Shatapatha Brahmana 10.4.1.18

10.4.1.18

tasmā etasmai prāṇāya etāḥ ṣoḍaśa kalā annamabhiharanti tā yadānabhihartuṃ dhriyante'thaitā eva jagdhvotkrāmati tasmādu haitadaśiśiṣatastṛpramiva bhavati prāṇairadyamānasya tasmādu haitadupatāpī kṛśa-iva bhavati prāṇairhi jagdho bhavati

These sixteen digits convey the food to that vital air; and when they take to conveying no food to it, then it consumes them and departs (from the body): hence he who is hungry here, feels very restless, consumed as he is by his vital airs; and hence he who suffers from fever becomes very thin, for he is consumed by his vital airs.