We know that overweight people tend to get Type 2 diabetes at a higher rate than lean people, but why? Evidence points toward a condition called insulin resistance. On the walls of muscle cells are specialized receptors that act as doors to let glucose pass from the bloodstream into the cell, where it can be burned for fuel. The receptors are normally locked, but insulin, a hormone produced by the pancreas, “unlocks” the doors and allows glucose to come in. If the receptors are resistant to insulin for any reason, glucose cannot enter the cell, and instead it stays in the bloodstream. As a result, blood glucose levels rise, and so does the risk of complications of diabetes.
The reasons for insulin resistance are not fully understood, but the evidence strongly suggests that excess fat is a leading cause, especially fat that accumulates in the abdomen. In simple terms, the fat clogs up the receptors. When this occurs, not only does it lead to elevated blood glucose levels and all the problems associated with that, but it often leads to hyperinsulinemia (excess insulin in the blood), a common condition in people who have Type 2 diabetes.
Hyperinsulinemia occurs when the pancreas, sensing that blood glucose levels are rising (because of insulin resistance), produces more and more insulin. While all this insulin may eventually lower blood glucose levels to normal, it may also damage the inner linings of the arteries and trigger other changes in body chemistry that encourage heart disease. (Whether hyperinsulinemia directly damages blood vessels or is simply a marker of underlying problems is a matter of controversy. There is no doubt, however, that hyperinsulinemia is associated with atherosclerosis.)
Together, insulin resistance and hyperinsulinemia are associated with a cluster of abnormalities collectively known as
syndrome X. Those abnormalities include high blood pressure, heart disease, high triglycerides, and decreased levels of HDL (”good”) cholesterol. Syndrome X has been shown to indicate a predisposition to diabetes and heart disease. Treatment includes drugs to lower blood pressure and triglycerides and to control blood sugar. But even the powerful drugs that are now available cannot reverse diabetes or obesity or completely eliminate the health risks that come with these conditions. That’s why it’s important to add lifestyle measures, including increased physical activity, to the treatment regimen.
Research shows that regular physical activity can improve insulin sensitivity (or lower insulin resistance) by 20% to 30% by building muscle and reducing body fat. It also helps lower blood sugar (exercise has an insulinlike effect) and control weight. Research is also very clear that it is almost impossible to maintain weight loss unless an individual is physically active.
Physical activity increases muscle and bone strength, increases the efficiency of the heart and lungs, reduces cholesterol levels, reduces blood pressure, increases energy, improves quality of sleep, improves appearance and posture, and reduces the risk of falling. It also increases mental acuity, enhances psychological well-being, improves mood, and reduces the symptoms of anxiety and depression (one study showed it may prevent depression).
The current “official” recommendations regarding physical activity are for all Americans over age two to accumulate 30 minutes of moderate-intensity physical activity on most, preferably all, days of the week. These recommendations were released in 1996 in the Surgeon General’s report, “Physical Activity and Health.” They suggest a “lifestyle” approach to physical activity and health, and they complement earlier guidelines that called for formal exercise 3-5 times a week, for 15-60 minutes, at 60% to 85% of maximum heart rate. These goals, set by the American College of Sports Medicine in 1978, are still worth pursuing for higher levels of fitness, but it is possible to improve your health and maintain good health with less vigorous activity. The new guidelines provide options for people who are unwilling or unable to participate in more formal exercise.