Wikimedia Commons Over two thousand years ago, there was a man who could walk on water and heal the sick. He was a man of inner serenity and great wisdom; he was even said to have died and then reincarnated. His name was Pythagoras.

Kids today learn about Pythagoras in school because of his theorem on right-angeled triangles: you may still recall the equation a² + b² = c². Pythagoras was also the first to suggest that Earth is round and that the light of the moon is reflected.

But there was more to his life's work than math and astronomy—although walking on water was likely not among his real achievements, just the stuff of legends. People said Pythagoras looked striking: He was very tall and handsome. "God-like," some said. There was even a rumor that he was actually the son of Apollo and the grandson of Zeus himself. What also made him stand out was the way he dressed: he wore white robes and pants, an unusual style, since practically no one in Greece of the sixth century BCE dressed in trousers.

Yet his looks and his choice of fashion were not the reason why he became something of an outsider and a laughingstock for many comedy writers. The reason—or at least one of them—was his diet.

If you lived in Paris circa 1650 or in London in the 1830s, and you decided to stop eating meat, you wouldn't tell your friends you were going vegetarian. You would probably tell them that you were going Pythagorean. Until the word vegetarian got coined in the nineteenth century, it was Pythagoras's name that was used to describe a diet that excluded animal flesh.

Pythagoras believed in metempsychosis, the transmigration of souls. In one lifetime you could be born a human, but in your next you could well end up as a pig and get slaughtered for bacon. According to one story, Pythagoras once stopped beating a dog because he was convinced that in the yelps on the animal he recognized the voice of a dear friend.

If souls did truly migrate from humans to animals, how could anyone touch meat? What if the steak on your plate was made of your great-grandmother? To avoid such risks, Pythagoras and his disciples lived on a simple diet of bread, honey, and vegetables, a diet he also believed to be healthier than a meat-based one (as modern science shows, he was probably right). For Pythagoras, as for most vegetarians until quite recently, going off meat had little to do with animal welfare. It was not about them, the other creatures. It was all about us, humans, and how being cruel impacts our psyche.

As smart as he was, Pythagoras didn't come up with his dietary ideas all by himself. He was quite likely influenced by the priests of ancient Egypt, where the concept of voluntary rejection of meat was already known five thousand years ago. There might also have been some exchange of thoughts between Pythagoras and his famed contemporaries: Buddha and Mahavira (the reformer of Jainism). It appears as too much of a coincidence that the lives of these great philosophers overlapped and that their teachings were so in tune. But even though they all believed in the transmigration of souls and preached abstention from animal flesh, Buddha and Mahavira managed to change Asia, while Pythagoras and his students remained the subjects of ridicule.

So why has meat eating endured in Greece? Did vegetarianism fail there because Pythagoras was not associated with a religion like Buddhis or Jainism? Maybe. It also likely failed because in ancient Greece meat was usually consumed at public festivals that cemented the society and saying no to sacrificial flesh made Pythagoreans outcasts: to reject meat was to reject the whole system of the polis. Meat eating also likely endured in Greece because there was no powerful vegetarian emperor there who would support the meatless movement the way India's famed ruler, Asoka, supported the teachings of Buddha.

What's more, in the times of Pythagoras, meat was prized in Greece as the food to fuel Herculean muscles and boost the performance of beloved athletes—some of whom were quite carnivorous. The wrestler Milo of Croton, for example, was famed for consuming as much as twenty pounds of meat per day. The ancient Greeks, just like Paul Rozin's students at the University of Pennsylvania, believed that "you are what you eat." They thought that consuming the flesh of a nightingale was a recipe for insomnia and would likely conclude that eating boars would make an athlete strong. But what was probably of particular importance to the Greeks' ongoing love affair with meat was that the vegetarian foods of the ancient Mediterranean were not as tempting to the senses as those served in India, with all their spices, vegetables, and fruits. Followers of Pythagoras were known to subsist on little but bread, water, and a dash of wine, while in India vegetables stewed with spices were served on scented rice, follow by dishes of flavored curd, saffron caramel, and sweet cakes with pomegranates and mangoes.

Despite Pythagora's teachings, meat eating prevailed in Greece, and for the rest of antiquity, vegetarianism in Europe was but an elitist philosophy, a domain of outsiders. In the Rome of gladiators, vegetarianism was for radicals, for people who rejected the status quo. If you wanted to stay out of trouble, it was better to hide your veggie ideology behind a slab of meat on your plate. That's what Seneca did, and the poet Ovid. Just to be safe.

Excerpted from MEATHOOKED: The History and Science of Our 2.5-Million-Year Obsession with Meat by Marta Zaraska. Available from Basic Books, a member of The Perseus Books Group. Copyright © 2016.