Can you explain why a study from The University of Sherbrooke in Canada showed that exercising three times a week improved insulin sensitivity in younger women but not in older women? (European Journal of Applied Physiology, October 2005) Insulin sensitivity measures the ability of your cells to respond to insulin. When cells fail to respond adequately to insulin, blood sugar levels rise too high, and you are more likely to suffer diabetes, obesity particularly in the abdomen, high blood pressure, heart attacks, strokes and nerve damage. Inability to respond to insulin is the most common cause of diabetes in North America. Exercise helps your cells respond to insulin because exercise empties muscles of their stored sugar. Empty muscles can absorb sugar from the bloodstream whenever you eat and prevent blood sugar levels from rising too high.

Thirty-five percent of adults in North America will become diabetic because they eat too much and exercise too little, because being fat fills your fat cells with fat, which blocks insulin receptors and prevents your body from responding to insulin. Insulin prevents your blood sugar from rising too high, particularly after you eat. So when your cells do not respond adequately to insulin, your pancreas produces very large amounts of insulin, which constricts coronary arteries to increase your chances of suffering a heart attack, stimulates your brain to make you hungry and causes fat to be deposited in your belly.

The only places that you can store extra sugar in your body are in your liver and muscles. When you eat, sugar passes from your intestines, into your bloodstream, and then into your muscles and liver. When your muscles are full of sugar, sugar can only enter your liver, and your blood levels rise too high. This causes sugar to stick to cells. Once stuck on a cell, sugar is converted to sorbitol which damages the cells to cause blindness, heart attacks, strokes, kidney damage and all the other side effects of diabetes. This study showed that younger women could exercise intensely enough to empty their muscles on a regimen of three times a week, but older women could not.

So most older people need to exercise every day to deplete their muscles of stored sugar. Younger people can exercise less frequently and to get the same results, as long as they exercise very vigorously during their three sessions per week.

Gabe Mirkin, M.D.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in Sports Medicine and three other specialties.

Dr. Mirkin's daily features on fitness have been heard on CBS Radio News stations since the 1970's. He has written 16 books including The Sportsmedicine Book, the best-selling book on the subject that has been translated into many languages. His latest book is The Healthy Heart Miracle, published by HarperCollins.

Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. A Boston native, Dr. Mirkin did his residency at the Massachusetts General Hospital. He has served as a Teaching Fellow at Johns Hopkins Medical School, Assistant Professor at the University of Maryland, and Associate Clinical Professor in Pediatrics at the Georgetown University School of Medicine. He has run more than forty marathons and is now a serious tandem bicycle rider with his wife, nutritionist Diana Mirkin.