For the study, Dr. Ros and his colleagues recruited 24 nonsmoking adults with normal body weights and blood pressures. Half of the participants had normal cholesterol levels and half had moderately high levels. Each was asked to follow a cholesterol-lowering Mediterranean diet for two weeks prior to the study and throughout its duration. A Mediterranean diet includes foods low in saturated fat but high in fiber or monounsaturated fat, such as fruits and vegetables, whole grains and olive oil.
Study participants were randomly assigned to one of two groups. Each was provided with two high-fat meals, eaten one week apart. The meals were identical, consisting of a salami-and-cheese sandwich on white bread and a small serving of full-fat yogurt. For one meal, the researchers added about 5 teaspoons (25 ml) of olive oil. For the other, they added 40 grams of walnuts, or about eight shelled nuts.
According to their findings, both the olive oil and the walnuts helped to decrease the sudden onset of inflammation and oxidation in the arteries. These harmful processes, which typically follow consumption of high-fat meals, can lead to hardening of the arteries, or atherosclerosis, a precursor to heart disease.
But unlike olive oil, adding walnuts also helped to preserve the elasticity and flexibility of the arteries, regardless of people's cholesterol levels. This elasticity allows the arteries to expand when needed to increase blood flow to the body.
The walnuts contain arginine. Arginine is a precursor to nitric oxide. Nitric oxide is a signalling agent used by the body to (among other things) cause blood vessels to dilate and let more blood through. Saturated fats are known from previous research to cause the body to produce inflammation molecules which block nitric oxide production. But perhaps higher arginine availability counteracts that effect and keeps nitric oxide production higher.
"The inner lining of the arteries produces a substance called nitric oxide that is needed to keep the arteries flexible," Dr. Ros said. "When we eat high-fat meals, the fat molecules temporarily disrupt the production of nitric oxide, preventing the arteries from increasing blood flow in response to physical activity."
One of the nutrients found in walnuts, he said, is arginine, an amino acid used by the body to produce nitric oxide. Walnuts also contain antioxidants and alpha-linolenic acid (ALA), a plant-based omega-3 fatty acid. Olive oil does not contain ALA, a specific type of healthy, polyunsaturated fat.
The ability of walnuts to enhance nitric oxide production has other implications. Some drugs work by releasing nitric oxide (NO). Among the NO releasing compounds are Minoxidil for treating male pattern baldnessa and Viagra and Cialis for treating erectile dysfunction. There's a chance that consumption of walnuts might therefore provide other benefits as well.
|Share |||Randall Parker, 2006 October 15 06:28 PM Aging Diet Studies|