Ayurveda is the oldest science of life. Ayurveda links the universe and body as the same. It says that the body is made of Panchamahabhutas (earth, air, fire, water, space); similar to the universe. There are many processes going on within the body and thus, the body loses some elements from the same. So, to replace the eliminated element, one consumes Ahara (food). Agni and food are primal requirements for one’s digestion and metabolic processes. Agni within the body acts in 13 different forms.

To know how our body undergoes digestion, it’s necessary to know the role of Agni in digestion. The ingested food which contains all the elements is first digested by Amashaya (stomach) by the action of Jatharagni. In this stage, specific elements get metabolized by specific Agni. All five Panchamahabhutas get metabolized by Bhutagni and the formation of tissues is brought in by Dhatwagnis. After this metabolic process, the ingested food gets formed into two parts – Prasada (pure) and Mala (excreta). The Doshas and Dhatus are nourished by Prasada and Mala is ejected from the body.

In addition, to understand the process of digestion, it’s also necessary to understand the role of Pitta and Agni in the body. The main function of Agni is to break down or disintegrate the food in its simplest components for further absorption. The functions of Dahana and Pachana in biological terms are performed by enzymes. Agni is located in Pithashaya. The internal secretions are termed Pachak Pitta and secretions by mucosal glands correspond to Grahani.

Amongst the 13 Agnis, Jatharagni plays a major role and is responsible for health, disease, longevity, complexion, strength, luster, immunity, and other vital functions. Aahara provides nourishment, Ojas provides energy and strength, and Agni provides soluble nutrients that can be easily absorbed by tissues.

Process of Digestion:

Prana Vayu (a type of Vata Dosha) is responsible for swallowing and with its power, good is ingested into Kostha (alimentary tract). The food in the alimentary tract gets softened by an unctuous substance and later it splits into small particles by liquid (saliva). The Agni which is located in the stomach is stimulated by Samana Vayu (a type of Vata Dosha, which performs the function of the division of food). The Agni then helps in the digestion of food in the stomach and produces Rasa (chyle) and Mala (wastes). At this stage, Food gets converted into Amashaya and Pakwasaya by the action of Jatharagni. The digestion involves two phases:

1.Prapaka – Pratham Paka (first change)

2. Vipaka – A change that food has already undergone.

Prapaka is divided into three phases:

1.Madhura Avastha Paka

2.Amla Avastha Paka

3.Katu Avastha Paka

Prapaka is acted by Jatharagni to undergo further changes. Prapaka stage starts from the time when the food is introduced into the mouth. The process of fragmentation of food into smaller pieces commences in mouth, by the influence of Bodhaka Kapha (a type of Kapha Dosha). The digestion here is initiated by salivary secretions where insoluble starch polysaccharides are converted into soluble dextrin. The final product form here is known as Madhura.

Then Madhura is ingested from mouth to stomach by the influence of Prana Vayu. Madhura Bhava is acted by hydrochloric acid which is secreted by the mucous membrane of the stomach. This marks the commencement of Amalabhava (the acidic phase of Prapaka). This
process involves conversion of insoluble proteins to soluble ones by the action of enzyme pepsin in presence of HCl. The digestion of fats, proteins and carbohydrates is brought in by Accha Pitta which includes gallbladder, bile, and pancreatic secretions.

The third stage of the digestion is spoken in terms of Katubhava. This is related to the acrid and pungent nature of reaction that occurs in the large intestine. When the ingested material is passed from Amashaya to Pakwasaya, it gets dehydrated and gets converted into lumps due to heat and during this phase, it produces acrid and pungent gas. In Ayurveda, the formation of lumps due to heat is termed as Pari pindita Pakwasaya and formation of pungent gas is termed as Vayusyat Katubhavatah. This acrid gas contains odour of iodole, phenol, hydrogen sulphide and ammonia.

Vipaka – Post digestive effect:

Post digestive effect is classified into three phases. Vipaka is dependent on the quality of food ingested. The ultimate change in Rasa that has occurred to initially ingested food, due to the action of Jatharagni, is known as Vipaka. The six Rasas yield three types of Vipaka – Madhura and Lavana Rasa to Madhura Vipaka (sweet); Amla Rasa to Amla Vipaka (sour) and Katu, Tikta, Kasaya Rasa to Katu Vipaka (pungent).

Secondary Digestion:

It is also known as tissue metabolism. In this phase, metabolism takes place in each tissue channel of the specific tissues. Due to this, each tissue is formed in each channel. Ranjaka Pitta brings about this conversion with Dhatwagnis. The nutrients absorbed are subjected to metabolism in the body. Metabolism of glucose occurs in muscles and other tissues, conversion of fat in adipose tissue, oxidation of glucose to give energy, synthesis of glycoproteins, and non-essential amino acids; all take place at this stage.

The very first tissue to be formed is plasma (Rasa Dhatu) and then other tissues are formed subsequently. Plasma is rich in digestive nutrients and further transfers these nutrients to subsequent tissues. In this way, all the complex tissues are formed and get nourishment.

Ayurveda is the greatest gift of sages that explains every stage and process of the body. It explains the importance of food that we intake and the action of Agni on it. It also signifies its relevance to modern physiology. With its basics, it gives truly pure information about the wear and tear of the body.