The Atkins diet slashes carbohydrates while allowing foods high in saturated fat, like butter and red meat, while South Beach emphasizes moderate amounts of unsaturated fat, like olive oil, and "good" carbohydrates like vegetables and beans. The Ornish plan is a vegetarian diet that is very low in fat overall and intended to prevent and treat heart disease.
Researchers had 26 healthy, non-obese adults follow each of the diets for one month apiece. The goal was not to have them lose weight, but to study the biological effects of each eating plan -- namely, the effects on cholesterol, blood vessel function and inflammation.
Each participant's diet was calculated to provide enough calories for weight maintenance.
After one month, the study found, the Atkins diet had caused participants' "bad" LDL cholesterol to tick upward, on average. In contrast, the South Beach and Ornish plans led to a nearly 12 percent and 17 percent reduction, respectively.
In addition, the Ornish diet seemed to have the best impact on blood vessel function. Blood vessel function also correlated with the amount of saturated fat participants had been eating -- improving as saturated fat intake declined.
The study is published in the Journal of the American Dietetic Association.
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