Sick of Low-Carb Diets? Try Low-GI
Glycemic Index of Food Affects Body Fat, Muscle Loss, and Diabetes Risk
WebMD News Archive
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."
"The animals on the high-GI diet were gaining more weight with same amount of food, and we had to cut their food back increasingly over time to keep them at the same weight," he tells WebMD.
"But what was really interesting to us was that even though they maintained the same weight because they got less food, the high-GI group in both rats and mice doubled their body fat and had a reduction ... in muscle mass, which is exactly what you don't want.
"They also had increases in their blood sugars, insulin, lipids, and other disease risk factors, and their pancreas beta cells that make insulin looked like they were going through a scarring process. If continued, that suggests a high likelihood of getting diabetes."
When his team switched the diets midway through the study, and those high-GI-eating rodents were given the low-GI diets, these adverse changes reversed. Meanwhile, the rodents switched from the low- to the high-GI diets started to have the same problems with added body fat, less muscle mass, and signs of impending diabetes.