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Dr. Kim A. Williams, the president-elect of the American College of Cardiology, often sees patients who are overweight and struggling with hypertension, Type 2 diabetes and high cholesterol. One of the things he advises them to do is to change their diets.

Specifically, he tells them to go vegan.

Dr. Williams became a vegan in 2003 because he was concerned that his LDL cholesterol — the kind associated with an increased risk of heart disease — was too high. Dr. Williams wrote about his reasons for going vegan and his belief in the cardiovascular benefits of a plant-based diet in a recent essay at MedPage Today.

Veganism has grown in popularity in recent years, reflected by the explosion of meat-free cookbooks and restaurants, and vegan-friendly products in grocery stores. But the endorsement by the man who is set to become the president of one of the country’s leading cardiology associations, which helps formulate health policies and guidelines, did not strike a totally positive chord.

“I didn’t know it would create such a firestorm of everything from accolades to protests,” said Dr. Williams, who is also the chairman of cardiology at Rush University Medical Center in Chicago. “The response was really loud, and much of it diametrically opposed.”

One person suggested he was promoting a radical diet to his patients based on the experience of a single person: himself. Others accused him of trying to get the college of cardiology to encourage everyone to go vegan, which he dismissed. And some critics suggested that Dr. Williams and the college were “unduly influenced by industry,” which baffled him.

“Who is the industry that promotes vegan dieting?” he asked. “Maybe the people who publish books on it. But that wouldn’t be considered industry, I don’t think.”

Dr. Williams said that his switch to veganism was prompted by a routine blood test about 10 years ago.

The test showed that his LDL cholesterol, which had been 110 a couple years earlier, had climbed to 170. Dr. Williams, who was about 49 at the time, said he assumed that age and physical activity had played a role; his once frequent levels of exercise had fallen, and cholesterol tends to rise as people get older. But he also suspected that his diet was not as healthy as he had thought.

“I was basically eating chicken and fish, no skin, no fried food and no red meat,” he said. “I thought it was healthy. But it was low fat instead of low cholesterol, which is what I needed.”

Researchers have long known that the relationship between the dietary cholesterol found in food and the cholesterol that circulates in the blood is complicated, varying greatly from one person to the next. In many people, the cholesterol in food has only a minor or negligible effect on blood cholesterol levels. But in some people, the effect can be more pronounced, which Dr. Williams said was probably the case with him.

He eliminated cholesterol from his diet by avoiding dairy and animal protein to see if there would be any effect. Instead of eating chicken and fish, he started eating vegetable-based meat substitutes like veggie burgers and sausages made from soy and other plant proteins and nuts. He also switched to almond milk from cow’s milk.

Six weeks later, his LDL had fallen to 90.

“It seems that the response to dietary cholesterol and other changes in diet are all genetically determined and quite variable,” he said. “One person might go from 170 to 150 by going to a plant-based diet. Another person might go from 170 to 90.”

Although LDL plays a role in heart disease, it is not the only factor. The plaque that accumulates in arteries consists not only of cholesterol, but immune cells that invade the artery walls as a result of chronic inflammation. Some researchers argue that this inflammation is the underlying problem in coronary artery disease. But Dr. Williams says he believes that being vegan can lower inflammation, too.

He said his enthusiasm for plant-based diets was based on his interpretation of medical literature. He cited observational studies of tens of thousands of members of the Seventh-day Adventist Church that found that people following vegetarian diets lived longer than meat eaters and had lower rates of death from heart disease, diabetes and kidney problems. And he pointed to research carried out by Dr. Dean Ornish, who found that patients who were put on a program that included a vegetarian diet had less coronary plaque and fewer cardiac events.

But Dr. Williams said he readily acknowledged that such studies were not conclusive.

Observational studies like those carried out on the Seventh-day Adventists show correlations, but they cannot establish cause and effect. And the study by Dr. Ornish was a small, randomized trial that, in addition to diet, included a number of interventions. Besides becoming vegetarians, the patients also gave up smoking, started exercising and had stress-management training. The extent to which diet played a role in the outcome is difficult to know.

Critics also point out that the Ornish diet restricts not only meat, but refined carbohydrates like added sugars and white flour, which have been implicated in cardiovascular disease in many studies.

Dr. Williams said he thought the research on the benefits of substituting nuts, beans and plant protein for meat was strong, but largely observational. But he was not arguing that the college of cardiology should promote veganism in its dietary guidelines. He said he would like to see large, extensive clinical trials of such diets “that pass muster” first.

Plenty of things that looked promising based on correlations that were identified in observational studies were later found to be problematic, he said, like vitamin E, hormone-replacement therapy, folic acid and, most recently, the HDL-raising drug niacin.

“There is a long list of things that, based on observational trials, we thought were beneficial, and then a randomized trial done for a long period of time showed that it wasn’t,” he said. “So I approach all of this with a sense of humility and an open mind.”

In the meantime, he said, he has made a habit of telling patients who are obese and plagued by metabolic problems like Type 2 diabetes to try exercising and eating less meat. And he discusses some of his favorite vegan foods with them.

“I recommend a plant-based diet because I know it’s going to lower their blood pressure, improve their insulin sensitivity and decrease their cholesterol,” he said. “And so I recommend it in all those conditions. Some patients are able to do it, and some are not.”