But one paper suggested that low-protein diets (associated with vegetarians) reduce calcium absorption and may have a negative impact on skeletal health. And although several studies on Seventh-Day Adventists (typically vegetarians) indicated that they have a longer-than-average life expectancy, other studies found that prostate-cancer rates were high in Adventists, and one study found that Adventists were more likely to suffer hip fractures.

Can it be that vegetarianism is bad for your health? That's a complex issue. There's a big, beautiful plant kingdom out there; you ought to be able to dine healthily on this botanical bounty. With perfect knowledge, you can indeed eat like a king from the vegetable world. But ordinary people are not nutrition professionals. While some vegetarians have the full skinny on how to watch their riboflavin and vitamins D and B12, many more haven't a clue. This is one reason that vegetarians, in a study of overall nutrition, scored significantly lower than nonvegetarians on the USDA's Healthy Eating Index, which compares actual diet with USDA guidelines.

Another reason is that vegans skew the stats, because their strict avoidance of meat, eggs and dairy products can lead to deficiencies in iron, calcium and vitamin B12. "These nutrients are the problem," says Johanna Dwyer, a professor of nutrition and medicine at Tufts University. "At least among the vegans who are also philosophically opposed to fortified foods and/or vitamin and mineral supplements."

Debates about the efficacy of vegetarianism follow us from cradle to wheelchair. In 1998 child-care expert Dr. Benjamin Spock, who became a vegetarian late in life, stoked a stir by recommending that children over the age of 2 be raised as vegans, rejecting even milk and eggs. The American Dietetic Association says it is possible to raise kids as vegans but cautions that special care must be taken with nursing infants (who don't develop properly without the nutrients in mother's milk or fortified formula). Other researchers warn that infants breast-fed by vegans have lower levels of vitamin B12 and DHA (an omega-3 fatty acid), important to vision and growth.

And there is always the chance of vegetarian theory gone madly wrong in practice. A Queens, N.Y., couple were indicted last May for first-degree assault, charged with nearly starving their toddler to death on a strict diet of juices, ground nuts, herbal tea, beans, flaxseed and cod-liver oils. At 16 months, the girl weighed 10 lbs., less than half the normal weight of a child her age. Their lawyer's defense: "They felt that they have their own lifestyle. They're vegetarians." The couple declined to plea-bargain, and are still in jail awaiting trial.

Many children decide on their own to become vegetarians and are declaring their preference at ever more precocious ages; it's often their first act of domestic rebellion. But a youngster is at a disadvantage insisting on a rigorous cuisine before he or she can cook food—or buy it or even read—and when the one whose menu is challenged is the parent: nurturer, disciplinarian and executive chef. Alicia Hurtado of Oak Park, Ill., has been a vegetarian half her life—she's 8 now—and mother Cheryle mostly indulges her daughter's diet. Still, Mom occasionally sneaks a little chicken broth into Alicia's pasta dishes. "When she can read labels," Cheryle says, "I'll be out of luck."

By adolescence, kids can read the labels but often ignore the ingredients. Research shows that calcium intake is often insufficient in American teens. By contrast, lacto-ovo teens usually have abundant calcium intake. For vegans, however, consuming adequate amounts of calcium without the use of fortified foods or supplements is difficult without careful dietary planning. Among vegan youth who do not take supplements, there is reason for concern with respect to iron, calcium, vitamins D and B12, and perhaps also selenium and iodine.

For four years Christina Economos has run the Tufts longitudinal health study on young adults, a comprehensive survey of lifestyle habits among undergraduates. In general, she finds that "kids who were most influenced by family diet and health values are eating healthy vegetarian or low-meat diets. But there is a whole group of students who decide to become vegetarians and do it in a poor way. The ones who do it badly don't know how to navigate in the vegetarian world. They eat more bread, cheese and pastry products and load up on salad dressing. Their saturated-fat intake is no lower than red-meat eaters, and they are more likely to consume inadequate amounts of vitamin B12 and protein. They may think they are healthier because they are some sort of vegetarian and they don't eat red meat, but in fact they may be less healthy."

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