"We investigated mechanisms of action to explain the cholesterol-lowering effects of the pistachio diets," says Sarah K. Gebauer, recent Penn State Ph.D. recipient, currently a post-doctoral research associate, USDA Beltsville Human Nutrition Research Center.
The researchers conducted a randomized, crossover design, controlled feeding experiment to test the effects of pistachios added to a heart healthy moderate-fat diet on cardiovascular disease risk factors.
Controlled feeding experiments provide all the food eaten by study subjects for the duration of the study segment.
The participants began the study by eating a typical American diet consisting of 35 percent total fat and 11 percent saturated fat for two weeks.
They then tested three diets for four weeks each with about a two-week break between each diet. All three diets were variations on the Step I Diet, a cholesterol-lowering diet in general use.
The diets included, as a control, a Step I Diet with no pistachios and about 25 percent total fat and 8 percent saturated fat. The pistachio enhanced diets were Step I Diets with 10 and 20 percent of the energy supplied by pistachio nuts, respectively.
The 10 percent pistachio diet had 30 percent total fat and 8 percent saturated fat and the 20 percent pistachio diet had 34 percent total fat and 8 percent saturated fat.
The participants ate half their pistachios as a snack and the rest incorporated into meals.
The researchers report in the most recent issue of the American Journal of Clinical Nutrition that "Inclusion of pistachios in a healthy diet beneficially affects cardiovascular disease risk factors in a dose-dependent manner, which may reflect effects on Stearoyl CoA Desaturase (SCD). "
The researchers used the ratio of two fatty acids, 16:1 and 16:0 in plasma as a marker for SCD, an enzyme that is involved in the body''s synthesis of fatty acids.
"SCD is an important enzyme involved in cholesterol metabolism," says Gebauer.