The lowdown on glycemic index and glycemic load


If you have diabetes, you probably know you need to monitor your carbohydrate intake. But different carbohydrate-containing foods affect blood sugar differently, and these effects can be quantified by measures known as the glycemic index and glycemic load. You might even have been advised to use these numbers to help plan your diet. But what do these numbers really mean — and just how useful are they?

What these numbers measure

The glycemic index (GI) assigns a numeric score to a food based on how drastically it makes your blood sugar rise. Foods are ranked on a scale of 0 to 100, with pure glucose (sugar) given a value of 100. The lower a food's glycemic index, the slower blood sugar rises after eating that food. In general, the more cooked or processed a food is, the higher its GI, and the more fiber or fat in a food, the lower its GI.

But the glycemic index tells just part of the story. What it doesn't tell you is how high your blood sugar could go when you actually eat the food. To understand a food's complete effect on blood sugar, you need to know both how quickly it makes glucose enter the bloodstream and how much glucose it can deliver. A separate measure called the glycemic load does both — which gives you a more accurate picture of a food's real-life impact on your blood sugar. Watermelon, for example, has a high glycemic index (80). But a serving of watermelon has so little carbohydrate that its glycemic load is only 5.

Should you eat a low-GI diet?

Some nutrition experts believe that people with diabetes should pay attention to both the glycemic index and glycemic load to avoid sudden spikes in blood sugar. The American Diabetes Association, on the other hand, says that the total amount of carbohydrate in a food, rather than its glycemic index or load, is a stronger predictor of what will happen to blood sugar. And some dietitians also feel that focusing on the glycemic index and load adds an unneeded layer of complexity to choosing what to eat.

The bottom line? Following the principles of low-glycemic-index eating is likely to be beneficial for people with diabetes. But reaching and staying at a healthy weight is more important for your blood sugar and your overall health.

If you'd like to give low-glycemic-index eating a try, click here to see our table of the glycemic index and load for over 100 common foods.

And for more information on how to live well — and eat well — with type 2 diabetes, buy Healthy Eating for Type 2 Diabetes, a Special Health Report from Harvard Medical School.

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