Counting Carbs? Understand Glycemic Index and Glycemic Load

You’ve probably heard of glycemic index and glycemic load. Some studies suggest that sticking to foods with a low glycemic index may help prevent diabetes, cardiovascular disease and cancer. Some claim it helps with weight loss. The truth is, we don’t know all the answers yet. Here’s what you need to know.

The glycemic index and load concern carbohydrates, or carbs—one of the main types of nutrients in our diets. Carbs with a simple chemical structure are called sugars. Sugars are found naturally in foods like fruits, vegetables and milk products. They’re also added to many foods and drinks. Complex carbs, like starches and fiber, are found in whole-grain breads and cereals, starchy vegetables and legumes.

Your digestive system changes the carbs you eat into glucose, a type of sugar that your body uses for energy. Simple carbs are more quickly digested and absorbed than complex ones, so simple carbs can raise your blood glucose levels faster and higher.

People with diabetes need to manage their blood glucose levels. High blood glucose can damage tissues and organs. In time, it can lead to heart disease, blindness, kidney failure and other problems. If you have diabetes, controlling your blood glucose will prevent or delay these health complications. So it’s important to understand how foods and drinks affect your blood sugar.

“The evidence seems to support the concept that the more complex carbohydrates will lead to better blood sugar control than the more simple sugars,” says Dr. Myrlene Staten, an NIH diabetes expert.

Researchers developed the glycemic index to measure the quality of carbs in foods. It shows how the carbs in different foods raise blood sugar. White rice, for example, has a higher glycemic index than brown rice, which has more complex carbs.

But it’s not just the types of carbs that matter. The more carbs you eat, the more your blood sugar rises. “The glycemic index really doesn’t take into consideration how much you eat,” explains Dr. Somdat Mahabir, who studies cancer risk at NIH.

That’s why researchers came up with the concept of glycemic load. It captures both the types of carbs in a food and the amount of carbs in a serving. Essentially, it shows how a portion of food affects your blood sugar. Many things affect the glycemic load, including food processing, how ripe a fruit is, how a food is prepared and how long it’s been stored.

Studies of people who use these concepts to guide their diets have found mixed results. “There’s evidence to show that glycemic index and glycemic load are not associated with body weight,” says Dr. Catherine Loria, an NIH expert on nutrition and heart health. “There’s really not enough evidence to show if glycemic index is related to heart disease.” A possible link to cancer is also being explored.

Glycemic index and glycemic load aren’t things you’ll see on a label, so they’re not easy to use. But labels do show helpful information: calories, total carbohydrates, sugars and fiber.

“It makes sense for everybody, not only diabetics, to eat the more complex carbohydrates because they will be more gradually absorbed, and blood sugar highs and lows will be smaller,” Staten says. Whole foods with complex carbs will give you more minerals and vitamins, too, and are usually good sources of fiber.