The study involved assigning the participants four different diets which were to be stuck to for two weeks each with a two week break in between each one.
Throughout the study levels of antioxidants (beta-carotene, gamma-tocopherol and lutin) were measured along with levels of bad cholesterol.
Participants began by eating a typical American diet in which 11 percent of their daily calorie intake was saturated fats and 24 percent from unsaturated fats. After a two week break they began their second diet which was intended to lower cholesterol, then their third which was the low cholesterol diet but with 10 percent of calories coming from pistachios and then the final diet in which the 10 percent pistachio intake was increased to 20 percent.
During diet 3 the pistachio intake was at around 1.5 ounces per day and this was doubled to 3 ounces when the intake was increased to 20 percent.
Researchers found that whilst participants were on the pistachio diets the blood levels of all three antioxidants increased significantly compared to the initial diet.