In a study conducted at Penn State University, researchers saw trial participants at risk for cardiovascular disease lower their central blood pressure by adding walnuts to their diet. Their results were measured against other study participants who only incorporated compounds found in walnuts (alpha-linolenic acid and oleic acid) into their diet without eating the nuts themselves.
"When participants ate whole walnuts, they saw greater benefits than when they consumed a diet with a similar fatty acid profile as walnuts without eating the nut itself," Penny Kris-Etherton, Distinguished Professor of Nutrition at Penn State, said. "So it seems like there's a little something extra in walnuts that are beneficial—maybe their bioactive compounds, maybe the fiber, maybe something else—that you don't get in the fatty acids alone."
Central blood pressure is the pressure exerted on the heart as blood flows toward the heart. It provides information about a person’s risk for developing cardiovascular disease in a similar fashion to the traditional way of measuring blood pressure in the arm, which measures the pressure moving away from the heart.
Dr. Kris-Etherton says the study suggests the ability of walnuts to lower central pressure may also decrease the risk of cardiovascular disease.
Researchers recruited 45 study participants between the ages of 30 and 65 who were overweight or obese. They were all given similar “run-in” diets the two weeks leading up to the randomized trial.
"Putting everyone on the same diet for two weeks prior to the start of the study helped put everyone on the same starting plane," Researcher Alyssa Tindall said. "The run-in diet included 12 percent of their calories from saturated fat, which mimics an average American diet. This way, when the participants started on the study diets, we knew for sure that the walnuts or other oils replaced saturated fats."
The participants were randomly assigned to one of three study groups after the two-week lead up period. All three groups ate diets that had less saturated fat than their run-in diet. One group incorporated whole walnuts into their diet while the others substituted the whole nuts for the main compounds the nuts contain.
The participants stayed on the diets for six weeks at a time and rotated between diets until they experienced all three. After each diet period the participants were tested for blood pressure as well as other cardiovascular risk factors and the best results were found in ones who consumed the whole walnuts.
"Walnuts contain alpha-linolenic acid—ALA—a plant-based omega-3 that may positively affect blood pressure," Tindall said. "We wanted to see if ALA was the major contributor to these heart-healthy benefits, or if it was other bioactive component of walnuts, like polyphenols. We designed the study to test if these components had additive benefits."