Taittiriyaka-Upanishad: Third Valli, Seventh Anuvaka
Let him never abuse food, that is the rule.
Breath is food, the body eats the food. The body rests on breath, breath rests on the body. This is the food resting on food. He who knows this food resting on food, rests exalted, becomes rich in food, and able to eat food (healthy), becomes great by offspring, cattle, and the splendour of his knowledge (of Brahman), great by fame.