Atkins Diet Tougher on Heart After Weight Loss

April 2 -- WEDNESDAY, April 1 (HealthDay News) -- In the "maintenance" phase that occurs after initial weight loss, the popular Ornish and South Beach diets seem to be easier on the heart than the high-fat, low-carbohydrate Atkins regimen, a new study finds.

Unlike numerous studies that have evaluated diets to see which might be better at achieving weight loss, this study, funded by the U.S. National Institutes of Health, looked at what happens to cholesterol levels and other cardiac risk factors when dieters reach their goal weight and remain on the diet.

The study involved 18 healthy people, with an average body-mass index (BMI) of 22.6 (18.5 to 24.9 is considered normal weight). Participants completed four weeks each on the Atkins (50 percent fat), South Beach (30 percent fat) and Ornish (10 percent fat) diets, in random order and with a four-week "washout" period between each diet. The study was done from January to December 2006.

The switch between diets meant that "each person served as his own control," explained principal investigator Dr. Michael Miller, director of the Center for Preventive Cardiology at the University of Maryland Medical Center in Baltimore.

At the start and after each four-week diet, the researchers evaluated cholesterol levels and other cardiac risk factors. They also looked at three-day food records at the end of each diet phase. And they checked blood vessel functioning by measuring blood vessel dilation in the arm.

They found that "as you increase the amount of saturated fat [in the diet], blood vessel dilation is reduced," Miller said. Healthy vessel dilation is important to proper blood flow.

"The diet that performed the worst [on the blood vessel test] was the Atkins diet," Miller said. "It contains more saturated fat."

Participants ate about 30 grams of saturated fat a day while on the Atkins diet, compared to about 14 grams on South Beach and about 3 grams while on Ornish.

"We like to say saturated fat should be below 7 percent of total calories," Miller said. "So, if your caloric intake is 2,000, saturated fat should be about 14 grams [or less] daily."