The principles of the Flat Belly Diet are simple: Have four 400-calorie meals a day (including one snack you can consume in the morning or afternoon), eat every 4 hours and include a serving of monounsaturated fatty acids (MUFAs) at each meal to fight belly fat. (Not sure which foods have MUFAs? Check out Flat Belly Diet Foods That Reduce Belly Fat.) Here, we've included the correct portion of a MUFA (in boldface) with every 5-minute meal—and because these dishes are calorie-controlled, they're interchangeable. For example, you may want to try a smoothie diet for breakfast or lunch—it's up to you!