Ease into a healthy, plant-based diet

Q: I'm thinking of becoming a vegetarian. But I need to be certain - is a vegetarian diet really better for your health?

A: The answer is: it depends. Just avoiding meats and eating only vegetables can be accomplished in both healthy and unhealthy ways. After all, a vegetarian who subsists on meat-free pizza and grilled cheese sandwiches isn't doing himself any favors.

And, believe it or not, I've had more than one "vegetarian" patient whose diet was like that.

However, for a while now, it's been clear that healthy, plant-based diets may improve long-term health. Such healthy vegetarian diets include proteins from vegetables (peas, spinach, broccoli, Brussels sprouts and many others) and carbs from whole grains.

Several recent studies have provided evidence of health benefits of plant-based diets. In one study, researchers found that vegetarians have the lowest average body mass index (BMI). Meat eaters have the highest BMIs. Excess weight is associated with a higher risk for Type 2 diabetes, heart disease and other illnesses.

Another study found that eating a vegetarian diet reduced the overall risk of all cancers compared with eating a non-vegetarian diet. And a third study showed that vegetarian diets were associated with a lower risk of death from all causes.

These studies were what are called observational studies. Large numbers of people were followed for a long time. Those people who chose to emphasize plant-based foods in their diets had better health. But the studies could not prove that the plant-based diets were the cause of the better health.

That kind of proof requires randomized trials, in which some people are chosen at random to eat plant-based diets and others are not. Because they are expensive to conduct, such randomized trials tend to involve smaller numbers of people followed for shorter times.

There have been quite a number of such randomized trials. They have generally shown that risk factors for heart disease, stroke and diabetes (like blood pressure, blood cholesterol and sugar) are better with plant-based diets.

A few studies have been large enough and long enough to actually show lower rates of these diseases and of premature death. So while I don't consider it proven beyond a doubt, I do think it is likely that healthy plant-based diets (particularly the Mediterranean diet) really are better for our health.

If you want to transition to a more plant-based diet, start slowly.

Deliberately make a vegetarian meal one day a week. (Meatless Mondays are popular these days.)

Then move to a few meatless meals per week.

You'll also have to change the way you think about your plate. Dinner won't center around a large chunk of meat.

Vegetarian meals mix proteins, fats and vegetables together. Stews, soups and one-pot meals with beans, whole grains and vegetables are popular options. Good sources of plant-based proteins and fats include avocados, peanut butter and nuts.

I've put a longer list of where to find plant protein and fats on my website, AskDoctorK.com.

• Dr. Anthony Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.