"People regard food as Heaven." Food is of prime importance for human existence and provides essential nutrients for the growth, development and various physiological activities of the human body to maintain the normal human vital activities. Foods are various and the nutrients are different from one another. On the other hand, the nutrients constituting the human body and maintaining the metabolism of the human body are very various. These nutrients should be obtained from numerous foods while one type or several types of foods cannot possibly contain all these nutrients. Besides, there exists the requirement of a reasonable proportion among various nutrients essential to the human body. If the content of a certain substance is excessive or scanty in the human body, this may influence the absorption and actions of other substances. Accordingly, scientific feeding and reasonable proportions should be advocated in diet in order to make the nutrients in various foods supplement mutually. The advocation of eating various foods, alternative dietary methods and complete diet has the great guiding significance for TCM life cultivation and rehabilitation.
Foods mainly include five flavors, sour, bitter, sweet, pungent and salty as well as four natures of cold, hot, warm and cool. Foods of different natures and flavors vary from one another in their actions. So, food preference inevitably gives rise to diseases or is not beneficial to the treatment of and recovery from diseases if it lasts long. For instance, the patients with yin deficiency or diseases due to yin deficiency should select sweet and moist-natured foods or sweet and cool-natured food to nourish yin and clear away heat. If they eat or addict to warm-natured tonic foods, this not only makes it difficult to restore the balance among qi, blood, yin and yang, but also promotes the internal generation of heat to further consume yin and essence and aggravate the original state of diseases; on the contrary, the patients with yang deficiency or diseases due to yang deficiency should select sweet, warm-natured and tonic food while addiction to cold-and cool-natured foods unavoidably makes yang deficient and cold even more severe, and the diseases worsened. The same is true of flavor preference. For example, overeating pungent foods may cause fire to consume yin; overeating sweet foods may stagnate the functional activities of qi; overeating salty foods may injure the bone and consume qi; overeating bitter foods may dry and consume gastric fluid; overeating sour and astringent foods may make the liver qi stagnated and the spleen qi consumed, etc. Therefore, TCM has been advocating "the balance of the five flavors”since ancient times. Only by balancing the five flavors can the human body take in nutrients in an all-round way and health be enhanced. This is beneficial to the treatment of diseases and the rehabilitation of the body.