"I eat a lot of protein and eat pretty clean. Junk food drags you down," Health magazine's May cover girl says. "It's a conscious decision every day to eat something healthy vs. not healthy."
To maintain her shape, the 27-year-old country superstar -- who's engaged to singer Blake Shelton, 34 -- relies on the help of a personal trainer to "keep me in check."
"We can find somewhere to work out anywhere -- we don't have to just be at the gym," the Grammy winner says. "We do a lot of circuit training, lunges and crunches. And every morning we walk for 30 minutes."