Measuring the health value of carbohydrates | News | Harvard T.H. Chan School of Public Health

Carbohydrate quality, glycemic index, metabolic health the focus at the Department of Nutrition’s annual Stare-Hegsted Lecture.

October 17, 2024 – In the late 1970s when low-carbohydrate diets were first becoming trendy, researcher David Jenkins and colleagues wanted to find a way to measure the health value of foods in this category. Otherwise, he recently told a Harvard T.H. Chan School of Public Health audience, it would be harder to justify encouraging people to eat more plant-based foods.

Jenkins, a physician and professor at the University of Toronto, and his team developed the glycemic index, a measure of how quickly and how much foods raise blood sugar levels after eating. He shared his research during the 19th annual Stare-Hegsted Lecture on Oct. 7 in Kresge G-2. The event, sponsored by the Department of Nutrition, honors department founders Fredrick Stare and D. Mark Hegsted.

Foods that have been made with highly processed grains and that contain little fiber—such as white bread—score high on the glycemic index, meaning that they are rapidly digested and cause substantial fluctuations in blood sugar. High consumption of these foods can increase the risk of developing type 2 diabetes and other chronic diseases. Foods with more intact grains such as steel cut oats receive lower scores for their more gradual effects on digestion and blood sugar.

The glycemic index and the glycemic load—a measure developed by other researchers that looks at how much digestible carbohydrate a food contains—should be used in addition to a food’s dietary fiber and whole grain content to assess its health value, Jenkins said. He and Walter Willett, professor of epidemiology and nutrition, recently published a paper on the topic, in which they also called for better nomenclature around classification of carbohydrate-rich foods in nutrition studies. They noted that, for example, “whole grains” can encompass both highly processed foods using whole grain flour—which are less healthy–and more healthful foods containing intact grains.

Jenkins cited additional research, including findings that people with higher body weight have a greater risk of negative health outcomes from high glycemic index diets, and studies suggesting that oxidative stress—a measure indicating an imbalance in the body’s ability to handle tissue-damaging oxygen-related molecules—caused by fluctuations in blood sugar might be the mechanism that causes health problems in people with high glycemic index diets.

Jenkins has also recently collaborated with Willett and other Harvard Chan School researchers on studies of the plant-based Portfolio Diet. A study published last year in Circulation found that it may benefit cardiovascular health.

– Amy Roeder

Photos: iStock / fcafotodigital; Binkai Liu