When you eat, you are taking in energy and when you work you are burning energy. When you burn exactly what you take in, you are in a state of energy balance. Energy balance is simply when energy intake is equal to energy expenditure.
But do you eat more than you burn? Or burn more than you can consume? Then your energy balance leaves much to be desired. When your energy intake is equal to the needs of your body, bodyweight is maintained at a fairly constant level. This constant body weight is an index of energy balance in healthy adults.
However, when intake is consistently inadequate and is unable to meet the body’s need for energy, the fat reserves in the body make up for this deficit leading to a loss of weight. An underweight person has reduced the capacity for work, low vitality and low resistance to disease.
