Agni (which means Fire) in Ayurveda is the entity that is responsible for all digestive processes. It’s also called the Digestive Fire, which simplified could be equated with metabolism.
Agni is one of the Five Elements recognized in Ayurveda called Pancha Bhoota, which are defined as Akasha (ether, space), Vayu (air), Agni (fire) or Tejas, Apas (water), and Prthivi (earth).
The function of Agni includes digestion, absorption, and assimilation. For instance, Agni enables the conversion of food into the various Dhatus (plasma, blood, muscle, bone, fat, and reproductive fluids), and thus finally creates energy and vital force.
Agni also relates to emotional digestion. When Agni is strong, we are able to digest and assimilate not only our food, but also our thoughts, actions, and emotions. When Agni is weak, we are not able to digest what we take in and can become physically or emotionally weak or ill.