The human body has thousands of types of proteins, all of which play vitally important functions. While the body produces some of the amino acids it needs, the rest must be supplied through diet. This informative introduction explains what proteins are, the various tasks they enable, their diverse dietary sources, and what can result from consuming too much or too little protein. Sidebar boxes define key vocabulary words or contain questions to spur critical thinking.

Proteins are nutrients -- Amino acids -- Fibrous proteins -- Globular proteins -- Sources of protein -- How much protein do people need? -- Importance of protein -- Malnutrition -- Too much protein -- Essential and useful.