Weight control is the process of maintaining a healthhy bodyy weight. In human beings, weight control usually involves regulating body fat. When people gain excess weight, most of the extra weight is body fat, and when people lose weight, most of the weight that is lost comes from body fat. The relationship between the amount of energy you obtain through food and the energy your body uses to maintain normal functions and to perform physical activity mainly determines how much body fat you will have.

Weight control is medically important because excess body fat is a major factor in many health problems. The condition of having an excessive amount of body fat is called obesity. Obese people have a higher risk of developing diabetes, hypertension (high blood pressure), and heart disease.

Energy supplied in food and burned by our bodies is measured in units called kilocalories. This term is often shortened to calories. Countries that use the metric system measure energy in joules instead of calories. One kilocalorie equals 4.184 joules. If you eat more calories than your body burns, most of the excess calories will be stored in your body as fat. If you eat fewer calories than your body burns, your body will burn stored fat for energy. For example, eating about 3,500 more calories than are burned will cause you to gain about 1 pound (0.45 kilogram) of fat. You will lose about 1 pound of fat if you consume 3,500 fewer calories than you use.