India is considered to be part of South Asia, which is a group of countries bounded by the Indian Ocean in the south and the Himalayas, Karakoram, and Pamir mountains in the north. Indian religion and medicine have rich textual traditions that began more than two millennia ago. Structured lists of bodily constituents, humoral theories of physiology and disease, medicines and prescriptions on healthy living emerge from the scriptures of religious traditions that are now referred to as Hinduism and Buddhism. By the time the earliest Sanskrit medical texts were composed, these rudimentary ideas had developed into sophisticated systems of medicine generally known as Āyurveda, a term which means ‘knowledge (veda) for longevity (āyus)’. Two of the most important works, the Carakasaṃhitā (circa 2nd CE) and Suśrutasaṃhitā (recompiled in 6th CE), document the teachings of longstanding medical traditions that evolved in organised cosmopolitan societies with medical institutions. Some of their ideas anticipate the modern development of hospitals, surgery and the management of epidemics.
In premodern India, the guts were the site of digestion and digestion was conceived as a process of cooking. In fact, the Sanskrit words that are commonly translated as digestion literally mean ‘cooking’ (pācana) or ‘burning’ (dīpana), and the process relies upon the body’s fire (agni), which is located in the abdomen. The cooking begins as the food descends from the stomach, which is called ‘the receptacle of raw food’ (āmāśaya), and finishes in the intestines, ‘the receptacle of cooked food’ (pakvāśaya). The cooking process produces nutrient fluid (rasa) and waste (mala). Nutrient fluid is further transformed by heat in the body to produce six other bodily constituents, namely, blood, flesh, fat, bone, marrow and generative fluid. Bodily winds (prāṇa) of various kinds move the food through the body, fan the fire, distribute nutrient fluid and expel the waste. The cooking of each bodily constituent produces different waste materials, ranging from phlegm and sweat to urine and faeces. If the ratio of waste to nutrient fluid is appropriate, the humours (bile, wind and phlegm) are balanced and health is maintained. If the balance of the humours is lost, disease ensues. An Ayurvedic physician can treat disease by prescribing medicines, diets and other treatments that balance the humours and strengthen the patient’s digestive fire so that the ingested food is properly cooked.