So far we have been concerned with foods containing carbohydrates and fats, which produce heat and energy.
Proteins which build tissue and repair worn-out cells, are more complex than either carbohydrates or fats. They consist of carbon, hydrogen, oxygen, nitrogen, and also contain sulfur and phosphorous.
Nitrogen found in proteins is an important element. It makes up four fifths of the atmosphere and is essential to both plant and animal life.
Proteins are built up of simpler substances called amino acids. At least 20 of these amino acids must be present before they may be classed as complete proteins. They will support life. Incomplete proteins, not containing all amino acids, will not.
Good sources of complete proteins are beef, fish, milk, eggs and soy beans. Incomplete proteins are peas, beans, peanuts and some vegetables.
Proteins are not stored in the body in the same way as carbohydrates and fats. Therefore we should be careful to maintain the protein intake at an even level.
Do not overeat protein food. This is wasteful, since proteins cannot be stored in the body.