Conducted by Wake Forest University School of Medicine, the research is reported in the current issue of the Journal of Nutrition.
"While everyone knows that eating more vegetables is supposed to be good for you, no one had shown before that it can actually inhibit the development of atherosclerosis," said Michael Adams, D.V.M., lead researcher. "This suggests how a diet high in vegetables may help prevent heart attacks and strokes."
The study used specially bred mice that rapidly develop atherosclerosis, the formation on blood vessel walls of fatty plaques that eventually protrude into the vessel's opening and can reduce blood flow. The mice have elevated low-density lipoprotein ( LDL), or "bad" cholesterol, which is also a risk factor for atherosclerosis in humans.
Half of the mice in the study were fed a vegetable-free diet and half got 30 percent of their calories from a mixture of freeze-dried broccoli, green beans, corn, peas and carrots. These five vegetables are among the top-10 vegetables in the United States based on frequency of consumption.
After 16 weeks, the researchers measured two forms of cholesterol to estimate the extent of atherosclerosis. In mice that were fed the vegetable diet, researchers found that plaques in the vessel were 38 percent smaller than those in the mice fed vegetable-free diets. There were also modest improvements in body weight and cholesterol levels in the blood.
The estimates of atherosclerosis extent involved measuring free and ester cholesterol, two forms that accumulate in plaques as they develop. The rate of this accumulation has been found to be highly predictive of the actual amount of plaque present in the vessels.
Adams said it is not clear exactly how the high-vegetable diet influenced the development of plaques in the artery walls.
"Although the pathways involved remain uncertain, the results indicate that a diet rich in green and yellow vegetables inhibits the development of hardening of the arteries and may reduce the risk of heart disease," said Adams.
He said that a 37 percent reduction in a certain marker of inflammation in mice suggests that vegetable consumption may inhibit inflammatory activity.
"It is well known that atherosclerosis progression is intimately linked with inflammation in the arteries," Adams said. "Our results, combined with other studies, support the idea that increased vegetable consumption inhibits atherosclerosis progression through antioxidant and anti-inflammatory pathways."
Numerous studies in humans have shown that a high-vegetable diet is associated with a reduced risk of cardiovascular disease, as well as with reductions in blood pressure and increases in "good" cholesterol. This is believed to be the first study to address the effect of increased vegetable consumption on the development or progression of atherosclerosis.
Despite compelling evidence supporting the health benefits of increased vegetable consumption, intake remains low, Adams said. The mean consumption is 3.2 servings per days, with about 40 percent coming from starchy vegetables such as potatoes.
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