The zang-xiang theory holds that there is a close connection between the internal organs and the physical body. This special relationship constitutes the human body as an organic whole, with the five zang organs and six fu organs housed within, linked externally to the si zhi (four limbs) and jiu qiao (nine orifices).

The liver governs the free flow of qi and blood throughout the body, regulates the emotions, and stores blood. “Its lustre shows in the nails; its fullness in the sinews.” When liver blood is abundant, the nails are firm and lustrous, and the tendons are supple. Its corresponding flavour is sour, its colour is green, and its associated season is spring. In spring, one should follow the ascending and dispersing nature of liver qi and engage in more physical activity.

The heart is the sovereign of mental activities, consciousness and blood circulation among the five zang (viscera). “Its  lustre shows in the face; its fullness in the blood and vessels.” Observing whether the complexion is rosy, whether the blood circulates smoothly, and whether the vessels are well-nourished can reflect the function of the heart. Its corresponding flavour is bitter, its colour is red, and its associated season is summer. The summer heat easily gives rise to fire, and bitter-flavoured foods help to clear heat and nourish the heart.

The spleen governs the transportation and transformation of food and dampness, absorbs the essence of nutrients, and generates qi and blood. It is the pivot of the ascending, descending, floating and sinking movements of qi, and provides the driving force for ascent. “Its lustre shows in the lips; its fullness in the muscles.” The colour of the lips, the presence of lip disorders, and whether the muscles are strong all reflect the function of the spleen. Its corresponding flavour is sweet, its colour is yellow, and its associated season is late summer (the period from late summer to early autumn, or the transitional phases between seasons). If one inexplicably experiences a sweet taste in the mouth, it may be a manifestation of damp-heat in the spleen.

The lung governs breathing and controls the movement of qi. It diffuses upward and outwardand descends, and assists in the regulation of body fluids. “Its lustre shows in the body hair; its fullness in the skin.” Whether the skin and body hair are moist and resilient reflects the function of the lung. Its corresponding flavour is pungent, its colour is white, and its associated season is autumn. In autumn, one should attend to the restraint and nourishment of lung qi, to guard against autumn dryness damaging the lung.

The kidney governs sealing and storage, stores essence (jing) and qi, secures urination and defecation, and is related to the depth of respiration, growth and development, reproduction, and the regulation of body fluids. “Its lustre shows in the hair, its fullness in the bones.” When kidney essence is abundant, the hair is thick and lustrous, and the bones are strong and powerful. Its corresponding flavour is salty, its colour is black, and its associated season is winter. If one inexplicably detects a salty taste in the mouth, it may be appropriate to consider supplementing the kidney.