Nutrition Part III: Protein

Author: Joseph Krachenfels

Protein is chiefly “composed of large combinations of amino acids containing the elements carbon, hydrogen, nitrogen, and oxygen, and is the major source of building materials for muscles, blood, skin, hair, nails, and internal organs” (Mosby’s 1337). Protein is “used by the body to build, repair, and maintain muscle tissue” (Schwarzenegger 670). Once ingested protein is broken down into peptides and amino acids, and currently there are 22 amino acids that have been identified as “vital for proper growth, development, and maintenance of health” (Mosby’s 1337). Of the 22 amino acids, 9 are essential, and therefore must be derived from food sources, while the remaining 13 are non-essential, and can be synthesized by the body, as well as, in being consumed.

Proteins can also be further classified as either complete or incomplete. Complete protein sources such as meat, poultry, fish, eggs, milk, and cheese contain all 9 of the essential amino acids, while protein sources such as nuts and legumes do not, and are considered incomplete. In addition, the amino acid composition of protein sources varies. Eggs are given the highest rating of 100, and used as a standard of comparison when assigning protein ratings to other foods. Below is a list of some common (protein) foods and their respective protein ratings.

Food Source Protein Rating
Eggs 100
Fish 70
Milk 60
Lean Beef 69
Soybeans 47
Dry beans 34
Peanuts 43
Brown Rice 57
White Rice 56
Potato (white) 34

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Arnold Schwarzenegger Encyclopedia of Modern Body Building, Simon & Schuster, 1985.

Mosby’s Medical, Nursing, & Allied Health Dictionary, Mosby, 1998.