Researchers at Penn State who conducted the first study to investigate the way pistachios lower cholesterol have determined that the delicious snack, like so many other nuts, has a positive effect on the heart.
"We investigated mechanisms of action to explain the cholesterol-lowering effects of the pistachio diets," says Dr. Sarah K. Gebauer, a research associate at the USDA Beltsville Human Nutrition Research Center who did much of this work in her PhD program at Pennsylvania State University.
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. Personally, I don't know how they ate only a controlled amount of pistachios . . . once I start, I can not stop. That appears to be the major problem with the nut, plus the sodium content in salted pistachios.
They found the pistachio eaters had significantly lower cholesterol, suggesting that pistachios have a terrific lipid-lowering effect. This study begins to unravel the way in which pistachios improve cardiovascular health.
Compared to the control diet, the 20 percent pistachio diet lowered LDL cholesterol -- bad cholesterol -- about 12 percent and the 10 percent energy pistachio diet lowered LDL cholesterol by 9 percent that suggests a 9 to 12 percent decrease in coronary heart disease risk. The relationships of total cholesterol to HDL cholesterol and LDL cholesterol to HDL cholesterol may be more powerful predictors of cardiovascular risk.
However, the researchers note that the reduction in LDL cholesterol observed was seven times greater than would be expected from only the fatty acid profile of pistachios. They suggest that the lipid lowering effects not only reflect the fatty acid profile of the diet, but also are the result of other bioactive substances in pistachios, perhaps phytosterols and fiber.
"Our study has shown that pistachios, eaten with a heart healthy diet, may decrease a person's CVD risk profile," says Dr. Penny Kris-Etherton, professor of nutrition and who is listed as the primary investigator of the study.