A growing body of evidence suggests that a plant-based diet — one that focuses on vegetables, whole grains, and lean proteins — is the single best eating plan for your body and brain. It's been found to be ideal for losing weight, staying lean, and even keeping the mind sharp.

But a lot of people are doing it wrong.

For a recent study published in the Journal of the American College of Cardiology, researchers at the Harvard T.H. Chan School of Public Health analyzed the eating habits of more than 200,000 health care workers over the course of more than 20 years. They sought to find out whether there was any observable link between their eating habits and their risk of developing coronary heart disease.

Unsurprisingly, many of the health professionals stuck to a plant-based, vegetarian diet. But among the vegetarians, eating habits differed drastically — and in some cases appeared to be less healthy than the diets of the non-vegetarians.

The researchers were able to identify three main categories of vegetarian diets from their participants: a "healthy" plant-based diet centered around whole grains, fruits, and vegetables; an "unhealthy" plant-based diet that consisted mainly of refined carbohydrates like white bread and pasta; and an "overall" plant-based diet that was somewhere in between the two. At the end of the study period, those who had kept closest to the "healthy" plant-based diet were the least likely to suffer from coronary heart disease. Those who veered more toward the "unhealthy" plant-based plan were the most at risk.

"Not all plant foods are necessarily beneficial for health," the researchers wrote in their paper.

Still, plenty of research shows that when done correctly, plant-based diets win out over every other eating plan.

The key that this study highlights is that it is important not to fall back on refined foods like white bread and pasta. If you're thinking about switching to a plant-based diet, make sure you're eating plenty of whole grains like brown rice and whole grain bread in addition to vegetables and fruits.

The best plant-based diet for the body and mind

Cara Anselmo, a nutritionist and dietitian at New York's Memorial Sloan-Kettering Cancer Center, told Business Insider that she frequently advises her clients — vegetarian or not — to ramp up their intake of plant-based foods. She also tells them to cut back on red meat and refined carbohydrates like white bread.

To keep your energy levels up and help you feel healthy in the long term, your diet needs to feed more than your stomach, Anselmo told Business Insider. It has to satiate your muscles, which crave protein; your digestive system, which runs best with fiber; and your tissues and bones, which work optimally when they're getting vitamins from food.

A healthy plant-based diet's combination of whole grains, fruits, vegetables, proteins, and fats accomplishes that goal.

This balance is also key to keeping you full after a meal and energized throughout the day so you don't feel the need to overeat, Nichola Whitehead, a registered dietitian with a private practice in the UK, told Business Insider.

"You need to have a balanced meal — things like whole grains, fiber, and vegetables — in order to sustain your blood sugar. Empty calories [like white bread or white rice] give a temporary fix," she said.

Healthy plant-based diets also appear to significantly reduce the risk of certain diseases including heart disease, diabetes, and some types of cancer. Recent research also suggests that certain plant-based diets could help protect the brain from some types of age-related decline.

"When you look at overall dietary patterns it's a more whole-foods, plant-based diet that tends to be healthier in terms of less disease risk," Anselmo said. "People get caught up in things like, 'Well, how much iron or Vitamin C does this have?' But the reality is that the whole foods are just going to naturally be higher in those things."