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ove over, low-fat diets. More and more experts are recommending plant-based diets to reduce the risk of heart disease and other chronic conditions such as diabetes and cancer. But are all plant-based diets equally beneficial? And must they be all-or-none eating strategies, or is there a role for a semi-vegetarian or flexitarian approach?

The term plant-based diet often conjures up images of vegetarian or vegan fare. But it really means a diet that emphasizes foods from plants vegetables, fruits, grains, nuts, seeds, and the like not one that necessarily excludes non-plant foods.

The results of studies on the health effects of plant-based diets have varied widely, largely due to how these diets were defined. Some focused on vegetarian or vegan eating habits, others included some foods from animals. Notably, these studies tended to treat all plant foods equally, even though eating certain foods from plants, such as refined grains and sugar-sweetened beverages, is associated with a higher risk of developing diabetes or having a heart attack or stroke, while eating whole grains and produce are associated with lower risks.

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Thats why we were so interested to see the results of a recently published study performed by researchers at the Harvard T.H. Chan School of Public Health. Led by Ambika Satija, the team catalogued the diets of nearly 210,000 nurses and other health professionals based on their answers to food frequency questionnaires every two years for an average of 23 years. From these data, the researchers defined three versions of a plant-based diet: an overall plant-based diet that emphasizes the consumption of all plant foods and reduced the intake of animal foods; a healthful plant-based diet that emphasizes the intake of healthy whole grains, fruits, and vegetables; and an unhealthful plant-based diet that emphasizes the intake of less-healthy plant foods, such as refined grains.

In addition to detailing their food choices, the study participants also recorded other lifestyle choices, health behaviors, and their medical histories.

Over the course of the study, 8,631 participants developed coronary heart disease, which the researchers defined as a nonfatal heart attack or dying of heart disease. Those who followed an overall plant-based diet were slightly less likely (an 8 percent reduction) to have developed coronary heart disease than those who didnt.

But heres where things get interesting. Those who followed a healthful plant-based diet had a substantial 25 percent lower risk of coronary heart disease, while those who followed an unhealthful plant-based diet had a substantial 32 percent increased risk.

This study is certainly not the last word on the subject. As an observational study, it cant prove cause and effect like a randomized trial can. And the diet data came from self reports, which arent always accurate at measuring an individuals diet. However, these diet assessments were validated against multiple-week diet records and biomarkers. Overall, this work adds to the substantial evidence that a predominately plant-based diet reduces the risk of developing heart disease.

It has two important take-home messages. One is that a plant-based diet is good for long-term health. The other is that not all plant-based diets are equally healthy. The kind that deserves to be highlighted in dietary recommendations is rich in fruits and vegetables, whole grains, and unsaturated fats, and contains minimal animal protein, refined carbohydrates, and harmful saturated and trans fats.

In practice, this translates into eating mostly vegetables, fruits, whole grains, legumes, and soy products in their natural forms; sufficient good fats, such as those in fish or flax seeds, nuts, and other seeds; very few simple and refined carbohydrates; and little or no red meat, poultry, fish, eggs, and dairy. It also means choosing quality over quantity.

As we wrote in a commentary on the Harvard study, just as physical activity is a continuum some activity is better than none, and more is better so is diet. For anyone following a traditional American diet, heavy on the meat, its easier to make a change by starting with small dietary tweaks instead of embracing a precipitous shift to a vegetarian or vegan diet. Try the elimination game: cut out red meat from your diet then, after a couple weeks, eliminate other types of meat; and then do the same with dairy foods and eggs. Or try the Meatless Monday approach dont eat meat on Monday then gradually add more meatless days each week. No matter what approach you take to cutting out foods, try to add one or more new plant-based recipes to your cooking repertoire every week.

What you stand to gain is so much more than what you would give up.

Hena Patel, M.D., is a cardiology fellow and Kim Allan Williams Sr., M.D., is chief of the division of cardiology at Rush University Medical Center in Chicago.

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Not all vegan or plant-based diets are equally healthy - STAT