How It Grows

One Fifty-seven discusses the eighth element, 'nutritive essence'.  It is produced by karma, consciousness, temperature, and nutriment itself.  One can look at any rupa-kalapa and see how it multiplies forth again and again.

From a commentary on the Abhidharma: 

. The “Atthasalini” (II, Book II, Ch III, 330) explains that there is foodstuff, the substance which is swallowed (kabalinkaro aharo, literally, morsel-made food), and the “nutritive essence” (oja). The foodstuff which is swallowed fills the stomach so that one does not grow hungry. The nutritive essence which is in food preserves beings, keeps them alive. The nutritive essence in gross foodstuff is weak, and in subtle foodstuff it is strong. After eating coarse grain one becomes hungry after a brief interval. But when one has taken ghee (butter) one does not want to eat for a long time (Atthasalini, 331). The “Atthasalini” (332) gives the following definition of nutriment (See also Visuddhimagga XIV, 70.):

As to its characteristic, etc., solid food has the characteristic of nutritive essence, the function of fetching matter (to the eater), of sustaining matter as its manifestation, of substance to be swallowed as proximate cause.