Bhagavad Gita Verse 14, Chapter 15

aham vaishvaanaro bhootvaa praaninaam dehamaashritaha |
praanaapaanasamaayuktaha pachaamyannam chaturvidham || 14 ||
 
Residing in the bodies of all beings, I become Vaishvaanara. In conjunction with Praana and Apaana, I digest the four types of food.
 
aham : I
vaishvaanaraha : Vaishvaanara
bhootvaa : become
praaninaam : of all beings
deham : bodies
aashritaha : residing
praanaapaana : Praana and Apaana
samaayuktaha : in conjunction with
pachaami : digest
annam : food
chaturvidham : four types
 
Previously, we saw how Ishvara sustained and nourished all beings on this earth by providing them with nutrition in the form of plant life and vegetation. The energy stored in this food has to be absorbed and assimilated into all living beings. How does that happen? Shri Krishna says that Ishvara manifests himself as Vaishvaanara, the fire inside all living beings which represents the process of metabolism.
 
It is a wonder that we are able to eat such a large variety of food, and yet derive enough energy to keep our bodies running throughout our lives, all due to the functioning of the Vaishvaanara fire. It is supported by two vayus or forces known as the Praana and the Apaana vayus. The Praana vayu brings food towards the digestive organs. Vaishvaanara is the process of digestion and metabolism. The Apaana vayu pushes non-essential portions of the food out into the world.
 
We also come across the four types of food that are referenced in scriptures. These are : food that can be chewed such as rice, food that can be sucked such as mango nectar, food that can be drunk such as fruit juices, and food that can be licked such as pickles. The Vaishvaanara fire can convert all these types of food into energy for the body.
 
So we see that production, distribution and ultimate consumption of energy that happens in us, and happens in any other living being, is nothing but Ishvara. Ishvara is the producer, distributor and consumer. Remembering this topic is a great way to reduce our ego and see our oneness with the world. Many people in India, in fact, chant the 15th chapter before their meals in order to pray for good digestion.