Going green may be heart healthy if the green you choose is pistachio nuts,
according to researchers at Penn State who conducted the first study to
investigate the way pistachios lower cholesterol.
"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.
They found the ratio of 16:1/16:0 was significantly lower, suggesting a
decrease in SCD activity, after eating the 20 percent energy pistachio diet
compared to the control diet which had no pistachios. Also, the change in the
16:1/16:0 ratio was correlated with the change in cholesterol, suggesting that
SCD activity may contribute to the lipid-lowering effects of pistachios. That,
accompanied by the dose-dependent effects of the pistachios, 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. The effects of the 10 and 20
percent energy diets showed a dose dependent effect on these ratios.
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 Penny Kris-Etherton, distinguished
professor of nutrition and primary investigator of the study."
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