Chemicals in food

The intake of food is essential for the efficient production of energy for all living things. Humans are not like plants, which use the carbon dioxide of the air to harness the sun’s energy. We are dependent on the use of plants as food, or other animal material which in turn has already eaten plants. The types of food that are essential for healthy living are mostly carbon-based molecules: carbohydrates, proteins and fats, plus small quantities of minerals and vitamins and water. The effective use of these materials is governed by the interchange of chemical reactions. These are woven into the whole body metabolism. All are geared to give an efficient supply of energy to keep us warm, and for use in growth and cell replacement.

Chemical reactions within cells that can combine simple substances into more complex or larger molecules are called anabolic processes.
These reactions require energy (usually heat) to make the reactions proceed and often involve dehydration (removal of water molecules). Such a reaction is the synthesis of large molecules of food protein from small amino acid molecules. The amino acid units have been formed by breaking down food proteins taken in from other foods that have been eaten.
These chemical reactions that break down foods are called catabolic processes.
These reactions involve hydrolysis (reaction with water) and give out energy.
The fine balance of chemical reactions which release energy (food eaten) and those that require energy (the body and cell-building processes) takes place in the metabolic controllers found in the hypothalamus. The energy transfer agent between these processes involves ATP. Most of the energy produced is lost as heat to the environment. Only part of it is available for cell building, hence the need for regular eating.