Being the biological fire that governs metabolism, agni encompasses all the changes in the body and mind from the dense to the more subtle. Such changes include the digestion and absorption of food, cellular transformations, assimilation of sensory perceptions and mental and emotional experiences. Agni therefore covers whole sequences of chemical interactions and changes in the body and mind. Digestive abilities being related to the strength of agni.
Agni and pitta are closely connected. While both are hot and light, agni is subtle and dry. The heat energy to help digestion contained by pitta is agni. Pitta is therefore the container and agni the content. Agni is acidic in nature and stimulates digestion. It is subtly related to the movement of vata. In every tissue and cell agni is present and is necessary for maintaining the nutrition and auto-immune mechanism. By destroying micro-organisms, foreign bacteria and toxins in the stomach and the intestines.
A balanced agni therefore is vital for health. The strength of the body to resist disease and also its physical strength are directly related to its heat energy determining the metabolic processes of the body. Disturbances to Agni are usually the chief causes of disease.
As per Ayurveda there are thirteen types of Agni in the body and mind according to the conversion and the transformation made. The most important of them is the Jatharagni, the gastric fire, responsible for digesting food eaten by correlating hydrochloric acid in the stomach and the digestive enzymes and juices secreted into the stomach, duodenum and the small intestines. If digestive agni is low and the capacity is impaired, one may experience pain, discomfort, feeling of heaviness or gases gurgling, constipation or loose stools.