The issue of sexism in vegan circles is “extremely polarizing,” said Bob Torres, an author of “Vegan Freak,” a guide to living a vegan lifestyle, which generally means avoiding the use of animals for food, clothing or other purposes. Mr. Torres, like many vegans, disavows the “essential idea at the heart of some animal rights activism that any means justifies the ends,” he said. Certain activists, he added, care only about “animal suffering and ignore the suffering of humans,” a category into which he would put women who are exploited.

According to a 2006 Harris poll commissioned by the Vegetarian Resource Group, which publishes The Vegetarian Journal, only about 2.3 percent of the adult population of the United States is vegetarian. At most, half of those are practicing vegans. But the vegan philosophy has achieved a prominence greater than those small numbers would indicate. There are many celebrity acolytes, including Natalie Portman, who recently introduced a line of nonleather shoes. The best-selling diet book “Skinny Bitch” and a follow-up cookbook, “Skinny Bitch in the Kitch,” promote veganism. Both have been accused of sexist undertones.

People adopt a diet free of animal products for a variety of reasons. They may believe it is healthier or more environmentally friendly. They may support animal rights. In addition, veganism is often part of a larger progressive agenda, which makes many particularly sensitive to sexism charges.

Carol J. Adams, the author of “The Sexual Politics of Meat,” a bible of the vegan community, said that women’s rights and the rights of animals have often been aligned. She traces the relationship to the 1890s. “A lot of feminist suffragists also became vegetarian,” said Ms. Adams, who gave up meat in 1974 while living in a feminist community in Cambridge, Mass. She noted that Susan B. Anthony attended a dinner at which the toast was for “Total Abstinence, Women’s Rights and Vegetarianism.” (An unrepentant omnivore, Ms. Anthony had a predilection for porterhouse steak.)

Ms. Adams added that feminists were early adopters of vegetarianism. “Back in the ’70s, lots of women were saying, ‘I don’t want to be a piece of meat. I’m not going to eat a piece of meat,’ ” she said.

Vegans who use sexuality to promote the cause say it is a good way to convert carnivores  in particular, men. Sky Valencia, the founder of the Vegan Vixens, said her group targets “the people who buy Playboy and Maxim and watch talk shows like Jerry Springer. Those are the people we want to educate because they don’t know anything about the environment or animal rights issues or health.”