High body levels of the hormone insulin, seen in what is called "metabolic syndrome" (or "syndrome X") have gone from being an incidental finding among some overweight and inactive people to a major health concern that could mean a higher risk of diabetes, colon cancer, heart disease and stroke. Recent National Institutes of Health guidelines call for more attention to metabolic syndrome and insulin resistance.

Some fad diets claim to solve insulin abnormalities and weight problems, but those claims are not supported by the experts. In fact, they have been denounced in a recent review of popular diets as posing health risks all their own.

Insulin works by binding with receptors on cells, like a key that fits into a lock and opens the door for sugar to enter body cells. Insulin resistance occurs when normal amounts of insulin don't do this effectively. A cycle then begins, in which the body compensates by producing more and more insulin while becoming less and less able to use it.

With sugar unable to enter cells, insulin levels in the blood build up beyond normal ranges. Research suggests that high levels of insulin are often a sign that diabetes will develop within a few years. Two recent studies, however, showed that people with mild blood sugar elevations were able to make a 58 percent cut in their risk of developing diabetes through modest weight loss, regular exercise and balanced eating.

Metabolic syndrome is a constellation of symptoms that can include excess abdominal fat, high blood triglycerides, low HDL ("good") cholesterol, high blood pressure and insulin resistance (with or without blood sugar abnormalities). High insulin levels raise blood triglycerides, increasing heart attack and stroke risk.

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At the last annual research conference held by the American Institute for Cancer Research (AICR), Harvard Medical School's Dr. Edward Giovannucci reported finding a consistent link between high insulin levels and increased risk of colon cancer in the evidence he had reviewed. In laboratory studies, insulin enhances the growth of certain cells that are part of the very early stages of colon cancer.

AICR's landmark report on diet and cancer risk links sedentary lifestyle and obesity with greater risk of colon and several other cancers. Giovannucci's summary, published recently in the Journal of Nutrition, suggests that the strong relationship of insulin resistance to excess waistline fat and inactivity may be an important part of the cancer link. In fact, studies suggest that those who are most active may cut their risk of colon cancer in half.

While physical inactivity and excess body fat seem to be the primary reasons insulin resistance develops, some research suggests eating habits that cause frequent high blood sugar peaks may also be involved. Giovannucci's report notes that low-fiber starchy foods as well as sweets raise blood sugar quickly. Diets high in these foods seem especially dangerous for those who are sedentary, reportedly facing 4.5 times the colon cancer rate as those who are lean, active and eat a low-sugar, high-fiber diet.

While several low carbohydrate diets claim this research supports their use for weight control and good health, Circulation recently published a review that strongly disputes the claims for several such diets. The excess fat consumption that often results from these "fad" diets clearly raises risk of cancer, heart disease and other health problems.

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Eating carbohydrate foods (including bread, potatoes and pasta) in large portions may lead to high insulin levels, weight gain and unhealthy consequences. But completely avoiding carbohydrates - which supply fiber, vitamins and health-protective phytochemicals - is not the answer - portion control is.

Karen Collins, M.S., R.D.,C.D.N.