You May Not Need to Worry About Glycemic Index, Study Says

Scientists say it may not be useful when choosing foods.

white bread

Bread photo via

One could be forgiven for having more than a few questions when it comes to nutrition. Is fat healthy now? Am I supposed to cut carbs? Is there such a thing as too many avocados?

A new study from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University may knock one question off your list. It says glycemic index (GI)—you know, that phrase you always hear but don’t quite understand—may not be something you need to worry about.

Glycemic index is meant to measure how fast a food causes your blood sugar to rise after consumption. It was originally used mainly by people with diabetes, but has become a benchmark sometimes used to assess a food’s nutritional value: Low GI foods, such as nuts, keep your blood sugar steady, and are thus traditionally thought to be better choices than high GI foods, such as refined carbs, which cause a sharp spike. But the Tufts study suggests GI may not be as cut-and-dry as it seems.

Over the course of 12 weeks, roughly 60 healthy adults ate white bread multiple times under standardized conditions, then submitted to GI testing. In theory, the bread’s GI should have been the same each time. Instead, it varied by an average of 25 percent from person to person, and 20 percent within the same individual, likely due to differing metabolic responses to food. That means, depending on the instance, white bread could have been considered a low, medium, or high GI food.

The study does not mean that white bread is suddenly healthy, or that low GI foods aren’t—it just means your energy may be better spent choosing fresh, minimally processed, nutrient-rich foods than calculating glycemic loads.

“Based on our results, we feel strongly that glycemic index is impractical for use in food labeling or in dietary guidelines at the individual level,” lead author Nirupa Matthan said in a statement. “If your doctor told you your LDL cholesterol value could vary by 20 percent, it would be the difference between being normal or at high risk for heart disease. I don’t think many people would find that acceptable.”