Yoga talks about pranas and vayus. Just the way we have motor and reflex nerves in our body-brain system, these pranas are motor and reflex impulses. There are basically five pranas - Prana, Apana, Samana, Vyana and Udana. Today we will talk about the first three. In reality, prana is one but each function it performs is given a name.
Yoga says Prana, Apana and Samana are responsible for the digestion of food. When food is swallowed, science says digestive juices act upon it. Yoga says it is the prana called Samana which brings about digestion of the food we eat. Once the food is digested, Prana transmits nourishment to every cell of the body, just the way blood is circulated. Once the food is broken down in the cells, waste matter is produced and that is eliminated from the body by the prana called Apana.
My teacher Tavariaji always insisted that students of yoga eat one meal a day. The science behind his saying so was the working of these pranas. Each prana has an 8-hour cycle. Samana is dominant from noon, when the sun is at mid-heaven, to 8pm. This is when we should eat our food. From 8pm onwards, once the food is digested, Prana carries the nourishment to every cell of the body. This lasts till four in the morning at which time, the cycle of Apana takes over which expels waste matter from the body till 12 noon.
Each of these cycles should work independently; otherwise, disease enters the body. So, if Apana is active in the morning to eliminate waste, we should not be loading up on breakfast, and the same goes for a heavy dinner too.
Tavariaji would say that food remains in the stomach for three to four hours and the action of Samana goes on for 4 hours after eating. Deducting 4 hours from 8pm, he would say we should eat one meal between noon and 4pm to remain healthy.
Modern dieticians say you can have very light meals during the other periods also, but I am sure my teacher would never agree to this.