Chandogya Upanishad 7.9.1

7.9.1

annaṃ vāva balād bhūyaḥ \
tasmād yady api daśa rātrīr nāśnīyāt \
yady u ha jīvet \
athavādraṣṭāśrotāmantāboddhākartāvijñātā bhavati \
athānnasyāye draṣṭā bhavati śrotā bhavati mantā bhavati boddhā bhavati kartā bhavati vijñātā bhavati \
annam upāssveti \\709.1\

1. ‘Food (anna), assuredly, is more than Strength. Therefore, if one should not eat for ten days, even though he might

live, yet verily he becomes a non-seer, a non-hearer, a non-thinker, a non-perceiver, a non-doer, a non-understander. But on the entrance of food he becomes a seer, he becomes a hearer, he becomes a thinker, he becomes a perceiver, he becomes a doer, he becomes an understander. Reverence Food.