The Stomach's main function is to 'receive' ingested food and drink and then rot and ripen them by a fermentation process. It then sends the pure portion to the Spleen for its metabolic processes, and the impure part to the Small Intestine for further separation and absorption. Opposite to the Spleen Qi, which ascends to bring Essence to the Lungs and Heart, the Stomach Qi descends to transform food downwards to the Small Intestine. The Stomach is the root of Body Fluids. Therefore it hates to be hot or dry. It prefers Dampness.
Stomach disorders are mainly caused by diet. Foods that are hot, dry, greasy, spicy, or cold disturb the Stomach. Unhealthy eating habits also harm Stomach functions, such as eating while working, driving, or standing, eating irregularly, or over- or under-eating.
The Stomach Qi can be either stagnated or depleted due to excessive worry or thinking. If the Stomach functions are impaired, poor appetite, indigestion, food retention, and distension or pain in the epigastric region can occur.
The Stomach 'receives' food and drink through mouth, pharynx, and esophagus and keep them. This ‘Receiving’ does not only refer to the Stomach's function of receiving ingested food and drink, but it also implies that the Stomach holds these down.
The Stomach's receiving function also plays a role in appetite. A good and healthy appetite shows a strong Stomach ‘receiving’ ability. A poor appetite shows a weak Stomach ‘receiving’ function. A total loses of appetite indicates the complete collapse of the Stomach ‘receiving’ function. Hiccup, nausea, and vomiting also indicate a weak Stomach ‘receiving’.
The Stomach ‘ripens’ and ‘rots’ ingested food and drinks by a fermentation process. It then sends the pure portion to the Spleen for its metabolic processes, and the impure part to the Small Intestine for further separation and absorption. Together with the Spleen, the Stomach is called the origin of Qi and Blood due to its function of transforming food and drink into Essence. They are called the root of "Post Heaven Qi" or Grain Qi (Gu Qi). It is opposed to the "Pre Heaven Qi" inherited from parents at conception.
Together with the Spleen, the Stomach plays an important role in transporting Grain Qi and Essence to the whole body, especially the four Limbs. The Spleen and the Stomach works closely and they are inseparable. If this transportation is damaged, it causes fatigue and weak limbs. The Stomach function of transporting food Essences also impacts the pulse. If Stomach Qi is normal, there is a gentle, flowing, and relatively soft pulse.
The Stomach influences the tongue coating. It is created by the ‘dirty Dampness’ which is a by-product of the Stomach activity of rotting and ripening. A thin white coating reflects a healthy Stomach function. In the case of coating absence, the Stomach's digestion function is impaired and Stomach Qi is weak.
The Spleen Qi ascends to bring Grain Qi and Essence to the Lungs and Heart while Stomach directs transformed food downwards to the Small Intestine. If the Stomach descends Qi properly, the digestion process goes smoothly. If impaired, food stagnates in the Stomach, causing a fullness feeling and distension, sour regurgitation, belching, hiccup, nausea, and vomiting. Finally, Liver Qi helps Stomach Qi descending.
As the opposite of the Spleen, the Stomach hates to be Hot or Dry. It likes Dampness. It is the origin of Body Fluids. The food and drinks ingested are one of the important sources of Body Fluids. If there are sufficient fluids, the Stomach digestion function is smooth and the sense of taste is normal. In the case of Stomach Fluids Deficiency, it causes dry and cracked tongue, poor digestion, and thirst. Eating too late at night is one of the main reasons for Stomach Fluids Deficiency.