Diet and nutrition systems employ varied philosophies to achieve optimal physiology by providing high quality nutrition and healthful physical activity.

Specific nutrients have been used in a "nutraceutical" manner for the treatment of certain diseases.

Examples include folic acid to prevent neural tube defects, heart disease, and low fat diets to reverse coronary heart disease.

In the United States, the primary causes of death are: cardiovascular disease 50%, cancer 25%, lung disease 6%, infectious disease 4%, diabetes 2% (its contribution to cardiovascular disease and syndrome X is not measured), accidents 0.5%, all other about 15%.