By: David A Fein, MD
Spend 30 minutes on a treadmill and it is likely that readout on the console will tell you that you have burned hundreds of calories. In fact, most exercise equipment dramatically overstates how many calories you actually burn during exercise. But is that really what matters when it comes to trying to get rid of those love handles? A pound of fat contains about 3,500 calories. Since an hour of moderate exercise is actually likely to only burn an additional 200-300 calories, it would take about 15 hours on the treadmill just to lose one pound of fat. But researchers at the University of Florida have found another, potentially even more important, effect of exercise that may help you lose weight.
The findings, published in the American Journal of Physiology, Endocrinology and Metabolism, found that exercise helps to convert white fat to brown fat. The effect is due to a surge in a hormone known as Irisin that occurs when the heart or other muscles are exerted. Irisin appears to work by boosting the activity of certain genes and a protein that are critical to converting white fat cells into brown fat cells.
White fat cells are basically just fat storage. It is where your excess calories go when you eat more than your body can utilize at the time.
Brown fat is more closely related to muscle cells than white fat cells and are metabolically much more active. It is brown because of a higher level of mitochondria in the cells. Mitochondria are involved in generating energy. The fat stored in brown fat cells is burned to help produce body heat. So these fat cells actually burn calories instead of just storing them.
The presence of brown fat in babies is critical for their ability to maintain their body temperature. As we reach adulthood, the amount of brown fat decreases but some remains, primarily in the upper chest, neck and around the kidneys.
In addition to helping maintain body temperature, activation of brown fat has been shown to lower cholesterol and triglycerides in the blood and to help protect against atherosclerosis. Brown fat activity may also be important in maintaining bone density.
Irisin production following exercise not only increased brown fat, it also suppressed formation of white fat cells. In human fat tissue cultures Irisin reduce the number of white fat cells by 20- to 60 percent. This may suggest that Irisin can reduce fat storage in the body.
So that calorie counter on your treadmill may not be all that important after all. Instead of focusing on the number of calories you burn with exercise, it may be that exercise has more direct effects on reducing fat stores, improving cardiac health and promoting strong bones. That’s all the more reason why short bursts of exercises throughout your day may be more important than more prolonged but less frequent exercise.