The caveman lifestyle, in Mr. Durant’s interpretation, involves eating large quantities of meat and then fasting between meals to approximate the lean times that his distant ancestors faced between hunts. Vegetables and fruit are fine, but he avoids foods like bread that were unavailable before the invention of agriculture. Mr. Durant believes the human body evolved for a hunter-gatherer lifestyle, and his goal is to wean himself off what he sees as many millenniums of bad habits.

These urban cavemen also choose exercise routines focused on sprinting and jumping, to replicate how a prehistoric person might have fled from a mastodon.

In a city crowded with vegetarian restaurants and yoga studios, the cavemen defy other people’s ideas of healthy living. There is an indisputable macho component to the lifestyle.

“I didn’t want to do some faddish diet that my sister would do,” Mr. Durant said.