It has even entered bodybuilding, perceived by many as a population of vein-popping men and women thriving off meat and artificial enhancements. Competitors like Sitko are forging a distinctive subculture of antibeef beefcakes who hope to change more of their competitors’ eating habits.

As a vegan, Sitko, 29, does not eat meat, dairy or, he said, “anything else that comes from an animal.” As a bodybuilder, he spends hours at the gym lifting barbells, running on a treadmill and sculpturing his 5-foot-11, 180-pound body. Then he spray-tans and parades before a panel of judges in a posing suit, known in the sport as a mankini. He is preparing for a competition in March.

There is little official data on competitive bodybuilders who are vegan, though the Web site veganbodybuilding.com has more than 5,000 registered users.

Denny Kakos, the president of the International Natural Bodybuilding Association, said he had no vegan bodybuilders entering his competitions in the late 1980s and early ’90s. Today, vegans make up a sliver of the approximately 6,000 people who compete through the group each year, but they have been a steady, small presence since the 2000s, Kakos said.