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Glycemic Index of Food Affects Body Fat, Muscle Loss, and Diabetes Risk

Aug. 26, 2004 -- You've heard how people can shed pounds on those controversial but popular low-carb diets. So how do rodents, those treasured laboratory test animals used to predict human results, eat their way to less body fat and better health?

By having plenty of carbohydrates, as long as they're low in their glycemic value.

This glycemic index (GI) indicates how much and how quickly blood sugar will increase after eating a carbohydrate-containing food. High-GI foods cause higher and more sudden spikes in blood sugar and have been linked to an increased risk of obesity and diabetes. Low-GI foods cause lower, slower rises in blood sugar. These foods have been associated with lower body fat and lower weight.

A low-glycemic diet plan differs from a low-carb one in that it encourages eating many types of carbohydrates initially forbidden in diets such as Atkins or South Beach. These include fruits, legumes, and grain products like bread, pasta, and cereals.

In new research published in this week's The Lancet, Harvard scientists add to evidence on just how effective a carb-centric, low-GI diet can be. So what's different about this study?

Rats Offer Evidence Humans Haven't

"There have been nearly 100 studies suggesting beneficial effects of a low glycemic diet, but no health organization in the U.S. officially recognizes their role," says researcher David S. Ludwig, MD, PhD, director of the obesity program at Children's Hospital in Boston. "That's because these studies are often criticized because it's difficult to separate effects of GI index in foods from those of other things that go along with it, like fiber. You can't keep humans keep locked up for a year, controlling everything about their diets."

But you can do this with caged rodents, so his team fed two groups of rats and mice -- both with identical weights at the study's start -- a diet comprised of nearly 70% carbohydrates that was identical in every way but one.

"They consumed exactly the same [amounts of] protein, fats, carbohydrates, and fiber -- and we went even further by feeding them in a way to keep their body weights identical," Ludwig says. "They only difference was the type of [carbohydrate] they received, one with either a low- or high-glycemic index."

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