To maintain a healthy weight, the key is to burn all the calories per day that you consume. To lose weight, you need to burn more than you take in. It’s really that simple. Obviously, the quality of your food will dramatically impact your overall health in time, but fat is stored energy and losing weight in large part is a calories in, calories out equation. So, combined with a good exercise regimen, dropping pounds—or staying slim—depends on monitoring your calorie intake.