Moderate Exercise Does Not Make Your Body Burn Fat For Hours

How often have you heard someone at the gym or on a late-night infomercial say that working out will help you burn fat for hours after you stop? Too many times to keep count? Well, Edward Melanson, an associate professor of medicine at the University of Colorado, Denver would beg to differ and he presents his views in Exercise and Sports Sciences Reviews.

WebMD reports on these findings. The problem is that moderate exercise, especially that doen for less than an hour, has little effect on the so called “24-hour oxidation of fat”:

“It’s not that exercise doesn’t burn fat,” Melanson says. “It’s just that we replace the calories. Exercise increases the capacity to burn more fat. But if you replace those calories, that is lost.” [WebMD]

To test the level of fat burning after exercise, Melnason’s team used 28 participants in a study. Of these, 10 were lean and endurance-trained, 10 were lean but untrained, while the remaining 8 were obese and untrained. Their exercise involved riding a stationary bike for about an hour burning 400 calories. After the exercise, while calories burned were indeed higher for all the test subjects, the 24-hour test revealed that instead of fat, it was carbohydrates that were being burned.

The reason for this, according to Melanson, is that what we eat after an exercise affects the kind of macro-nutrient our body uses first for fuel:

For instance, eating as little as 240 calories of carbohydrate during the hour before exercise can reduce fat burning during exercise, and the boost in fat burning during exercise can be “blunted” for up to six hours after eating a meal, says Melanson, citing other research. [WebMD]

These disappointing results are just for moderate exercisers who workout for an hour or less. High intensity exercisers or those practising interval training are bound to notice much better results. Still, the bottom line is simply this: if you are trying to lose weight, it’s dangerous to assume you can eat whatever you want or inwhatever quantity you want, simply because you have “done your exercises for the day”.

You cannot change the laws of science: take in more calories than you expend, and you will gain weight. No question about it.