What Is Agni? Ayurveda's Digestive Fire
Agni is the fire of transformation in the body: the power that digests food, separates nourishment from waste, builds each of the seven tissues in turn, and burns off what would otherwise remain as ama, undigested residue. In Ayurveda there is no health without a sound agni and no disease that does not touch it. The Charaka Samhita states that strength, health, life, complexion, and vitality depend on agni, and that when it is extinguished the person dies; that is a paraphrase, and the tradition quotes the sense of it from memory.
The thirteen agnis
The popular account gives four kinds of agni. The classical account gives thirteen, in three groups.
Jatharagni, the fire of the stomach and gut, is the one. It receives food, cooks it through the three stages of digestion, and sets the strength of every other fire. When jatharagni is sound the rest follow; when it fails the rest fail.
The five bhutagnis correspond to the five elements: earth, water, fire, air, and space. After the gut has done its work, each bhutagni transforms the corresponding element in the food into the same element in the body, so that the earth of a grain becomes the earth of flesh. This is the step at which food ceases to be foreign.
The seven dhatvagnis belong to the seven tissues: rasa, the nutrient fluid; rakta, blood; mamsa, muscle; meda, fat; asthi, bone; majja, marrow and nerve; and shukra, the reproductive tissue. Each dhatvagni takes the nourishment passed on from the tissue before it and turns part into its own tissue, part into the tissue's by-products, and part into the fuel for the next. The chain takes time, and the Ashtanga Hridaya's teaching on the tissues is the reason a rasayana is given for weeks and not days.
The four states of jatharagni
Jatharagni has four conditions, and the first task of examination is to place the person in one of them.
Samagni is balanced fire: hunger arrives on time, food digests fully, the stool is formed and without smell, and the person feels light after eating. It belongs to the person whose doshas are in their natural proportion.
Vishamagni is irregular fire, the mark of Vata: hunger that comes and goes, digestion fast one day and slow the next, gas, bloating, and alternating stool. Regular meals, warm and unctuous food, and a settled routine are its treatment before any herb.
Tikshnagni is sharp fire, the mark of Pitta: hunger that cannot wait, food digested too fast, burning, thirst, loose stool, and anger when a meal is late. It is calmed with sweet, bitter, and cooling food and by never skipping meals.
Mandagni is dull fire, the mark of Kapha: little hunger, heaviness after eating, sluggishness, a coated tongue, and the slow accumulation of ama. Of the four it is the one the texts treat as the root of most disease, and it is answered with light food, fasting, and the pungent and bitter tastes that kindle fire.
The three stages of digestion
Within a single meal, jatharagni works through avasthapaka, three phases each governed by a dosha. In the stomach the food is sweet and Kapha rules, which is why heaviness after eating is normal for a time. In the small intestine the food turns sour and Pitta rules; here the real cooking is done and the nutrient is separated from waste. In the colon the residue turns pungent and Vata rules, absorbing what remains and forming the stool. Disorders can be placed by stage: nausea and heaviness are early, burning and sourness are middle, gas and constipation are late.
Agni in treatment
Every Ayurvedic treatment begins by protecting or restoring agni. Deepana substances kindle the fire; pachana substances digest what the fire has left undone. The pungent taste, dried ginger, long pepper, black pepper, and Chitraka, Plumbago zeylanica, are the classical deepana-pachana plants. The rules of eating serve the same end: eat only when hungry, sit to eat, eat to two-thirds of capacity, take warm water rather than cold, do not eat until the previous meal is digested, and take the heaviest meal at midday when jatharagni, like the sun, is strongest. Panchakarma is not begun until agni has been prepared with deepana and pachana, and the graded diet that follows it exists to rekindle the fire that purification has quieted. Chinese medicine's Spleen and Stomach qi is the nearest cousin to jatharagni, and the two traditions give nearly the same advice about warm food and regular hours.