The body needs some fat to burn energy and provide a back-up energy source when the body is without food for a long period of time. Fat aids in the absorption of nutrients and provides insulation from the heat and cold. Too much body fat can lead to being overweight or obese. According to the National Heart, Blood and Lung Institute, obesity can cause sleep apnea, type 2 diabetes and gallstones. It can also cause irregular menstrual periods and female infertility. Being overweight puts a strain on the joints and wears away the cartilage between the joints, causing joint pain. Being overweight also increases your risk of certain cancers like gallbladder, breast and colon cancer.