Updated June 25, 2002

Obesity, Type 2 Diabetes, and Physical Activity
What's the Connection?

by Richard M. Weil, M.Ed., C.D.E.

Diabetes

In 1980, 5.8 million Americans had diabetes. Today, the number of diagnosed cases is 10.3 million, a whopping increase of 77%. By 2020, if the increase in diabetes continues at the current rate, 18.2 million Americans will have it.

The risk of developing diabetes increases as BMI increases. A BMI over 22 kg/m2 is associated with an increased risk of diabetes, and the risk jumps approximately 25% for every unit above 22 kg/m2. The development of Type 2 diabetes is associated with weight gain after age 18, and it was recently estimated that 27% of new cases of diabetes were attributable to weight gain in adulthood of 11 or more pounds. Among persons who have been diagnosed with Type 2 diabetes, 67% have a BMI greater than or equal to 27 kg/m2, and 46% have a BMI greater than or equal to 30 kg/m2.

Almost 800,000 new cases of diabetes are diagnosed each year in the United States. The total yearly cost of treatment and prevention exceeds $98 billion dollars, with approximately $44 billion dollars spent on direct medical costs. A troubling feature of these numbers is that while Type 2 diabetes was once considered a disease of adults 50 years and older, approximately 25% of all new cases of Type 2 diabetes are diagnosed in teenagers.

It is widely believed that this new health crisis in youth is the result of inactivity, poor diet, obesity, and a genetic predisposition for diabetes. While there is no generally accepted definition of obesity as distinct from overweight in children and adolescents, the prevalence of overweight is increasing for children and adolescents in the United States, as is the level of physical inactivity.

Insulin resistance

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.)

Richard Weil is an exercise physiologist and a consultant to the Naomi Berrie Diabetes Center at Columbia Presbyterian Medical Center in New York City.

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