Yes. Food is really changed into the true human nature by reason of its assuming the specific form of flesh, bones and such like parts.
Alimentum vere convertitur in veritatem humanae naturae, inquantum vere accipit speciem carnis et ossis et huiusmodi partium.
This is what the Philosopher says (De Anima ii, 4): "Food nourishes inasmuch as it is potentially flesh."
Et hoc est quod dicit philosophus in II de anima, quod "alimentum nutrit inquantum est potentia caro."
According to the Philosopher (Metaph. ii), "The relation of a thing to truth is the same as its relation to being." Therefore that belongs to the true nature of any thing which enters into the constitution of that nature.
Secundum philosophum, II Metaphys., "hoc modo se habet unumquodque ad veritatem, sicut se habet ad esse." Illud ergo pertinet ad veritatem naturae alicuius, quod est de constitutione naturae ipsius.
But nature can be considered in two ways: firstly, in general according to the formal aspect of the species; secondly, as in this individual. And whereas the form and the common matter belong to a thing's true nature considered in general, individual signate matter, and the form individualized by that matter, belong to the true nature considered in this particular individual. Thus a soul and body belong to the true human nature in general, but to the true human nature of Peter and Martin belong this soul and this body.
Sed natura dupliciter considerari potest, uno modo, in communi, secundum rationem speciei; alio modo, secundum quod est in hoc individuo. Ad veritatem igitur naturae alicuius in communi consideratae, pertinet forma et materia eius in communi accepta, ad veritatem autem naturae in hoc particulari consideratae, pertinet materia individualis signata, et forma per huiusmodi materiam individuata. Sicut de veritate humanae naturae in communi, est anima humana et corpus, sed de veritate humanae naturae in Petro et Martino, est haec anima et hoc corpus.
Every virtue of a passible body is weakened by continuous action, because such agents are also patient. Therefore the transforming virtue is strong at first so as to be able to transform not only enough for the renewal of what is lost, but also for growth. Later on it can only transform enough for the renewal of what is lost, and then growth ceases. At last it cannot even do this; and then begins decline. In fine, when this virtue fails altogether, the animal dies. Thus the virtue of wine that transforms the water added to it, is weakened by further additions of water, so as to become at length watery, as the Philosopher says by way of example (De Gener. i, 5).
Omnis virtus in corpore passibili per continuam actionem debilitatur, quia huiusmodi agentia etiam patiuntur. Et ideo virtus conversiva in principio quidem tam fortis est, ut possit convertere non solum quod sufficit ad restaurationem deperditi, sed etiam ad augmentum. Postea vero non potest convertere nisi quantum sufficit ad restaurationem deperditi, et tunc cessat augmentum. Demum nec hoc potest, et tunc fit diminutio. Deinde, deficiente huiusmodi virtute totaliter, animal moritur. Sicut virtus vini convertentis aquam admixtam, paulatim per admixtionem aquae debilitatur, ut tandem totum fiat aquosum, ut philosophus exemplificat in I de Generat.