Evaluating a food by its glycemic index has been promoted as yet another way to lose weight.

People love to find new ways to categorize and evaluate foods. Whether it’s by calories, fat grams or food groups, we are always on the lookout for helpful advice on making good dietary choices. We are particularly interested in advice that will help us lose weight. And recently, evaluating a food by its glycemic index has been promoted as yet another way to lose weight.
Not so long ago, it seemed like everyone was saying, “Limit fat and you’ll lose weight,” and food manufacturers created many new fat-free products. For some people, fat-free became synonymous with “eat all you want.” Many of these folks ended up eating too many calories and too many carbohydrates (fat-free products tend to be high in carbohydrates), which resulted not in weight loss, but in weight gain. Too many carbohydrates in the diet can also cause changes in blood fat levels that increase heart disease risk.

How do carbohydrates affect your body?

When your body consumes more calories than it needs, it saves those extra calories as fat. Your body is an expert at converting carbohydrate molecules into fat molecules. Your body can also convert extra protein into fat. So when you consume extra calories of any sort, you gain weight.

A high-carbohydrate diet can cause an increase in a type of blood fat known as triglycerides. Most of these triglycerides are manufactured by the liver and are sent to the fat cells for storage. Researchers believe that people with high triglyceride levels are at greater risk for developing heart disease.

Some people have responded to this research by limiting dietary carbohydrates. Other people have asked further questions, such as, are all carbohydrates bad? And if so, how can we tell the good carbohydrates from the bad ones?

Can a food’s glycemic index tell you if it is a good carbohydrate?

A food’s glycemic index tells you how quickly after the food is eaten that its carbohydrates appear in the blood as sugar. As researchers continue to explore the link between diet and health, some evidence suggests that a rapid rise in blood sugar caused by a high carbohydrate load triggers a high insulin response. Insulin is the hormone that tells the body’s cells to let in the sugar from the blood. It also tells the body to store extra calories as fat.

Some new diets on the market suggest that limiting your diet to foods that do not cause a rapid rise in blood sugar is a more healthful way to eat, and that such diets can lead to weight loss and prevent heart disease. Thus, they encourage people to consult tables listing the glycemic index of a food, and to choose foods with low values (low means the carbohydrates from those foods enter the bloodstream more slowly).

Knowing the glycemic index of a particular food is not very helpful, however. Nutritionists rarely recommend glycemic index tables to their clients for several reasons. First, a food’s glycemic index can be misleading. If foods have a high glycemic index, but only a relatively small amount of carbohydrates in a typical portion size, the overall glycemic load is not harmful. Second, the glycemic index will change if that food is consumed with other food. Protein, fiber and fat slow the absorption of carbohydrates. People who must be careful about blood sugar regulation, such as diabetics, are counseled by nutritionists to use an exchange diet that balances carbohydrates with protein and fat.

Prevent carbohydrate overload, weight gain and heart disease.

Instead of worrying about a food’s glycemic index, keep an eye on portion sizes and consume carbohydrates with foods that are high in fiber and protein, and with moderate amounts of heart-healthy fats. Limit empty calorie foods that are high in saturated fats, sugar and refined flour, to occasional treats that you savor and enjoy. Eat plenty of fruits, vegetables, beans and whole grains. Limit daily calorie consumption to prevent weight gain and to gradually lose weight if you are overweight. Enjoy plenty of physical activity, rest and relaxation so that you limit food cravings due to stress and fatigue.

Barbara A. Brehm, Ed.D., is professor of exercise and sport studies at Smith College, Northampton, Mass.

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