THE VALUE OF EXERCISE

by Arturo Rolla, MD

(FROM THE EDITOR: We recently encountered the following exchange, on one of the Internet's many diabetes discussion lists. We thought it worth sharing. Arturo Rolla, MD, the author, is an endocrinologist at Harvard Medical School.)

Q: I have heard many times that exercise helps to lower insulin resistance. My question: Is it a fleeting or a cumulative effect? In other words: If I exercise today, will it help me for some time after the exercise; or does only an active person who exercises everyday benefit from exercise?

A: Exercise has many different effects. Just on carbohydrate metabolism there is an acute decrease in insulin resistance with increased uptake of glucose in the muscles, therefore the BGs decrease.

If the exercise is prolonged and you use up all the glycogen in your muscle (muscle glycogen depletion) the muscles continue to take up glucose for hours after you stopped exercising. That's why it is not unusual to get hypoglycemia from exercise at night!

If you exercise on a regular basis you decrease the fat mass and specially the abdominal fat (the worst). The decrease in (abdominal) fat tends to improve insulin resistance, most likely by decreasing the levels of circulating Free Fatty Acids. So, prolonged exercising has a prolonged or more permanent effect on insulin resistance.

There is also a possibility that well trained muscle fibers (more and larger) by themselves may be more sensitive to insulin, but that has not been shown clearly--as far as I know.