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 actual amounts of pistachios included in each diet were 1.5 ounces and 3 ounces for the 10 and 20 percent diets, respectively.

Both pistachio diets produced higher blood serum levels of beta-carotene, lutein and gamma-tocopherol than the typical American diet. Compared to the pistachio free Step I Diet, the pistachio-enhanced diets produced greater blood plasma levels of lutein and gamma-tocopherol. After eating both pistachio-enriched diets, the participants had lower oxidized-LDL concentrations in their blood than after the control Step I Diet.

When the researchers controlled for the change in LDL-cholesterol produced by the pistachio-enhanced diets, increases in beta-carotene and gamma-tocopherol were still associated with decreased oxidized-LDL for the 3-ounce pistachio-enhanced diet.

"Our results suggest that a heart-healthy diet including pistachios contributes to a decrease in serum oxidized-LDL levels, in part through cholesterol lowering, and also due to an added benefit of the antioxidants in the pistachios," said Kris-Etherton.

Source: Penn State