In De anima ii 4.416b28-29, Aristotle says: 'All food must be capable of being digested, and that whose activity causes digestion is heat.
ɪn də ˈænɪmɚ ɹˌoʊmən tˈuː fˈoːɹ.fˈoːɹhˈʌndɹɪd sˈɪkstiːn bˈiː twˈɛnti ˈeɪt dˈæʃ twˈɛnti nˈaɪn, ˈæɹɪstˌɑːɾəl sˈɛz: ˈɔːl fˈuːd mˈʌst biː kˈeɪpəbəl ʌv bˌiːɪŋ daɪdʒˈɛstᵻd, ænd ðæt hˌuːz æktˈɪvᵻɾi kˈɔːzᵻz daɪdʒˈɛstʃən ɪz hˈiːt.