In Chinese medicine, what is referred to in the West as irritable bowel syndrome is mostly categorized as xie tong, painful diarrhea. If this is accompanied by abdominal distention, this is categorized as fu zhang, while constipation is bian bi. The modern Chinese medical literature is unanimous in saying that the root cause of IBS is always a disharmony between the liver and spleen. Due to emotional stress and frustration, the liver may become depressed and the qi become stagnant. Qi stagnation then results in abdominal distention and pain. Due to worry, lack of exercise, over-fatigue, improper diet, or over or prolonged use of antibiotics, the spleen may become vacuous and weak. Spleen qi vacuity results in fatigue, lack of strength, and downward diarrhea. In addition, these two disease mechanism mutually engender each other. When the liver becomes depressed, it commonly counterflows horizontally to attack the spleen, thus causing or worsening spleen vacuity weakness. Conversely, if the spleen is vacuous and weak, this may cause or worsen liver depression. This is because weakness of the spleen qi may lead to blood vacuity or insufficiency, and the liver can only function when it receives an adequate supply of blood to nourish it. Hence, liver depression, qi stagnation, and spleen vacuity weakness typically go hand in hand in clinical practice. In addition, because of their monthly loss of blood, women’s spleens must work harder at producing blood than men’s spleens must. This also predisposes women in particular to spleen vacuity and explains why three times as many women as men suffer from IBS.

If the liver becomes depressed and the qi becomes stagnant, this stagnation may eventually transform into depressive heat. Over time, this pathological heat will damage and consume the blood, body fluids, and ultimately kidney yin. Spleen vacuity may also lead to blood and, therefore, yin vacuity because the spleen is the root of blood engenderment and the blood and essence share a common source. Since yin is supposed to control yang, if kidney yin becomes vacuous and weak, liver yang may become hyperactive. Since fire burns upward and the heart and lungs are located above the liver, this pathological heat may also accumulate in the heart and/or lungs, disturbing either or both heart and lung function.