Taittiriyaka-Upanishad: Third Valli, Ninth Anuvaka

Let him acquire much food, that is the rule. Earth is food, the ether eats the food. The ether rests on the earth, the earth rests on the ether. 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.