Harvard Health Letter

Conversation with a Harvard expert

Dr. David S. Ludwig is a nutrition and obesity researcher at Harvard-affiliated Children's Hospital Boston. His research has focused on the harmful health effects of high–glycemic load foods. He is author of Ending the Food Fight, a book about children's nutrition and weight.

What are glycemic index and glycemic load?

Glycemic index is a measure of how controlled amounts of food affect blood sugar and insulin. Glycemic load takes portion sizes into account, and tends to be a more practical guide. High–glycemic load foods raise blood sugar because they get digested far too quickly. The body responds with a massive outpouring of insulin, to keep blood sugar from going too high. But for many people there is an overshoot, and blood sugar crashes a few hours after the meal.

Why are high–glycemic load foods bad for us?

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