Evidence is mounting that the healthiest diets are loaded with plant foods (vegetables, fruits and beans) and short on animal foods (meat, fish, poultry and dairy products), especially those with a high fat content.
"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 Willet, Head of the Nutrition Department at the Harvard School of Public Health.
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: people should eat fewer animal foods and more plant foods, especially fruits and vegetables. Why? Here are 10 reasons - some related to health, some not.
"The scientific base is very strong suggesting that fruits and vegetables are protective elements for all gastrointestinal cancers and all 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 reduce cancer risk. It could be their phytochemicals - things like carotenoids, vitamins C and E, selenium, indoles, flavonoids, phenols and limonene.
There is also evidence that high-fibre grains like wheat bran can reduce cancer risk. "Fibre has a beneficial effect in preventing colon cancer," says David Jenkins, a fibre 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 risks 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 meats 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 - possibly prostate - cancer".
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.
A plant-based diet with lots of fruits and vegetables can reduce the risk of heart disease. For the last 20 years, heart experts have emphasised cutting saturated fat and cholesterol intake, but plants may protect the heart in other ways. Among them:
* Soluble Fibre: "To reduce your risk of heart disease, you may want to eat more beans, peas, oats, and barley," says Jenkins, because their "sticky" soluble fibre seems to help lower blood cholesterol.
* Folic Acid: "The evidence that folic acid reduces the risk of heart disease is pretty strong," says Willet. Folic acid, a B-vitamin, lowers blood levels of a harmful amino acid called homocysteine. "And fruits and vegetables are a major source of folic acid," he adds.
* Antioxidants: a growing body of evidence suggests that LDL ("bad") cholesterol damages arteries only when it has been oxidised (combined with oxygen). That's why researchers believe that antioxidants like vitamin E may protect the heart. And many of the phytochemicals in fruits and vegetables are antioxidants.
* Squeezing Out Saturates: if you eat lots of plant foods, there's simply less room for the saturated animal fats that clog arteries.
There's a lot of evidence showing that fruits and vegetables are beneficial for reducing the risk of stroke," says Willet. For example, in a 20-year study of 832 middle-aged men, the risk of stroke was 22 per cent 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, fibre or other components of fruits and vegetables that prevent arteries from clogging in the brain.
4. Diverticulosis & Constipation
High-fibre grains - especially wheat bran - can help prevent constipation. That's not trivial in a country like the US that spends millions a year on laxatives.
Diverticulosis is also common. About 30 to 40 per cent 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 fibre both from bran and from fruits and vegetables is protective," says Willet. Men who ate the least fibre (13 grams or less a day) were almost twice as likely to get diverticulosis as men who ate the most fibre (at least 32 grams of fibre a day).
5. Other diseases
Plant-rich diets may prevent other illnesses:
* Macular Degeneration: a carotenoid called lutein - which is found mostly in leafy greens - may help prevent the deterioration of the retina that causes blindness in older people. "In our study, people who ate spinach or collard greens two to four times a week had half the estimated risk of macular degeneration compared with those who ate them less than once a month," says Johanna Seddon of Harvard Medical School.
* Neural Tube Defects: folic acid supplements can reduce the risk of spina bifida and other neural tube birth defects. Folic acid from foods (mostly fruits and vegetables) may also cut the risk.
* Diabetes: "We found a lower risk of adult-onset diabetes in people who ate more whole grains," says Willet.
6. Safer food
Some of the deadliest food-borne illnesses enter the body via animal foods. "Ground beef is the most likely source of E. Coli 0157:H7. Poultry carry Salmonella and Campylobacter, and the consumption of raw shellfish has caused infection with Vibrio vulnificus," says David Swerdlow of the Centers for Disease Control in Atlanta.
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 food-borne illness.
"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 North-west Environment Watch in Seattle.
"Modern meat production involves intensive use - and often misuse - of grain, water, energy and grazing areas," says Durning. He cites the following examples:
* Water pollution: the manure and sewage from stockyards, chicken factories, and other feeding facilities can pollute water supplies.
* Air pollution: thirty million tons of methane - a gas that contributes to global warning - comes from manure in sewage ponds or heaps.
* Soil erosion: nearly 40 per cent of the world's - and more than 70 per cent of US - grain production is fed to livestock. For each pound of meat, poultry, eggs and milk we produce, farm fields lose about five pounds of topsoil.
* Water depletion: an estimated half of the grain and hay that's fed to beef cattle is grown on irrigated land. It takes about 390 gallons of water to produce a pound of beef.
* Energy Use: it takes almost ten times more energy to produce and transport livestock than vegetables.
* Overgrazing: about 10 per cent of the arid West of the US has been turned into a desert by livestock. But some of that land couldn't be used for much else. "That's why my argument isn't for vegetarianism, but for people to reduce the consumption of animal products," maintains Durning.
Sure, you can spend $7.99 a pound on mesclun or other gourmet foods. But from squash to sweet potatoes, most plants are a downright bargain. 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.
It's unpleasant to think about, but before we slaughter them, the animals we eat are often raised and transported under inhumane conditions.
The number-one reason for eating a plant-rich diet is that it tastes good. The five vegetables that Americans eat most are French fries, tomatoes (mostly as sauce or ketchup), onions, iceberg lettuce, and other potatoes.
But if most Americans shrink the meat, seafood and poultry on their dinner plates, they - or many of their favourite restaurants - wouldn't know what to replace them with. You have to go to ethnic restaurants to get interesting plant-based dishes. 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 Willet.
Yet many Italian, Mexican and other ethnic restaurants have become so Americanised 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. 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 recently with no cheese - just fresh basil, tomatoes and garlic. It was totally wonderful.