A Calorie is a unit of energy, not a discrete part of food. An individual's daily requirements can be expressed in terms of kilojoules of energy, but this hides the importance of the various types of energy source and their correct proportions, as well as the role of micro nutrients such as vitamins and minerals. Expendable weight or body bulk is made up mostly of fat which is the method by which the body stores food for a source of available energy. What we need to eat is directly connected with how much we mechanically exercise or use our bodies. Unfortunately, depending upon our inherited genes, we all have a different basic level of resting metabolism.
Some families are lean hungry types and burn up energy just sitting on a seat.
Other families in the same circumstances in the same seat would burn up very little energy. They are the storage types and to them food and overweight is a lifelong problem. In most individuals either regular aerobic exercise or strict dieting are the only answers to a particular problem of weight. Few of us, are lean and hungry and most of us have to earn our kilojoules. What the apparently overweight person with perhaps a lower metabolism should realise is that good health can be associated with a well proportioned figure.