The body's ability to fight off infection depends on its immune system, most noticeably the ability of the immune system to produce a diverse array of defensive proteins known as antibodies. Each antibody is able to bind to specific parts of infectious organisms or other foreign chemicals known collectively as antigens. Once bound to an antigen, an antibody assists in the elimination of the antigen in a variety of ways. Because a specific antibody is required for each specific antigen, the body can produce an astonishing diversity of antibodies, which requires a considerable amount of protein synthesis.

This means that a healthy immune system depends on a good supply of the amino acids needed to synthesize new antibodies. Malnourished young children, particularly in developing countries, are known to have a lowered resistance to infection, which leaves them unable to fight off many infections. This lowered resistance to infection is attributed to an inability to produce adequate supplies of antibodies and other defensive proteins, which can in turn be attributed to a protein deficiency in their diets.

The health of the body is also threatened by various toxic compounds that are found within foods, and in the environment at large. These toxins are normally detoxified by enzymes found mainly in the liver, which convert them into harmless substances. If protein synthesis is restricted because of a nutritional deficiency, the ability of the body to detoxify harmful chemicals can be significantly reduced. This also makes a person with a protein deficiency more susceptible to the effects of poisons or drugs.

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