Exercise and Fat Burning

Patient Expert

Almost everyone tells us we should get as much exercise as possible. But the effects of exercise are sometimes controversial.

Exercise alone isn't apt to make you lose much weight. For example, walking, an excellent form of exercise because it doesn't put a lot of extra strain on your joints as running does, but burns very few calories.

The other day, I walked a total of about 3 miles, according to my pedometer. It said I'd burned 200 calories. Big deal. I could cancel that out with a couple of ounces of cheddar cheese or a little more than an ounce of almonds.

And, as pointed out by Gary Taubes in his book Good Calories, Bad Calories, exercise can just make you hungrier. So after exercising you might eat even more than enough to cancel out the calories burned by the exercise.

However, exercise has benefits that go beyond weight loss. For one thing, by getting your heart rate up (unless your idea of exercise is meandering), exercise strengthens your heart. It also builds muscle, and muscle burns more calories and takes up more glucose than fat.

Now there's proof of another benefit of exercise, especially for overweight people with diabetes. Exercise corrects a defect in fat burning that many overweight people have. Weight loss alone, on the other hand, does not correct this defect.

It has been shown that obese people have a decrease in the ability of skeletal muscle to oxidize fats.

Oxidize used this way means to metabolize, or burn, fats. If you want to lose weight, or avoid gaining weight, you want to be able to metabolize the fats you eat. If you don't, you'll store them in your fat cells. Even worse, when your fat cells get filled up, you'll start storing the fats in your liver and muscles. And this causes insulin resistance and can cause type 2 diabetes.

(There's another type of fat oxidation that produces damaged fats that can be harmful, but that's not what this study is about.)

Working at East Carolina University in North Carolina, Joseph Houmard and colleagues showed that this decreased fat oxidation occurred not only in the muscle cells in the subjects of the study, but also in muscle cells raised in culture from extremely obese donors.

It had previously been shown that a decrease in the ability to burn fats is associated with weight gain and tendency toward obesity. And there is evidence that this decreased ability to oxidize fats is associated with defects in the cells' mitochondria, the structures within cells that burn fats.

Exercise is known to increase the number of mitochondria, so the researchers wondered if it would also fix the defect in fat oxidation.

And it did. After a 10-week exercise program, the obese subjects were able to oxidize fats just as well as lean subjects.

The interesting thing is that weight loss, even large weight loss of about 50 kilograms (110 pounds) did not affect the ability to oxidize fats. Exercise was the key. A fit obese person would be able to oxidize fats better than a thinner formerly obese person.

Imagine the following scenario. You're born with a slightly defective ability to oxidize fats. This means you tend to put on weight, especially if your parents think that fat babies are healthy babies. So you are a bit chubby as a child.

Because you're chubby, the other kids don't choose you for sports teams, and you get less exercise. That makes you even less able to oxidize fats, so you get fatter and fatter. That makes it harder and harder to get exercise. And that makes your body less and less able to metabolize fats.

Finally, your fat cells get full, and the fat you can't oxidize ends up in your muscle cells, you get insulin resistance, and you eventually develop type 2 diabetes. A vicious circle.

But there's also a virtuous circle, perhaps illustrated by the David Mendosa's successful weight loss (the link was written before he'd reached his goal). He lost a little weight with the help of Byetta and eating a lot less. The weight loss allowed him to get more of the hiking exercise he used to enjoy. And the hiking, even though it probably didn't burn hundreds of calories, probably helped him to burn fats better.

Burning fats better made him lose even more weight, which made the exercise even easier, and he now exercises about 15 hours a week. A wonderful virtuous circle

His muscle lost fat, and his insulin resistance went down. The result was a thin man (a body mass index of 19.7, down from his top BMI of 40). He now takes no diabetes medications at all and has an A1c of 4.9.

So don't be discouraged by how few calories you burn with exercise. Exercise will help you burn fat. This effect of exercise may also explain why people who are able to keep their weight off long term are the ones who exercise.

Strenuous exercise like a couple of rounds of squash or a fast game of lacrosse will probably make you hungrier. But less-strenuous exercise like walking may not. If you have other medical conditions like bad hips or arthritis that don't allow you to do much walking, just do what you're able to do. Water exercises can be gentler than running or walking.

Exercise may be the key you need to get your diabetes under control.