"But, until now, we did not know what component of the walnut was providing this benefit. Now we understand additional ways in which whole walnuts and their oil components can improve heart health," she said.
In a randomized-controlled trial, the researchers gave 15 participants with elevated blood cholesterol one of four treatments-either 85 grams 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, one hour, two hours, four hours and six hours after administering the treatments.
The researchers repeated this process for each of the remaining three treatments.
Results showed that a one-time consumption of the oil component in walnuts favorably affected vascular health.
In addition, consumption of whole walnuts helped HDL-good cholesterol-perform more effectively in transporting and removing excess cholesterol from the body.
"Our study showed that the oil found in walnuts can 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, graduate student in nutritional sciences, Penn State said.
"The walnut oil was particularly good at preserving the function of endothelial cells, which play an important role in cardiovascular health," she said.
According to the researchers, walnuts contain alpha-linolenic acid, gamma-tocopherol and phytosterols, which may explain the positive effects of the walnut oil treatment.
"Implications of this finding could mean improved dietary strategies to fight heart disease," Berryman said.
The study is set to be published in the Journal of Nutrition.