WASHINGTON — Here's another way in which exercise may help a person avoid an early death: It fights insulin resistance syndrome, which may affect millions of American.
"My guess is 10% to 25% of the population is insulin resistant," said Dr. Robert Sherwin, a professor at Yale School of Medicine and president-elect of the American Diabetes Assn. There are no statistics on exactly how many people have the condition, he said.
People with insulin resistance syndrome have double or triple the risk of heart disease, said Dr. Barbara V. Howard, president of MedStar Research Institute, a part of the Washington Hospital Center. And virtually everyone who develops adult-onset diabetes starts with insulin resistance, she said.
Insulin resistance syndrome, also known as syndrome X, is a combination of conditions.
One is overweight--especially weight over the belt, such as a potbelly, as opposed to weight around the hips. The other indications show up on blood tests. These include above-normal cholesterol levels and higher readings on glucose tests commonly used to check for diabetes. People with insulin resistance also may have elevated blood pressure, Howard said.
The locus of all these signs and symptoms is a growing inability to use insulin. Muscle cells become less able to let the hormone guide nutrients through cell membranes and into the cells.
The pancreas tries to overcome the resistance by producing more insulin. But if the resistance grows, diabetes can result. And cholesterol changes linked to insulin resistance can lead to clogged arteries and heart disease, Sherwin said.
However, regular, calorie-burning aerobic exercise improves the factors that insulin resistance syndrome worsens. The cells get better at taking up insulin. Cholesterol levels and blood pressure retreat. Even the potbelly shrinks.
Exercise combined with diet forms one of the best ways to beat insulin resistance, Sherwin and Howard said. "If you can get a lot of weight loss, you can get them to almost normal insulin resistance, and the same with very heavy exercise," Howard said.
Sherwin stands by vigorous aerobic exercise, at least every other day, at sweat-producing levels found in an aerobic studio or a treadmill run. Anything less hasn't been proved to work, he said.
Howard, on the other hand, believes that even brisk walking can accomplish some good. "We have reasonably good epidemiological data that people who just do walking have lower rates of diabetes and heart disease," she said. From that, she inferred that they would have lower risk of insulin resistance syndrome.
Howard noted that syndrome X has found its way into several new books. One, by Dr. Burton Berkson of Las Cruces, N.M., is titled "Syndrome X." Berkson estimated that 65% of Americans have some symptom of syndrome X, but he said this was an indirect calculation based on diseases associated with syndrome X.
Berkson calls for fewer refined carbohydrates, such as sugary pastries, and more nonstarchy vegetables.
Sherwin and Howard both back eating fewer calories but don't think much of diets that recommend certain types of foods, such as more protein and less carbohydrate, or more carbohydrate and less protein. "Varying the distribution of calories has absolutely no effect at all," Howard said.
Berkson also disagrees with Sherwin and Howard in recommending more antioxidants, especially alpha lipoic acid.
Recent lab studies of rat tissue, mostly in Europe but some in the United States, have turned up indications that alpha lipoic acid may fight development of diabetes and heart disease. But Sherwin and Howard see nothing to establish that it can fight insulin resistance syndrome in people.
Berkson recommends exercise, but he has some disagreements even with the coauthors of his book, a nutrition writer and a nutrition counselor. They accept the idea that moderate exercise can help, but he believes exercise should be vigorous.
"I am on a regular exercise program at least three days a week," said Berkson, who is 60. "I run a mile or two, do curls, do presses, sit-ups and rowing exercises, and also punch the bag."