A new research study from Loma Linda University (LLU) demonstrates that naturally occurring antioxidants in pecans may help contribute to heart health and disease prevention; the results were published in the January 2011 issue of The Journal of Nutrition.
Pecans contain different forms of the antioxidant vitamin E — known as tocopherols, plus numerous phenolic substances, many of them with antioxidant abilities. The nuts are especially rich in one form of vitamin E called gamma-tocopherols. The findings illustrate that after eating pecans, gamma-tocopherol levels in the body doubled and unhealthy oxidation of LDL (bad) cholesterol in the blood decreased by as much as 33 percent. Oxidized LDLs may further contribute to inflammation in the arteries and place people at greater risk of cardiovascular problems. “Our tests show that eating pecans increases the amount of healthy antioxidants in the body,” says LLU researcher Ella Haddad, DrPH, associate professor in the School of Public Health department of nutrition. “This protective effect is important in helping to prevent development of various diseases such as cancer and heart disease.”
These findings are from a research project designed to further evaluate the health benefits of pecans, according to Dr. Haddad. She analyzed biomarkers in blood and urine samples from study participants (a total of 16 men and women between the ages 23 and 44) who ate a sequence of three diets composed of whole pecans, pecans blended with water, or a control meal of equivalent nutrient composition. The pecan meals contained about three ounces of the nut. Samples were taken prior to meals and at intervals up to 24 hours after eating. Following the test meals composed of whole pecans and blended pecans, researchers found that amounts of gamma-tocopherols (vitamin E) in the body doubled eight hours after both meals, and oxygen radical absorbance capabilities (ORAC — a scientific method for measuring antioxidant power in the blood) increased 12 and 10 percent respectively two hours after the meals. In addition, following the whole-pecan meal, oxidized LDL cholesterol decreased by 30 percent (after 2 hours), 33 percent (after 3 hours), and 26 percent (after 8 hours).
“This study is another piece of evidence that pecans are a healthy food,” says Dr. Haddad. “Previous research has shown that pecans contain antioxidant factors. Our study shows these antioxidants are indeed absorbed in the body and provide a protective effect against diseases.” Research from Loma Linda University published earlier in the Journal of Nutrition showed that a pecan-enriched diet lowered levels of LDL cholesterol by 16.5 percent — more than twice the American Heart Association’s Step I diet, which was used as the control diet in that study. Similarly, the pecan-enriched diet lowered total cholesterol levels by 11.3 percent (also twice as much as the Step I diet).
Beta-carotene is the precursor to vitamin A and gamma-tocopherol is a common form of vitamin E. Lutein is found in dark green leafy vegetables and is important in vision and healthy skin. All three compounds are oil soluble vitamins.
Antioxidants are of interest because oxidized low-density lipoproteins (LDL) are implicated in inflammation and plaque buildup inside blood vessels. Antioxidants should prevent LDLs from oxidizing, migrating into the blood vessel walls and causing inflammation.
“Currently, studies on antioxidants do not show major benefits,” said Kris-Etherton. “Maybe we are not studying people long enough. Maybe there is something in the food that travels with the antioxidants. The antioxidant story is very disappointing to the scientific community.”
The reason for the disappointment is that studies on specific antioxidants currently do not show health benefits, but epidemiological studies seem to indicate benefits. Many people feel that we have not figured out antioxidants yet, said Kris-Etherton.
If antioxidants are important, then pistachios fit the bill as antioxidant-laden food.
The researchers conducted a randomized, crossover design, controlled feeding experiment to test the effects of pistachios on antioxidant levels when added to a heart healthy moderate-fat diet. Controlled feeding experiments provide all the food eaten by study subjects for the duration of the study period.
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.
Other researchers in the study include Sheila West, associate professor of biobehavioral health, Penn State; Sarah Gebauer, U.S. Department of Agriculture, Beltsville, Md. and Colin D. Kay, lecturer, University of East Anglia.
The Western Pistachio Association supported this work. Partial support also came from the NIH- supported General Clinical Research Center at Penn State.