As a tech-obsessed child growing up in the nineties, Rob Rhinehart was always puzzled by food. Here he was, eagerly embracing the wonders of the information era, and he had to gnaw on seared chunks of meat and raw vegetables. “I remember when I was very young, eating lettuce and thinking it was very weird to be eating leaves, sitting in this nice house with all of these electronics around us,” he says now. These days, Rhinehart doesn’t eat much lettuce or anything else recognizable as food. Instead, the 25-year-old gets most of his nutrition from a water bottle filled...