Vayu, Agni and water acting as vatha, pitta and kapha is responsible for strong and effective digestion. The metabolic function and its relationship to health is the co-ordinated action of the three doshas.

Doshas and Digestion

The disease process starts when the doshas natural relationship experiences an imbalance and is impaired.When one or more of the doshas becomes excessive or deficient in thier functions, indigestion results.The doshas perform many functions but pitta plays a important part in digestion.

Agni

Pitta dosha controls digestion in the gut and is the energy which gives rise to burning or combustion process. JATARAGINI manifests in the form of pitta, the digestive fire.
Food that is digested well and nourishes the tissues is good and the person enjoys good health and his state of agni is called SAMANAGNI. 

When kapha becomes strong,food is not digested properly.The toungue gets coated due to indigestion and felling ill health.Tierdness and lethargy sets in this state is called MANDAGINI. When pitta is excessive the food gets burnt out instead of being digested properly and the person will be hungry at the same time not able to digest properly leading to peptic ulcer and gastritis.

At times vata goes out of hand.It plays hide and seek ,one day it is strong and one day weak , causes abdominal cramps,colic pain, constipation .This is called VISHAMAGNI .
Generally, if Jataragni is weak all agnis too get vitiated leading to weakness and general slowing of metabolism.

When digestion is impaired, nutrients are not available to nourish the tissues.Toxins accumulate leading to impaired functioning and constitute the root cause of most degenerative disease.

Identifying Food  According to the Doshas

If we wish to have a diet that includes food items of particular doshas, we should be able to identify food based on their qualities.

KAPHA FOODS

Food which increases the water and earth element .These foods are cold,liquid and heavy They nourish the body and add substance to it.Milk,banana and most grains are predominately kapha quality .When grains are grounded into flour it becomes white and tastes sweet, tend to be heavy and increase body weight .Eg if you crush banana it becomes a solid mass and it nourishes the body.

PITTA FOODS

These are brightly coloured ,shiny and much lighter .They have a sour,spicy and pungent flavour. Pepper, turmeric, ginger, garlic, chilly, tamarind etc.When in moderation they improve metabolism, in excess they create too much heat in the body.

VATA FOODS

They exhibit cold, dry, rough, hard and light qualities. Legumes,beans,lentils are dry, crack open and fall out of pods, they provide energy and motility for the body.Eg water melon when we crush it becomes juice, it is a diuretic and dries up the body. If we eat legumes it produces gas in the body.