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Some Starchy Foods May Contribute to Overeating

By Judy McBride
March 1, 1999

WASHINGTON, March 1--Meals high in carbohydrates that are rapidly digested and absorbed appear to trigger a series of hormonal and metabolic changes that promote overeating in obese people, according to a new study at a U.S. Department of Agriculture research center. The study findings are published in the March issue of Pediatrics.

“These findings provide the first solid evidence that carbohydrates are one piece of the puzzle in determining what makes some people overeat,” Agriculture Secretary Dan Glickman said.

Scientists use the term “high glycemic index” (GI) to describe carbohydrates that are rapidly digested and absorbed. The Boston researchers conclude that high GI meals set off a chain of actions that cause people to overeat.

On three separate days, a week or more apart, researchers fed a group of obese teenage boys breakfast and lunch with a high, medium or low glycemic index. Then they measured changes in the boys’ blood glucose, fatty acids and insulin and other hormones for five hours after breakfast. Blood glucose and insulin rose highest and fastest after the high GI breakfast. Within a few hours, however, blood glucose and fatty acids dropped significantly, triggering a stress response, indicated by a rise in the hormone adrenalin.

After the boys consumed an identical lunch, they were encouraged to select what they wanted from a platter of foods when they felt “very hungry.” The subjects ate nearly twice as much after a high GI meal than after a low-GI meal.

About one-fifth of U.S. children and one-third of adults are now significantly overweight, despite a significant drop in fat intake in recent years. Researchers David S. Ludwig at Children's Hospital of Boston and physiologist Susan B. Roberts at the USDA Human Nutrition Research Center on Aging at Tufts University believe that the results likely apply to the middle-aged and elderly as well.

According to Roberts, high GI foods include refined grain products and potatoes, as well as sources of concentrated sugars, such as sodas and fruit juices. Some starchy foods have higher GIs than table sugar. Moreover, many of the low-fat foods that have flooded grocery shelves are also high in calories. Vegetables and fruits generally have a low GI.

Roberts said the findings do not support weight-loss diets based entirely on the glycemic index because many low-GI foods, including steak, butter and ice cream, are high in calories. These low-GI foods trigger overeating because they are palatable and calorically dense.

Ludwig, who directs the obesity program at Children’s Hospital, said GI has a role in weight regulation along with genetics, physical activity, psychological factors and other dietary variables.

Scientific contact: Susan B. Roberts, PhD, Energy Metabolism Laboratory, USDA Human Nutrition Research Center on Aging at Tufts, Boston, Mass., phone (617) 556-3238, roberts_em@hnrc.tufts.edu; or David S. Ludwig, M.D., PhD, The Children’s Hospital, Boston, Mass., phone (617) 355-4878, ludwigd@hub.tch.harvard.edu.