BIOLOGY Volume 1 - A Guide to General Biology - 2004

8. HETEROTROPHIC NUTRITION

8.7. Human Nutrition

8.7.8. Proteins

Proteins are primarily essential for growth and repair processes. These compounds perform A wide variety of Functions (Sec. 3.5). If the diet lacks adequate amounts of CARBOHYDRATES and fats, proteins can serve as a source of energy.

Proteins are composed of Amino Acids. Typically, 20 different amino acids make up proteins; much like fats, these Amino acids can be divided into two types — essential and non-essential.

Essential Amino Acids must be obtained through the diet because the body either cannot synthesize them at all or produces them at a rate too slow to meet physiological demands. A deficiency of these amino acids can lead to various health disorders. Eight out of the 20 Amino acids are essential for adults, and 10 for children. Non-essential amino acids can be synthesized within the body from essential ones. Proteins that contain high amounts of essential amino acids are referred to as first-Class or high-quality proteins. These include common animal proteins found in milk and dairy products, meat, fish, and eggs. For vegetarians, soy protein is a recommended source of first-class protein. Other proteins are classified as second-class or low-quality proteins.