The researchers used a randomized, crossover study design. Tests were conducted at the end of each six-week diet, and every participant consumed each of the three diets in random order, with a one-week break between. Diets included an "average" American diet - a diet without nuts that reflects what the typical person in the U.S. consumes each day. The second diet included 1.3 ounces of walnuts and a tablespoon of walnut oil substituted for some of the fat and protein in the average American diet. The third diet included walnuts, walnut oil and 1.5 tablespoons of flaxseed oil. The three diets were matched for calories and were specifically designed for each participant so that no weight loss or gain occurred. The walnuts, walnut oil, and flax oil were either mixed into the food in such offerings as muffins or salad dressing or eaten as a snack. About 18 walnut halves or 9 walnuts make up the average serving used by the researchers.

After each diet, the participants underwent two stress tests. In the first test, they received a topic; and they were given two minutes to prepare a three-minute speech, which they presented while being videotaped. The second stressor was a standard physical test of stress consisting of submerging one foot in ice-cold water. Throughout these tests, the researchers took blood pressure readings from the participants.

Results showed that average diastolic blood pressure -- the "bottom number" or the pressure in the arteries when the heart is resting -- was significantly reduced during the diets containing walnuts and walnut oil.

Walnuts are a rich source of fiber, antioxidants, and unsaturated fatty acids, particularly alpha linolenic acid, an omega-3 fatty acid, and these compounds could be responsible for the beneficial effects on blood pressure. Flax oil is a more concentrated source of omega-3 fatty acids than walnut oil, but this study did not test whether flax oil alone could blunt cardiovascular responses to stress.

"These results are in agreement with several recent studies showing that walnuts can reduce cholesterol and blood pressure," noted West. "This work suggests that blood pressure is also reduced when a person is exposed to stress in their daily life."

Source: Penn State