Study casts light on speed of weight loss

Why some people fail to shed pounds easily is a mystery that perplexes scientists and frustrates dieters, who often are blamed for lack of willpower.

But a new report shows that it may simply be biology at work and suggests an easy and effective way to overcome this flaw.

Researchers at Children's Hospital in Boston compared how 73 young, overweight adults fared on two weight-loss programs. Half the participants consumed a traditional, low-fat diet that included refined carbohydrates such as white rice, bread and sugary breakfast cereal.

The other half ate a diet rich in complex carbohydrates such as fruit, vegetables and whole grains.

Both groups received the same nutrition and exercise counseling.

Both diets produced the same small weight loss -- an average of about 2 pounds over 18 months, far less than what most dieters dream of.

But when the researchers analyzed the results further, they discovered a group of superlosers who shed five times more weight than other participants and maintained that loss throughout the study.

What separated the superlosers from the rest? How quickly their bodies produced the hormone insulin after eating.

Slow insulin producers lost the same small amount of weight on both diets. Fast insulin producers did even more poorly on the low-fat diet with processed carbohydrates. But they became superlosers when they dined on complex carbohydrates such as fruit, vegetables and whole grains, and slightly higher amounts of healthy fat.

The findings could help explain "why some people do very well on a weight-loss diet and others do very poorly on the very same regimen," notes David Ludwig, director of the Optimal Weight for Life Program at Children's Hospital and lead author of the report, which was published in the May 16 edition of the Journal of the American Medical Association.

The results may help physicians guide some overweight and obese people to try eating according to the glycemic index, a system that ranks food according to how much it raises blood sugar and spurs insulin production.

Highly processed carbohydrates -- sugar and white bread, for example -- are considered the benchmark against which other foods are measured. Foods that raise blood sugar higher than either of these foods are considered high glycemic index foods. Those that raise blood sugar less than these two foods are ranked as lower glycemic index foods.

Trouble is, few people eat one-food meals. So scientists have developed the glycemic load, a system that takes into account the glycemic index of a food and how much of the food is eaten.

"But it's a hard concept to understand," says David Heber, director of the University of California, Los Angeles Center for Human Nutrition.

Besides, few people want to eat according to numbers.

The good news is that you don't have to: High glycemic foods are generally highly processed foods, with minimal amounts of fiber and lots of sugar.

Low glycemic foods include the healthy and smart choices from fruit -- whole, not juice and dried fruit which are usually higher in sugar -- vegetables, beans, nuts and whole grains.

When in doubt, take the water test. Just drop a little bit of a food in a glass of water. If it dissolves quickly, it has a high glycemic index.

But just because a food has a low glycemic index doesn't mean that it's healthy. "Steak and creme brulee both have a low glycemic index," Heber notes. "But they are loaded with fat and calories. You can gain weight on anything if you eat enough of it. It doesn't matter what it is."

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