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posted: 7/2/2012 5:59 AM

Low-fat diet after weight loss may spur pounds to return

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By Nicole Ostrow

Eating a low-fat diet after losing weight may cause the pounds to return, according to research that recommends a low-glycemic diet, one that doesn't cause spikes in blood sugar, for weight maintenance and total health.

A diet rich in vegetables, fruits and minimally processed grains that raise blood sugars slowly allowed the body to burn about 150 calories more a day than eating a diet low in fats, said David Ludwig, senior author of the study in the Journal of the American Medical Association. While a diet low in carbohydrates burned 325 calories more a day than the low-fat menu, it raised the risk of heart disease, the study found.

When people lose weight, their metabolism slows and allows the pounds to return, Ludwig said. Only one in six adults who are overweight or obese will maintain at least 10 percent of their weight loss for one year, the authors wrote. The findings show that eating a low-glycemic diet -- food that doesn't cause blood sugar to surge and crash between meals -- is best for health and long-term weight maintenance, he said.

"All calories are not alike," said Ludwig, director of the New Balance Foundation Obesity Prevention Center at Children's Hospital Boston and a professor at Harvard Medical School. "Rather than trying to eliminate fat or carbohydrates choose the middle ground that lets you eat the widest variety of foods as long as the focus remains on the quality of the nutrients."

Two-thirds of U.S. adults are overweight and one-third are obese, according to the Atlanta-based Centers for Disease Control and Prevention. The obesity rate may rise to 42 percent of the U.S. population by 2030, the CDC said in a May 7 report.

The researchers in the study included 21 overweight and obese adults from ages 18 to 40 who achieved 10 percent to 15 percent weight loss. They were then put on three diets for four weeks each -- low fat, low glycemic and low carbohydrate.

They found that those on the low-glycemic diet burned calories the equivalent of an hour of light exercise compared with those eating foods low in fat, while those on a low-carbohydrate diet burned calories equal to an hour of moderate exercise without actually engaging in physical activity, Ludwig said.

The study's primary findings showed that about 40 more calories a day were burned while the body was at rest on the low-glycemic diet than on the low-fat diet. On the low-carbohydrate diet, about 70 calories more a day were burned while at rest than the low-fat diet.

The low-fat diet had the worst effect on insulin, so-called "good" cholesterol, or HDL, and triglycerides, Ludwig said. The low-carbohydrate diet had the worst effect on chronic inflammation and hormonal stress.

A low-glycemic diet, like the South Beach Diet and the Zone Diet, can help control hunger longer because the body absorbs sugar from the carbohydrates slower. Foods such as pears, apples, steel-cut oats and some pastas are considered low glycemic. Popcorn, watermelon and potatoes are deemed high glycemic, as they cause the body to store fat and can lead to overeating.

"Most people can lose weight for a few weeks or even a few months, but most people regain the weight after a year and then some," Ludwig said. "For weight loss and heart disease prevention, avoid diets that severely restrict any major nutrient either fat or carbohydrate. Instead focus on reducing the highly processed carbohydrates that cause surges and crashes in blood sugar like white bread, white rice, prepared breakfast cereals, those low-fat snack foods and concentrated sugars."

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