Digestion process and causes of indigestion based on Avicenna's view and modern medicine

The process of food digestion is one of the most important physiologic processes in human body. In this review, we are seeking the views of Avicenna, the most distinguished Persian medical scholar about digestion and indigestion. Avicenna's view was based on the humoral theory. Avicenna has focused scrutiny on the process of digestion. He divided this process into four phases including gastric, hepatic, intravascular and intra-organ digestion. A defect in any of these phases can lead to disturbance in other stages. Avicenna approached the problem of indigestion through factors of diet, lifestyle and inherent structural characteristics of digestive organs. Modern medicine confirms Avicenna's opinion about the start of digestion from the mouth, the role of the stomach in digestion and the role of the liver in the metabolism of foods. Overeating or eating certain foods, snacking between meals, eating variety of different foods together, intense physical activity, sexual activity after a meal, stress and sleep insufficiency are among factors that may be linked to indigestion in modern medicine viewpoints and also have been mentioned in Avicenna's teachings. It seems rational to consider the medical approaches recommended by Avicenna for future studies in the field of digestive disorders.