| Food provides an organism with sources of energy and with materials for building up, or renewing, body structures.
|
| The eaten food enters the gastrointestinal (GI) tract. The GI tract together with the organs functionally associated with it, the liver and the pancreas, are responsible for the process of digestion and absorption. Digestion is the degradation of nutrient molecules into components simple enough to be subsequently absorbed in the intestine. Absorption is the uptake of digested components by the intestinal cells (enterocytes). Digestion and absorption of nutrients are closely linked. Digestion is regulated by the nervous system, several hormones, and various paracrine factors. The physical presence of food particles in the GI tract also stimulates the process.
|
| The main classes of macromolecules contained in food are carbohydrates, lipids, and proteins
|
| Carbohydrates and lipids function primarily as sources of energy (metabolic fuels) but also have a nonfuel function in the body. Protein, on the other hand, is primarily used for nonfuel purposes but can, under certain circumstances, serve as an energy source. The composition of foods varies in the proportions of protein, carbohydrate, and fats. In addition, some ingested materials, particularly some complex carbohydrates of plant origin, are indigestible and constitute what is termed 'fiber'.
|
|
