Physiologists tell us that approximately 3500 calories equal one pound of fat. It doesn’t matter what type of food is eaten-nutritious food or “junk”-it all contains calories, and they all count So if 100 calories remain unburned at the end of each day for 35 days, the body will gain one pound of fat. By the end of the year, the body, will have gained 10 pound at the rate. This is the cumulative nature of weight gain.