Shatapatha Brahmana 10.1.4.12

10.1.4.12

prāṇena vai devā annamadanti agniru devānām prāṇastasmātprāgdevebhyo juhvati prāṇena hi devā annamadantyapānena manuṣyā annamadanti tasmātpratyaṅmanuṣyeṣvannaṃ dhīyate'pānena hi manuṣyā annamadanti

By means of (the channel of) the out- (and in-) breathing the gods eat food, and Agni (the sacrificial fire) is the out-breathing of the gods; whence it is in front (of the sacrificial ground) that offering is made to the gods, for by means of the (channel of the) out-breathing the gods eat food. By means of the down-breathing men eat food, whence food is introduced into men (from the front) towards the back, for by their down-breathing men eat food.