase their ability to burn fat and store fat as triglycerides in muscle, which is beneficial, people reduce their insulin resistance and their likelihood of developing type 2 diabetes," Cornford explained.

She presented her research last month at the 2008 American Physiological Society Intersociety Meeting: The Integrative Biology of Exercise V in Hilton Head, South Carolina.

To study the effect of exercise on fat accumulation, the researchers evaluated five obese women. In one session, the women ate a high-calorie meal and did not exercise; in another, the women ate the same meal and then exercised to expend 700 calories.

The investigators performed tests to measure the women’s levels of fatty acid oxidation, muscle triglycerides, enzyme activity and various other factors associated with fat metabolism.

They found that the women’s fat-burning rate was reduced after the session in which they overate and did not exercise. Conversely, just one 90-minute session of exercise – enough to expend the excess 700 calories that were consumed – increased the rate of fat-burning and increased the amount of fat that would be stored in muscle, Cornford reported.