Taittiriya Upanishad 3.7.1

3.7.1

annaṃ na nindyāt /
tadavratam /
prāṇo vā annam /
śarīramannādam /
prāṇe śarīraṃ pratiṣṭhitam /
śarīre prāṇaḥ pratiṣṭhitaḥ /
tadetadannmanne pratiṣṭhitam /
sa ya etadannamanne pratiṣṭhitaṃ veda pratitiṣṭhati /
annavānannādo bhavati /
mahānbhavati prajayā
paśubhirbrahmavarcasena /
mahān kīrtyā // 1//
iti saptamo 'nuvākaḥ //

His vow is that, he should not deprecate food. The vital force is verily the food, and the body is the eater; for the vital force is lodged in the body. (Again, the body is the food and the vital force is the eater, for) the body is fixed on the vital force. Thus (the body and vital force are both foods; and) one food is lodged in another. He who knows thus that one food is lodged in another, gets firmly established. He becomes a possessor and an eater of food. He becomes great in progeny, cattle, and the lustre of holiness and great in glory.