Plant-Based Diets: A Primer

What’s the big deal about plant-based diets?

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There was a time when vegetarianism was one thin euphemism away from just plain weird. Subsisting on plants seemed like some kind of kooky California fad or college experimentation and was discussed with an eye roll and hushed tone. Then again, there was a time when Whole Foods was the province of hippies, Bill Clinton ate burgers with bravado (the former commander in chief has since gone vegan to stave off heart disease), and vegetarianism marked the rare dietary restriction at a dinner party. Of course, we weren't quite so hungry then for solutions.

We all know Americans have become fatter but less nourished, and that we face a public health crisis, the likes of which we've never seen before. Our children, one-third of whom are overweight or obese, may, for the first time in our nation's history, be dealt a shorter life span than their parents. Blame it on a sedentary lifestyle coupled with the consumption of cheap, processed food. In any case, the prognosis has us scrambling to literally save our lives by learning how and what to eat. 

[See Why We're So Fat: What's Behind the Latest Obesity Rates.]

Meanwhile, food sensitivities, allergies, and intolerances, and about a million other complicated factors, from health concerns to culture and ideology, have created a nation of idiosyncratic diets, often as individual as the dieters themselves.

However, as data increasingly points to the protective and restorative power of so-called plant-based diets, many of us are turning to the whole fruits and vegetables our mothers and their mothers insisted upon. That's not to say Americans are adopting vegetarianism (vegetarians represent just 5 percent of the adult population, and a mere 2 percent identify as vegans, according to a July 2012 Gallup poll). Today, we talk about "plant-based diets." That means—most of the time, but we'll get back to this later—a diet with mostly, not exclusively, plants. Or, as popularized by the motto emblazoned on the cover of In Defense of Food, the best-selling book by investigative food journalist Michael Pollan: "Eat food. Not too much. Mostly plants."

"We now have much stronger evidence that replacing red meat with plant sources of protein such a nuts or legumes improves blood cholesterol fractions and is associated with lower risks of heart disease, stroke, and diabetes," says Walter Willett, chair of the department of nutrition at Harvard School of Public Health.

Such data, like studies supporting the health benefits of a Mediterranean-style diet, led to the emphasis on plant-based foods in the 2010 Dietary Guidelines for Americans, according to Linda Van Horn, professor of preventive medicine at Northwestern University Feinberg School of Medicine who chaired the dietary guidelines advisory committee. Those guidelines, which are released every five years by the U.S. Departments of Agriculture and Health and Human Services, showed that we're filling up on the wrong things—consuming, for example, nearly triple the recommended limit of solid fats and added sugars while getting only 15 percent of the whole grains and 59 percent of the vegetables we need.

"It's a double whammy," Van Horn says. "You're not only eating more of the things you shouldn't have, you're denying your body the very nutrients it should have."

Among the recommendations, the latest guidelines aim to "shift food intake patterns to a more plant-based diet that emphasizes vegetables, cooked dry beans and peas, fruits, whole grains, nuts, and seeds. In addition, increase the intake of seafood and fat-free and low-fat milk and milk products and consume only moderate amounts of lean meats, poultry, and eggs."

[See Best Diets for Healthy Eating .]

When it comes to what kind of plant-based diet one should follow, well, that's where things get complicated. There's not enough evidence to say that a vegan diet, for example, is healthier than eating a mostly plant-based one that includes some meat, experts say. Such distinctions are currently being investigated by Gary Fraser, associate dean of research at California's Loma Linda University, who is leading a study of some 96,000 Seventh-Day Adventists whose diets range from strictly vegan to non-vegetarian. This is the third iteration of the trial, which has linked vegetarian diets to reduced rates of heart attack and diabetes.