A food’s glycemic index (GI) refers to how it affects blood sugars shortly after it is eaten. The amount and type of carbohydrate in food, along with its fiber and fat, affect how quickly the food’s carbohydrates are absorbed, which affects blood sugar. Fiber and fat slow down carbohydrate absorption. Foods that raise blood sugars more tend to be digested more quickly, and are said to have a high GI. An overall diet with more foods lower in glycemic index can lead to lower levels of insulin, a hormone that helps control blood sugar and also promotes storage of extra calories in body fat.
However, a low glycemic index diet does not necessarily lead to long-term weight loss. In controlled clinical trials, when calorie level is kept the same, diets with an overall low glycemic index don’t lead to any greater weight loss, or body fat, than diets with an overall high glycemic index.
To lose weight, start by looking for nutrient rich food swaps to reduce your overall calories. Just because a food has a low glycemic index doesn’t mean it’s a healthful or low calorie food. There are foods low in calories and glycemic index like leafy green vegetables and dry beans that are nutrient-rich and help create an overall healthy diet that can promote weight loss. If you want to experiment and see whether paying attention to foods’ glycemic index makes a difference for you, add that strategy to the more important steps of choosing more low calorie foods and taking smaller portions of high calorie foods.
Karen Collins, MS, RDN, is AICR's Nutrition Advisor.