Vishmagni, Tikshnagni and Mandagni are caused by their doshic predominance respectively (vata, pitta, kapha), while samagni (balanced agni) is caused by the normalcy of all doshas”. Ashtang Samgraha, Ch.1, vs. 24.
Here, we find the three states of agni (digestive fire); variable, high and low. Vata vitiation causes variable agni. Pitta vitiation causes high agni. Kapha vitiation causes low agni. When the doshas are in a healthy state however agni is balanced and healthy. When agni is healthy, digestion works well. When digestion works well, there is no ama (toxicity from digestion) and ojas is formed. Ojas protects the body from disease. Hence, a wise person guards their agni through following a proper diet, by taking food properly, and by following healthy daily and seasonal routines.
About the Image: Agni is so important that it was worshiped as one of the most important ancient Vedic Gods. More hymns were sung to the God Agni in the Vedas than any other God. The God Agni is the source of all fire, even the sun, and the source of all light. In the body, there are many types of agni that regulate metabolism. Agni’s light is the light that illuminates consciousness.