Oct. 9, 2006 -- A handful of walnuts protects your arteries from the shock of a high-fat meal, Spanish researchers find.
The finding suggests that nuts are a more important part of the heart-healthy Mediterranean diet than olive oil. The Mediterranean diet is low in saturated fats but high in monosaturated fats, particularly olive oil.
Heart health depends on healthy, flexible arteries. When you eat a high-fat meal, it temporarily stuns your arteries. They stiffen and become less able to expand in response to exercise. Over time, this repeated damage contributes to hardening of the arteries.
But if you eat walnuts along with a fatty meal, the fat has much less of a short-term effect, find Emilio Ros, MD, PhD, and colleagues. Ros is director of the Lipid Clinic at Hospital Clínico, Barcelona, Spain, the central location for the study.
"People would get the wrong message if they think that they can continue eating unhealthy fats provided they add walnuts to their meals," Ros says in a news release. "Instead, they should consider making walnuts part of a healthy diet that limits saturated fats."
Ros serves on the scientific advisory board of the California Walnut Commission, which partially funded the study and provided it with nuts.
Walnuts: The Anti-Salami?
Ros and colleagues studied 24 nonsmoking, normal-weight adults. They all had normal blood pressure. Half of the participants had elevated cholesterol but were not taking any medications for it. Two weeks before and during the study, these volunteers went on a strict Mediterranean diet -- low in fats and meats but high in fiber, fruits, and vegetables.
The volunteers then ate a salami-and-cheese sandwich on white bread with a small serving of full-fat yogurt. Half the volunteers had walnuts (about eight nuts) added to this meal, while the other half had about 5 teaspoons of olive oil added to the meal.
After one week, the same high-fat meal was served and the volunteers who had previously had walnuts were switched to olive oil; those who had olive oil were switched to walnuts.
Sophisticated tests showed that the high-fat meal had less of a blood-vessel effect on those who ate the walnuts than on those who ate the olive oil.
Ros notes that walnuts contain a fatty acid called alpha-linolenic acid. This plant-based fatty acid is similar to omega-3 fatty acid found in fish.
University of Maryland researcher Robert A. Vogel, MD, who did not participate in the study, said the results show that the right foods -- in the right combination -- can protect one's health.
"This demonstrates that the protective fat from walnuts actually undoes some of the detrimental effects of a high-saturated-fat diet, whereas a neutral fat, such as olive oil, does not have as much protective ability," Vogel says in a news release. "This raises a very interesting issue because many people who eat a Mediterranean diet believe the olive oil is providing the benefits. But this research and other data indicate that's not true. There are probably other factors in the diet, including that it is a relatively rich source of nuts. This is not to say that olive oil is bad, but it’s not the key protective factor in the Mediterranean diet."
Ros and colleagues report their findings in the Oct. 17 issue of the Journal of the American College of Cardiology.