Christine Dougherty, a 27-year-old business consultant in Pensacola, Fla., thinks so. “I don’t like to cook, and I wanted to be realistic without changing my lifestyle too much,” Ms. Dougherty said. She began replacing her usual fast-food lunch or dinner with meals from the Fresco menu at Taco Bell, which consists of seven items — including burritos and tacos — each with less than 9 grams of fat, compared with, say, 30 grams of fat in the Stuft beef burrito on the regular menu.