"I'm not a vegetarian," says Marion Nestle, chair of the nutrition department at New York University. "But I eat a largely plant-based diet."
Evidence is mounting that the healthiest diets are loaded with plant foods (vegetables, fruits, beans, and grains) and short on animal foods (meat, fish, poultry, and dairy products), especially fatty ones.
"A diet rich in fruits and vegetables plays a role in reducing the risk of all the major causes of illness and death," says Walter Willett, chair of the nutrition department at the Harvard School of Public Health.
"There's no question that largely vegetarian diets are as healthy as you can get," says Nestle. "The evidence is so strong and overwhelming and produced over such a long period of time that it's no longer debatable."
To many people, "vegetarian" is a loaded word. It typically refers to people who never eat meat, fish, or poultry for ethical, religious, or health reasons. Vegans also avoid all dairy products and eggs.
But scientists are more interested in how often--not whether--people eat animal foods. And much of their research points to the same conclusion: Americans should eat fewer animal foods and more plant foods, especially fruits and vegetables.
Why? Here are ten reasons--some related to health, some not.
1. Cancer. "The science base is very strong that fruits and vegetables are protective for all the gastrointestinal cancers and all the smoking-related cancers," says Tim Byers, professor of preventive medicine at the University of Colorado Health Sciences Center in Denver.
That includes cancers of the lung, colon, stomach, mouth, larynx, esophagus, and bladder. And a recent study found that lycopene--a carotenoid in tomatoes and tomato sauce--may protect against prostate cancer.
It's not clear how fruits and vegetables may cut cancer risk. It could be their phytochemicals--things like carotenoids, vitamins C and E, selenium, indoles, isothiocyanates, flavonoids, phenols, and limonene.
There is also evidence that high-fiber grains like wheat bran can cut cancer risk. "Fiber has a beneficial effect in preventing colon cancer," says David Jenkins, a fiber expert at the University of Toronto.
And pasta, rice, and other grains can replace the animal foods--red meat, in particular--that may increase the risk of some cancers.
"Men who eat red meat as a main dish five or more times a week have four times the risk of colon cancer of men who eat red meat less than once a month," says Edward Giovannucci of Harvard Medical School. Heavy-red-meat eaters were also twice as likely to get prostate cancer in his study of 50,000 male health professionals.
That's just one study. Looking at others, says Lawrence Kushi of the University of Minnesota, "the evidence is quite consistent that red meat is associated with a higher risk of colon--and possibly prostate--cancer."
How red meat may promote tumors is still a question. "For prostate, it's probably related to animal fat," says Willett.
But even lean red meat seems to increase the risk of colon cancer. "It could be the carcinogens created when meat is cooked or meat's highly available iron, or something else in meat," speculates Willett.
2. Heart Disease. "A plant-based diet with lots of fruits and vegetables can reduce the risk of heart disease," says Byers. For the last 20 years, heart experts have emphasized cutting saturated fat and cholesterol, but plants may protect the heart in other ways. Among them:
For example, in a 20-year study of 832 middle-aged men, the risk of stroke was 22 percent lower for every three servings of fruits and vegetables the men ate each day.
Again, no one's sure if it's the potassium, magnesium, fiber, or other components of fruits and vegetables that protect arteries in the brain.
4. Diverticulosis and Constipation. It's no secret that high-fiber grains--especially wheat bran--can help prevent constipation. That's not trivial in a country that spends millions each year on laxatives.
Diverticulosis is also common. An estimated 30 to 40 percent of people over 50 have it, though most have no symptoms. Others experience bleeding, constipation, diarrhea, flatulence, pain, or diverticulitis (that's when the pouches--or diverticula--that form in the walls of the colon get inflamed).
"In our studies, it's clear that fiber both from bran and from fruits and vegetables is protective," says Willett. Men who ate the least fiber (13 grams or less a day) were almost twice as likely to get diverticulosis as men who ate the most fiber (at least 32 grams a day).8
5. Other Diseases. Plant-rich diets may prevent other illnesses:
Any raw food--including fruits or vegetables--can carry harmful bacteria. "For example, recent outbreaks of Salmonella have been associated with cantaloupe, tomatoes, and alfalfa sprouts," says Swerdlow. But meat, seafood, and poultry are the most likely culprits in foodborne illness.
7. The Environment. "Our eating habits have a tremendous effect on the planet," says Jenkins.
Eating animals wouldn't harm the environment if it were done on a much smaller scale, explains Alan Durning, director of Northwest Environment Watch in Seattle.
"Modern meat production involves intensive use--and often misuse--of grain, water, energy, and grazing areas." For example, says Durning:
And the lower price of plants shows up when you eat out. On Chinese, Indian, and most other restaurant menus, the "vegetarian" selections are usually cheaper than the meat, seafood, and poultry.
9. Animal Welfare. It's unpleasant to think about, but before we slaughter them, the animals we eat are often raised and transported under inhumane conditions.
10. Taste. "My number one reason for eating a plant-rich diet is that it tastes good," says Nestle. "I feel deprived if my meal doesn't have lots of vegetables in it."
The five vegetables that Americans eat most are french fries, tomatoes (mostly as sauce or ketchup), onions, iceberg lettuce, and other potatoes, she says. "That's not my idea of fruits and vegetables--that's garnish on burgers."
But if most Americans shrink the meat, seafood, and poultry on their dinner plates, they--or many of their favorite restaurants--wouldn't know what to replace them with.
"You have to go to ethnic restaurants to get interesting plant-based dishes," says Kushi.
It's no coincidence that ethnic restaurants know how to make vegetable dishes taste good. "Fortunately, there's a wealth of experience around the world because almost all traditional diets are plant-based," says Willett.
Yet many Italian, Mexican, and other ethnic restaurants have become so Americanized that their vegetables have been largely replaced by meat and cheese.
And that's a shame. "In Asian and Mediterranean cuisines, cooking fruits and vegetables is an art form," says Nestle.
"The Italians don't put tremendous amounts of meat and cheese on pizza, for example. I had a thin-crust pizza at a traditional restaurant the other day with no cheese--just fresh basil, tomatoes, and garlic. It was totally wonderful."