The study, published in the current (February) issue of the American Journal of Clinical Nutrition, showed that a moderate-fat diet might be a better choice. Christine L. Pelkman, Ph.D., assistant professor of nutrition in the UB School of Public Health and Health Professions, is first author on the study.
The dietary intervention trial involved two groups of overweight participants assigned to eat meals containing the same number of calories, but different percentages fat. The groups were monitored so that both lost the same amount of weight. After six weeks, those on the moderate-fat diet had a healthier heart profile than those on the low-fat diet.
Participants who consumed a diet containing 33 percent fat (moderate fat) reduced their cardiovascular risk by 14 percent, based on their lipid profiles, findings showed. Those consuming a diet containing 18 percent fat (low fat) reduced their lipid-based risk by nine percent.
Moreover, after a four-week weight maintenance phase, moderate-fat dieters maintained their levels of beneficial cholesterol (HDL), improved the ratio of HDL to total and non-HDL cholesterol and lowered the concentration of triglycerides, also harmful to heart health.
Low-fat dieters experienced an initial drop in triglycerides, but at the end of the study, these fats had rebounded, HDL levels were lower and the ratio of HDL to total and non-HDL cholesterol didn't change.
"We don't know very much about the effects of a higher-fat versus a lower-fat, weight-loss diet on the blood lipid profile in overweight adults," said Pelkman. "The emphasis has been on low-fat diets for both weight loss and for reducing the risk of heart disease.
"We know that losing weight improves the lipid profile, but that doesn't tell us if weight loss alone or the composition of the diet is responsible. We wanted to take weight loss out of the equation and see if there is an effect of diet composition during weight loss." Pelkman conducted the research while a postdoctoral researcher at Penn State.
The study group consisted of 53 overweight or obese men and women between the ages of 20 and 67 who were assigned randomly to either the low- or moderate-fat diet. All meals were provided, and weight loss was kept constant at an average of 2.4 to 2.7 pounds a week. Both diets met current saturated fat and cholesterol recommendations.
Carbohydrates replaced the calories from saturated fats in the low-fat diet, while monounsaturated fats replaced saturated fats in the moderate-fat diet. Chemical analysis of the diets validated the composition of the two diets.
During the weight-loss period, both groups lowered their total and LDL cholesterol, but the low-fat group also experienced a 12 percent drop in HDL cholesterol. Triglycerides dropped in both groups, as well. However, during the weight-maintenance phase, there was a reversal of the weight-loss induced drop in triglycerides and a reduction in HDL cholesterol compared to baseline in the low-fat group, but not in the moderate-fat group.
"These results show that although weight loss does improve the lipid profile, a moderate-fat, weight-loss diet reduces risk more than a low-fat, weight-loss diet, so dieters don't need to cut out all the fat to improve their risk profile," Pelkman said. "Monounsaturated fats can be a healthy part of a weight-loss diet."
Additional researchers on the study were Valerie K. Fishell, Deborah Maddox, and Penny M. Kris-Etherton, Ph.D., all of Penn State; Thomas A. Pearson, M.D., MPH, Ph.D., from the University of Rochester; and David T. Mauger, Ph.D., from the Penn State College of Medicine.
The research was supported in part by the Peanut Institute.