Food has a three-fold form as coarse, middle and subtle
portions. The Chandogya Upanishad says that the element
Tejas, when it is related to food, takes the form of oil, butter etc. The gross portion becomes bone; the middle portion becomes the marrow and the subtle portion becomes speech. The mind is supported by anna (food); prana (vital airs) is held up with water; speech is aided by Tejas. Uddalaka explains all this to his son Svetaketu, said M.K. Srinivasan in a discourse.
Uddalaka further says that when we eat food, the mind is
pleased. When water is consumed, prana is pleased. When
Tejas is absorbed, speech is supported.This does not mean that mind, prana and speech are the products of anna (food), Ap (water) and Tejas. Food is something that is pleasing to the mind — Aapyaayana.
To teach Svetaketu the importance of food, Uddalaka
tells him to abstain from food for 15 days. At the end of the
period, he asks Svetaketu to recite the Vedas, but Svetaketu says that he is unable to recall anything. Uddalaka explains why it is so. The mind has 16 divisions, and because of fasting, 15 of them have been lost. He then asks Svetaketu to have some food.
After Svetaketu has eaten, Uddalaka asks him to recite
the Vedas and Svetaketu is able to recollect them.
Uddalaka says that the one division of the mind that had
remained has been rekindled by the food that Svetaketu
has eaten, and that has made possible his recollection of
the Vedas. Thus the mind is supported by food, the sage
In the seventh chapter of this Upanishad, it is pointed
out that pure food keeps the mind pure, thus showing the
food-mind connection clearly.