Yin-yang is a generalization of the opposite sides of some interrelated things and phenomena in nature, which includes the concept of unity of opposites. Yin He not only represents opposing things, but also can be used to analyze two aspects of internal opposition. Everything that is vigorous, extroverted, rising, warm and bright belongs to Yang; Relatively static, introverted, healthy, cold and gloomy all belong to Yin. "Yang qi, Yin forming." The yin and yang attributes of things are not absolute, but relative. The growth and decline of yin and yang are mutually restricted, rooted and utilized, and can be transformed into each other under certain conditions. Traditional Chinese medicine believes that the up and down, inside and outside, inside and outside, front and back, and the internal organs of the human body all contain the relationship of unity of opposites of Yin and Yang. The physiological function of human body is also the result of harmony between yin and yang. If yin and yang have advantages and disadvantages for some reason, the body will show a pathological process. Because the internal cause of the occurrence and development of diseases is the imbalance of yin and yang, any disease, although its clinical manifestations are complex and changeable, can be summarized by yin and yang. The fundamental principle of treating diseases is to adjust yin and yang and restore relative balance.

It is not difficult to see that mastering the changing law of yin and yang, carrying out diet activities around regulating yin and yang, and keeping the body "secret of yin and yang" are the core of traditional nutrition theory. Dietary health care, treatment and rehabilitation measures are also established under the guidance of the basic principles of regulating yin and yang.