Penny Kris-Etherton, distinguished professor of nutrition at Pennsylvania State University in State College, and colleagues said in a randomized-controlled trial the researchers gave 15 participants with elevated blood cholesterol one of four treatments.
Some were given either 85 grams -- about 3 ounces -- of whole walnuts, 6 grams of skin, 34 grams of defatted nutmeat, or 51 grams of oil. The team evaluated biochemical and physiological responses in the participants before the treatments were administered and again 30 minutes, 1 hour, 2 hours, 4 hours and 6 hours after administering the treatments. The researchers repeated this process for each of the remaining three treatments.
The study, published online ahead of the June issue of the Journal of Nutrition, showed a one-time consumption of the oil component in walnuts favorably affected vascular health. In addition, consumption of whole walnuts helped high-density lipoprotein, the "good," cholesterol, perform more effectively in transporting and removing excess cholesterol from the body.
"Our study showed that the oil found in walnuts could maintain blood vessel function after a meal, which is very important given that blood vessel integrity is often compromised in individuals with cardiovascular disease," Claire Berryman, a graduate student in nutritional sciences, said. "The walnut oil was particularly good at preserving the function of endothelial cells, which play an important role in cardiovascular health."
Walnuts contain alpha-linolenic acid, gamma-tocopherol and phytosterols, which may explain the positive effects of the walnut oil treatment, the researchers said.
The California Walnut Board funded the research.
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