When your weight is constant, you are burning approximately the same number of calories as you are taking in. To tip the energy balance toward weight loss, you must either consume fewer calories or burn more calories through physical activity, or both. One pound of body fat represents 3,500 calories. To lose weight at the recommended rate of one-half to one pound per week, you must create a negative energy balance of 1,750 to 3,500 calories per week or 250 to 500 calories per day. To generate your negative energy balance, it's usually best to begin by increasing your activity level while slightly decreasing your calorie consumption.