Study Compares Three Popular Diets for Risk of Cardiovascular Problems
For immediate release: November 06, 2007
Study measured risk factors in the absence of weight loss
Three popular diets, the Atkins, South Beach and Ornish, may all help you take off weight, but which one puts you at higher risk of heart disease after only one month?
Michael Miller, M.D., director of preventive cardiology at the University of Maryland Medical Center in Baltimore and associate professor of medicine at the University of Maryland School of Medicine, and a team of researchers compared the three diets for their impact on cholesterol, their effect on the lining of blood vessels and the presence of inflammation associated with hardening of the arteries. Dr. Miller presented the findings of the study, “Comparative Effects of Three Popular Diets on Lipids, Endothelial Function and Biomarkers of Atherothrombosis in the Absence of Weight Loss,” on November 6, 2007, at the American Heart Association's Scientific Sessions in Orlando, Florida.
Dr. Miller found that people on the Atkins Diet, which is 50 percent fat, experience increased levels of “bad” (LDL) cholesterol, as well as a negative change in blood vessel dilation and an increase in markers for inflammation. The South Beach Diet is 30 percent fat, while the fat content of the Ornish Diet is 10 percent.
Eighteen healthy adults (nine men and nine women) completed the study. They were randomly assigned one of the diets for one month, and then they ate their normal diet for one month. Following that, they began the second diet, and, after another month with their normal diet, switched to the third diet.
Volunteers were weighed each week while they were on the test diets. The diet was adjusted if there was more than a two-pound weight difference.
The researchers used blood tests to determine levels of blood fats, including cholesterol, and markers for inflammation. They used ultrasound equipment to measure whether blood vessels dilated after a month on each diet, which is a healthy response, or whether the vessels constricted, an unhealthy response.
Dr. Miller says he was surprised by the extent of some of the changes in such a short time, particularly the pro-inflammatory characteristics from the Atkins Diet. “Some markers of inflammation were increased by as much as 30-40 percent during the Atkins phase,” says Dr. Miller, “whereas during the South Beach and Ornish phases, the markers either were stable or went down, some by as much as 15-20 percent.”
This study took the unusual tack of not including weight loss to investigate the connection between dieting and heart disease, which is the leading cause of death in the United States.
Recent studies have focused on the impact of diets on weight loss. But there has been little research on the impact of certain diets on heart disease risk factors such as the effect on the lining of blood vessels and the presence of inflammatory markers. Because the benefits of weight loss may initially mask the impact of these other risk factors, the University of Maryland researchers did not want study participants to lose weight.
Dr. Miller adds that many people on the Atkins Diet cannot stick to it, so the weight starts coming back. Because of that diet's tendency for inflammation, he says weight gain on Atkins could be a double whammy.
Bottom line: “We don't recommend the Atkins Diet. Why not start out with a diet that will be healthier for you in the long run after weight loss?” says Dr. Miller.
The study was supported by a Veterans Affairs Merit award to Dr. Miller and a grant from the National Institutes of Health.
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