Oct. 6, 2010 -- Regularly eating a handful of walnuts can affect the blood pressure response to stress, according to a new study.

“People who show an exaggerated biological response to stress are at higher risk of heart disease,” study author Sheila G. West, PhD, of Pennsylvania State University, says in a news release. “We wanted to find out if omega 3-fatty acids from plant sources would blunt cardiovascular responses to stress.”

Her team of researchers studied 22 healthy adults with elevated levels of LDL or bad cholesterol. The participants were provided all their meals and snacks during three separate dietary interventions lasting six weeks each.

Diets included an "average" American diet without nuts, a second diet that included 1.3 ounces of walnuts (about 18 walnut halves) and a tablespoon of walnut oil substituted for some of the fat and protein in the average American diet, and a third diet that included walnuts, walnut oil, and 1.5 tablespoons of flaxseed oil. The three diets were matched for calories and were specifically designed so that no weight loss or gain occurred in any participant.

At the end of every diet trial, each adult had his or her stress levels raised in two ways:  by being asked to give a speech and by having one foot immersed in ice cold water. During both tests, researchers measured blood pressure readings in the participants.

The result: Including walnuts and walnut oil in the diet lowered both resting blood pressure and blood pressure responses to stress by two to three points.
Walnuts Reduce Stress

“This is the first study to show that walnuts and walnut oil reduce blood pressure during stress,” West says. “This is important because we can’t avoid all the stressors in our daily lives.”  The study, she says “shows that a dietary change could help our bodies better respond to stress.”

Some of the participants also underwent a vascular ultrasound examination to measure artery dilation.  The results showed that adding flaxseed oil to the walnut diet significantly improved this test of vascular health.  The researchers have previously shown that adding flax to walnuts also lowered C-reactive protein levels, indicating an anti-inflammatory effect that West says could reduce the risk of cardiovascular disease.
Study Supports Previous Research

Walnuts are known to be a rich source of fiber, antioxidants, and unsaturated fatty acids, particularly alpha-linolenic acid.  Alpha-linolenic acid is an omega-3 fatty acid, which the researchers say could explain the beneficial effects on blood pressure.

"Note that we provided everything that the participants ate during the six-week diet periods," West says in the email. "We removed some of the 'bad fat' in the control diet and replaced it with 'good fats' from walnuts, walnut oil, and flax oil."  So, though participants were eating nuts and oils in place of other foods, the walnut diets were not higher in calories.

West says that people who "stick with one serving of nuts" daily in place of another snack or meal containing fat should not gain weight, which, in itself, can cause health problems.

Primary funding for the study came from the California Walnut Commission of Sacramento, Calif. West and fellow researcher Penny Kris-Etherton, PhD, also of Penn State, say they received research grants from the California Walnut Commission and have served on its advisory committee.