The Stomach's main function is to 'receive' ingested food and drinks and then rot and ripen them via a fermentation process. It then sends the pure portion to the Spleen to be transformed and transported, and the impure part to the Small Intestine for further separation and absorption. In opposition to the Spleen Qi, which ascends to bring food essences to the Lungs and Heart, the Stomach Qi descends to send food downwards to the Small Intestine.
Stomach disorders are mainly caused by diet. Food that are too 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- and 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, distension or pain in the epigastric region can occur.
The Stomach 'receives' food and drink through the mouth, pharynx, and esophagus and keeps them. This ‘receiving’ does not only refer to the Stomach's function of receiving ingested food and drinks, 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 loss 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 via 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 drinks into essences. 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 food essences to the whole body, especially the four Limbs. The Spleen and the Stomach work closely together 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. The coating is created by the ‘dirty Dampness’ which is a by-product of the Stomach's activity of rotting and ripening. A thin white coating reflects a healthy Stomach function. An absence of coating means that the Stomach's digestive 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.
As opposed to the Spleen, the Stomach hates to be Hot or Dry. It likes Dampness since it is the origin of Body Fluids. The food and drinks ingested are one of the important sources of Body Fluids. If the Fluids are sufficient, the Stomach digestive function is smooth and the sense of taste is normal. In case of Stomach Fluids Deficiency, patients will have dry and cracked tongue, poor digestion, and a feeling of thirst. Eating too late at night is one of the main reasons for Stomach Fluids Deficiency.