Beyonce covers the April issue of Shape magazine

Bow down, indeed! Beyonce covers the April issue of Shape magazine, and flaunts her own stunningly toned, slim shape in a multi-colored, skintight, wet-suit-like bikini. Inside the issue, the 31-year-old singer, who debuted her new song "Bow Down/I Been On" via her website Sunday, talks about her 57-pound weight gain during her pregnancy with daughter Blue Ivy, 14 months. PHOTOS: Beyonce's body evolution "I didn't have a lot of time to lose the weight because I scheduled a show [in Atlantic City, NJ] three months after I gave birth, which I would never do again!" the Grammy winner admits. Jay-Z's wife got her body back quickly via "a very low-calorie diet," she says. "I stayed away from red meat and ate a lot of fish, replaced pasta and rice with quinoa." PHOTOS: Beyonce's pregnancy with Blue To maintain that enviable bod, she keeps a reasonable diet -- with one very essential cheat day. "I always have breakfast, say, scrambled egg whites, a vegetable smoothie, or whole-grain cereal with low-fat milk," recounts the Grammy winner. "For lunch and dinner, I eat a lot of fish and vegetables. And throughout the day, I try to stay hydrated . . . I always treat myself to one meal on Sundays when I can have whatever I want. Usually it’s pizza, which is my favorite indulgence." PHOTOS: Meet Blue Ivy Carter Beyonce launches her Mrs. Carter Tour in Belgrade, Serbia April 15, and in her latest track, she defends her time away from the spotlight. "I took some time to live my life, but don't think I'm just his little wife," she sings of her hubby, 43. "Don't get it twisted, get it twisted, this my sh-t, bow down b-tches."