Body Burns Some Fats
Better After Exercise
Excerpt By Anne Harding, Reuter's Health

NEW YORK (Reuters Health) - A workout can help burn the fat you eat, and keep it from adhering to your hips, even hours after you've left the gym, the results of a small new study suggest.

But this doesn't work for every type of fat, the researchers found; while previous exercise helped people burn monounsaturated fat from a subsequent meal, it had no effect on how the body used saturated fat. Monounsaturated fat is found in plant foods like olive oil, while saturated fats come mainly from animal foods.

The study "again demonstrates that all fats aren't created equal, and there are differences in metabolism and, from other studies, health outcomes," Dr. Dale Schoeller of the University of Wisconsin-Madison's Department of Nutritional Sciences, one of the study's authors, told Reuters Health. The findings are published in the latest issue of Medicine & Science in Sports & Exercise.

To investigate whether people might process fat from a meal differently after they had exercised, Schoeller and his colleagues conducted a study of seven healthy, moderately active women whose average age was 26. The women each underwent three different 2-day tests. In one, women stuck to scheduled sleep and meal times. In the second and third visits, the sleep and meal schedules were the same, but the women exercised lightly or heavily on a special stationary bike for 2 hours. They were also given a snack the night before to compensate for the calories used when they exercised the following day.

A half hour after they finished exercising or resting, at 10:30 AM, the women were given meals containing oleate, a monounsaturated fat, and palmitate, a saturated fat. Then the researchers collected breath samples hourly up until 10 PM to measure how the women's bodies were using the fat.

After the heavy exercise, the women oxidized, or burned, significantly more oleate than after light exercise or rest. And a light workout burned more oleate after a meal than resting did. But metabolism of the saturated fat was the same whether or not the women exercised.

When fat is burned, it doesn't have the chance to be stored in the body as excess fat tissue. Studies in animals, Schoeller noted, have shown that the body uses monounsaturated fats differently than saturated fats after semi-starvation or fasting. But this is the first research, he believes, that shows differences in post-exercise fat metabolism after a meal.

The findings offer "one more reason to stay away from saturated fats," he noted, which are more readily stored by the body as excess pounds. So people hoping to stay at a healthy weight, he adds, should substitute monounsaturated fats for saturated fats and, of course, exercise.

SOURCE: Medicine & Science in Sports & Exercise 2002;34:1757-1765.

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