Cholesterol-lowering, low fat diets have abounded in recent years in the quest to reduce the risk of heart disease, the most familiar being the American Heart Association’s "Step II" diet, which confines dietary fat to less than 25% of calories and replaces the lost fat with carbohydrates. But recent research into the effects of monounsaturated fats (MUFAs, found in olive and certain other oils) suggests that low fat may not necessarily be the best way to ensure a healthy heart. Kris-Etherton and her colleagues at Pennsylvania State University made an across-the-board comparison of three diets: the Step II diet (25% fat), a diet high in MUFAs (34-36% fat), and the average American diet (34% fat). The high MUFA diets decreased cardiovascular risk by an average of 20.6%, versus a 12% reduction in risk for the Step II diet.

The high-MUFA diet goes against the conventional wisdom of heart disease prevention in that it is even higher in fat than the average American diet. Instead of replacing lost dietary fats with carbohydrates, the high MUFA diet makes up the "fat equation" with increased amounts of several different monounsaturated fats. In order to expand the choices available to heart-healthy consumers, the researchers set out to test the efficacy of other sources of MUFA’s than olive oils--with focus on peanut butter and peanut oil.

Of the 22 subjects who completed the study, those with the highest initial LDL concentrations achieved the greatest reductions in cardiovascular risk on the high MUFA diet, ranging from16% to 25% . The added advantage of the high MUFA diet over the Step II diet was that it brought down LDL cholesterol while not affecting HDL cholesterol. The Step II diet tends to bring down both LDL and HDL cholesterol concentrations, thus negating some of its own beneficial effects.

Subjects on high MUFA regimens who consumed the "peanut butter diet" attained nearly the same health benefits as those who consumed the "olive oil diet", or a 21% reduction in cardiovascular risk vs. 26% for olive oil. An accompanying editorial by Elaine Feldman stresses the biochemical similarities between olive and peanut oils, and the extra benefits conveyed by peanuts’ high protein content (25-30 %). Peanuts are not true nuts, but are actually legumes, and are unique in the plant kingdom in that they may contain the heart-healthiest of the saturated fatty acids.

Kris-Etherton, P M et al.
High-monounsaturated fatty acid diets lower both plasma cholesterol and triacyglycerol concentrations.
Am J Clin Nutr 1999; 70:1009-15.