WASHINGTON, DC — A new study challenges the long-held, yet long-unproven, assumption that high-glycemic index (GI) foods increase risk of obesity, while low-GI foods promote fat loss.

Published in Advances in Nutrition, the comprehensive study, “Perspective: Does Glycemic Index Matter for Weight Loss and Obesity Prevention? Examination of the Evidence on ‘Fast’ Compared with ‘Slow’ Carbs,” analyzed data on 43 cohorts from 34 publications (comprising nearly two million adults) to assess if dietary glycemic index impacts body weight.


“In recent years, there’s become a popular distinction between ‘fast’ and ‘slow’ carbs, specifically characterizing ‘fast’ carbs as unhealthy and fattening. We found tens of thousands of entries about that on Google,” said study co-author Glenn Gaesser, PhD, professor of exercise science at Arizona State University. “We knew many published studies contradicted the underlying reasoning behind the fast carbs hypothesis, but none of them were mentioned. We felt a thorough review of literature was necessary to set the record straight.”

It took weeks to complete the study, but it reached a definitive conclusion: “GI, as a measure of carbohydrate quality, appears to be relatively unimportant as a determinant of BMI or diet-induced weight loss.” In simpler terms, that “fast carbs do not make you fat,” said Gaesser. “Contrary to popular belief, those who consume a diet of high-GI foods are no more likely to be obese or gain weight than those who consume a diet of low-GI foods. Furthermore, they are no less likely to lose weight.”

Glycemic index, as a measure of carbohydrate quality, appears to be relatively unimportant as a determinant of BMI or diet-induced weight loss.


These findings are especially relevant alongside the skyrocketing better-for-you (BFY) trend in the bakery and snack markets. While consumers have an idea in their heads of what BFY means, studies like this one can challenge those beliefs.

According to study co-author Julie Miller Jones, PhD, LN, CNS, the trouble with the BFY movement is that there’s simultaneously no definition and a million definitions.

“These definitions come from public health professionals, advertisers, bloggers, doctors, fitness experts,” said Jones. “Some have expertise and some just have the attitude that ‘I eat, therefore, I know … and write about it.’”

Jones suggests that some researchers and journalists mistake associations for causations. When asserting that high-GI diets cause increased weight, they may be looking at other factors that cause weight gain in a high-GI diet, such as insufficient fiber or vegetables.

“Bakers need to meet consumer needs, even if they’re not based on the best evidence, so some bakers will choose to reformulate or sell some low-GI products,” said Jones. “It’s always a good idea to add more fiber and whole grain, when possible, as less than 10% of the population meets the daily requirements.”


Both Gaesser and Jones say they have three wishes for consumers, GI and diets:

  1. If consumers would focus on what this food contributes to my diet in terms of nutrients and calories, not GI.
  2. If consumers would meet the recommendations of the Dietary Guidelines to “make half their grains whole.”
  3. If consumers would consider the recommended number of servings of core grain foods (breads, tortillas, rolls, cereals, etc.) to meet suggested dietary requirements and calorie needs. At the same time, they should consider non-core foods (cookies, cakes, pastries, doughnuts, etc.) as indulgences and eat them once in a while as a treat.

While this study examined the correlation between weight and GI, Gaesser expressed interest in building on the research by examining the relationship between GI and the risk of chronic diseases such as diabetes and cancer.

Siddhartha Angadi, PhD, was another co-author of the study. This study was supported by the Grain Foods Foundation, a group of thought leaders and advocates for all grain foods to support happy and healthy lives. For more information about the research findings, and to learn more about grain foods’ role in a healthful diet, visit