Mind is made up of food. Breath (vital force) is made up of water. Speech is made up of heat. (so ends Chandogya Upanishad, 6.6)
Chandogya Upanishad 6.7
As an experiment, in a bid to further a deeper understanding, śvetaketu was asked, by his father, not to eat for fifteen days but to drink as much water as he needed. Since the vital force is made up of water life will be maintained.
When fifteen days were up, śvetaketu returned to his father and asked what he should recite.
His father said, "Mantras from ṛg Veda, Yajur, and Sāma."
śvetaketu, no matter how hard he tried, could not bring any mantras to mind.
His father then said, "Listen to this example. When a huge fire, with a lot of fuel, has reduced to an ember the size of a firefly, with very little fuel, that fire can no longer burn very much. Similarly you are left depleted, for want of food, and can not bring the veda to mind. Eat now and then you will understand everything."
śvetaketu took food and, as promised, he was able to reply to each and every question his father asked.
His father said, "When a huge fire, with a lot of fuel, has reduced to an ember the size of a firefly, if one then adds dry straw to that tiny ember, it would once again flare up and burn very strongly.
In similar fashion, my son, you were left depleted for want of food and when nourished by food, mind once again blazed up and you remembered, and could speak of, the Vedas.
Mind is made up of food. Breath (vital force) is made up of water. Speech is made up of heat." (so ends Chandogya Upanishad, 6.7)