Or burn more off. Shedding belly fat boils down to a simple equation: Calories in – calories out = total weight loss or gain. “Calories out” is the energy your body spends keeping your heart pumping, doing daily activities, going to the gym, etc. “Calories in” is the sum of every morsel that passes between your lips. To maintain a healthy body weight, a moderately active man needs 2,400 to 2,600 calories per day.