Athletes are routinely advised to consume adequate dietary carbohydrate to fuel their active life-styles. So, it's not surprising that athletes (and the public in general) felt betrayed by their forks when the New York Times ran a front page headline earlier this year stating that "Pasta Makes You Fat." This news was especially confusing and disturbing in light of current advice from public health agencies to include more pasta and other complex carbohydrates in the diet.

This article, and the wide media coverage it received, caused many people to question the accuracy of present nutrition recommendations. It's helpful to examine the issue of insulin resistance to make sense of this latest "carbo-bashing" fad.

Some diet experts now suspect that carbohydrates pose particular problems for individuals who have insulin resistance -- which is estimated to affect 10 to 25 percent of all Americans. These foods have also been implicated in contributing to "Syndrome X," a cluster of risk factors that increase the risk of developing heart disease. Most of the confusion about carbohydrates centers around a basic misunderstanding of the function of insulin and how insulin resistant people respond to dietary carbohydrate.

In insulin resistance, the muscle, liver, and adipose cells are less sensitive to the actions of insulin -- most likely due to a reduced number of insulin receptors. The pancreas compensates by increasing insulin secretion to maintain normal blood glucose levels. People who are insulin resistant oversecrete insulin dramatically when they eat either simple or complex carbohydrates. In theory, this oversecretion of insulin causes more carbohydrate to be stored as fat instead of being burned for energy.

Unfortunately, the idea that carbohydrates can make insulin-resistant people fat is very misleading. Eating a high proportion of calories as carbohydrates does not make an insulin-resistant person overweight. It's the total caloric intake that's important. An insulin-resistant person must eat too many calories for insulin to lay down fat stores, not just a lot of calories from carbohydrate. Carbohydrates will be converted to fat only if they are eaten in excess.

By the same token, a person (insulin-resistant or not) cannot eat an unlimited amount of carbohydrates by cutting down on their fat intake. Reducing dietary fat does reduce total calories more than reducing dietary carbohydrate, because fat provides more than twice the calories by weight. However, cutting back on fat calories but adding them back in the form of carbohydrate calories won't produce weight loss. It's a simple fact of energy balance which holds true for people whether or not they are insulin resistant.

There is concern that a diet emphasizing carbohydrates will exacerbate Syndrome X in certain insulin resistant people. Syndrome X, a term coined by Gerald Reaven, M.D. of Stanford University, is used to describe a group of heart disease risk factors that include hypertension and lipid abnormalities (high triglycerides and low HDL levels). However, according to Xavier Pi-Sunyer, M.D., an obesity expert at St. Luke's Roosevelt Hospital Center in New York, very few insulin-resistant people react to high carbohydrate diets with signs suggestive of Syndrome X.

Reduction of excess weight and increased physical activity are more important in the treatment of insulin-resistance than the dietary percentage of carbohydrate or fat. Exercise and weight loss reduce triglycerides, increase HDL cholesterol, and lower blood pressure. In addition, both weight loss and exercise independently increase insulin sensitivity.

Weight loss allows the cells to more easily "recognize" insulin so that less insulin is required. Regular physical activity is important because muscle cells are the biggest users of insulin. Decreasing the muscle's insulin requirements through exercise cuts down on insulin resistance to a large extent. This means that insulin can bind more easily to the cell receptors and is more effective in promoting glucose uptake.

The last thing most athletes need to worry about is getting too much carbohydrate. As a group, athletes are unlikely to be insulin-resistant because they're lean and they exercise. Furthermore, athletes require dietary carbohydrate to maintain their muscle glycogen stores -- the predominant fuel for most sports. The only way they will gain weight is if they consume more calories than they expend. When this happens, blame the fork, not the carbohydrate.

Recommended Reading

Reaven, G.M. Role of insulin resistance in human disease, Diabetes, 1988; 37:1595-1607.

Haffner, S.M. et. al. Prospective analysis of the insulin-resistance syndrome (Syndrome X), Diabetes, 1992; 41:715-722.

Is pasta now on the "out" list too? Tufts University Diet & Nutrition Letter 1995; 13:4-6.