The process of digestion is not complete when food passes through the three zones of the gastrointestinal tract. The nutrients that result from prapaka digestion are still not in a form that can be assimilated by the dhatus. Because each dhatu has a different structure and function in the body, it requires its own metabolic process — one that can convert the raw nutrients into a form that can be used for its specific nutritional requirements.
Vipaka, or post-absorptive digestion, begins once the nutrients are absorbed into the body from the area surrounding the ileocecal valve, which lies at the juncture of the small and large intestines. This second phase of digestion continues the process of conversion through a fixed sequence of increasingly refined metabolic processes. Each dhatu has its own digestive or dhatu agni, as distinct from the jathara agni operative in the G-I tract. This agni converts the raw foodstuffs sent to it from the previous stage of digestion into the precise nutrients needed by that dhatu.
Each of the seven dhatus gets nourished in the same order that it develops in the body. Prapaka digestion converts food into a form that can then be acted upon by rasa’s dhatu agni and the doshas. Rasa metabolism, which begins vipaka digestion, produces a substance capable of sustaining rasa dhatu, the nutrient fluid or plasma. Like a pigeon finding edible grains among pieces of gravel, rasa metabolism selects the parts of the processed food-stuff which will nourish it. Kapha binds together whatever is unusable and vata takes it back to the G-I tract for elimination as mala.
Rasa dhatu, however, does not take all nutrients created by its dhatu agni for itself. It takes only that portion which is required for its nourishment. The remainder gets bound up by kapha and transported by vata to rakta dhatus (blood) metabolic staging ground, which is located primarily in the liver and spleen and, to a lesser degree, in the bone marrow. Rakta’s agni now transforms the nutrient fluid of rasa dhatu into a form that is useful for it. Again, vata takes the unusable by-product back to the G-I tract to be discharged as mala. Rakta keeps a portion of the end-product of this metabolic refinement for its own nourishment. The rest goes to the muscles, the seat of mamsa dhatu.
These sorting and transporting mechanisms resemble an irrigation system where water is directed through main and subsidiary channels. Waste products are separated for elimination and the remaining foodstuff continues to the next dhatu for further refining until all the dhatus have been nourished.
Each dosha plays a role in vipaka digestion and works in precise coordination with the other two to accomplish this process. As we have indicated, vata acts as the carrier vehicle. It takes raw material to the next dhatu, separates what is usable and transports both nutrients and waste products to their respective destinations. Pitta’s heat converts nutrients into substances that sustain each of the dhatus. Kapha liquefies and binds the raw food materials, the refined nutrients and the malas so that vata can then transport them.
Vipaka digestion ends when all the physical substances and structures of the body have received sufficient nourishment. Its final stage takes place in shukra dhatu and produces something called ojas. Ojas represents the essence of the entire digestive process and, according to Ayurveda, is the factor responsible for the body’s immunity to disease.
In addition, it is this highly refined biochemical that is responsible for nourishing the non-physical parts of life: the senses, mind and soul. Ojas generates harmony and coordination among the four major aspects of human life and establishes their vital connection with atma or universal consciousness. It allows every cell in the body to function in direct communication with nature’s limitless intelligence. Ultimately, it is this substance that supports the experience of intimate oneness with all of life — enlightenment — the goal of all great spiritual teachings throughout the ages.
Ayurveda places great emphasis on strong, efficient digestion not only because of its vital importance for physical well-being, but also because healthy digestion is vital for connecting the parts of life to their basis in wholeness. Any breakdown in the activities which nourish one dhatu will inevitably weaken the health of all the dhatus in the developmental sequence. Not only is ama produced, but ojas becomes depleted and its vital function for life is lost.
Ayurveda’s most effective treatment for preventing the formation of ama in the first place is education. When we learn how to increase the sattva in our minds, we spontaneously make diet and lifestyle choices that truly nourish us and maintain our health and happiness. These choices then ensure that the doshas maintain a balanced relationship among themselves and metabolism is efficient. The last part of Chapter Five and the whole of Chapter Six describe the things we can do in our daily routine to increase sattva and preserve harmony among the doshas.
However, when ama is already present in the body, Panchakarma, Ayurveda’s science of rejuvenation, provides the primary means to re-create health. Through its time-tested purification procedures, Panchakarma reestablishes balance among the doshas, normalizes digestion and removes the toxic accumulations of ama from the dhatus. It allows the body’s innate healing intelligence to restore the dhatus to their normal functioning. Panchakarma reverses many cases of degenerative diseases and promotes a long and healthy life. However, its ultimate purpose is to restore the harmonizing function of ojas and reestablish our full, conscious connection to universal atma, the source of life.
With the knowledge of digestion, we now have a sufficiently firm foundation in Ayurvedic theory to understand how a single system of health can be both comprehensive enough to include all of life and specific enough to address the uniqueness of every individual human being. The next chapter, entitled Prakruti, is the culmination of Ayurvedic theory. It gives each person the practical understanding of their uniqueness and how they fit into the cosmic web of life.