According to ayurveda, there are four possible stages of agni, reflecting our constitutional makeup and its vagrancies. These are sama(balanced metabolism), vishama( irregular metabolism), tikshna( hypermetabolism) and manda( slow metabolism). To understand these different states of digestion requires an understanding of the doshas. Simply put, doshas are constitutional humors composed of the five great elements. They manifest as force movement, of transformation and stability. Their vagrancies reflect excessive movement, excessive heat and excessive mucos secretions.
Vata, the first dosha, is composed of elements of the space and air and will give rise to vishama an erratic digestion, with the peristaltic movement being unpredictable, creating irregularity in appetite, variability in digestion, abdominal distention, indigestion, gases and constipation.
Pitta, composed mainly of fire and some water, is the dosha that creates tikshana agni when out of balance. Because of its hot, sharp, fire like qualities it causes an excessive release of acids and enzymes and thus a desire for large quantities of food. Its liquid, sour and hot qualities can then cause hyper acidity, gastritis, heartburn and diarrhea and eventually lead to ulcers or colitis.