All praise is due to Allaah and may the prayers and salutations be upon His Messenger, to proceed:
Allaah the Most High said, "...And eat and drink and be not excessive (therein)..." (al-A'raaf 7:31)
Ibn Katheer commented upon this verse:
One of the Salaf said: Allaah has combined the entirety of medicine (at-tibb) in half a verse, "And eat and drink and be not excessive..."
Al-Qurtubi commented upon this verse, after mentioning that excessive eating is makrooh (disliked), he mentions the benefits of eating little:
... In eating little there are many benefits. From them that a man becomes of sounder body, of better memory, purer in understanding, (requiring) less sleep, and lighter in (his) soul...
Then he mentioned the harms of eating excessively:
... and in eating much there is the overstuffing of the stomach and putrefaction of undigested food, and from this the variety of diseases are produced, and thus he requires treatment more than what the one who eats little requires. Some of the physicians said, "The greatest treatment (dawaa') is (appropriate) estimation of (one's) food (intake)." And the Prophet (sallallaahu alayhi wasallam) has explained this meaning sufficiently and completely which does away with the speech of the physicians, so he said, "The son of Aadam does not fill a container worse than his stomach. It is sufficient for the son of Aadam to take enough morsels of food to keep his back straight (keep him able-bodied). And if it is necessary, then a third for his food, a third for his drink, and a third for his breath."...
Then a little later al-Qurtubi says:
And it is mentioned that (the caliph) ar-Rasheed used to have a shrewd Christian physician who said to Alee bin Hasan, "There is not in your Book (the Qur'aan) anything of the knowledge of medicine, and knowledge of is of two types, knowledge of the religions and knowledge of the bodies." So he said to him, "Allaah has combined all of medicine in half a verse in our Book." So he said, "What is it?" He said, "The saying of Allaah, the Mighty and Majestic: And eat and drink and be not excessive."...
And Imaam ad-Dhahabi in his book "at-Tibb an-Nabawi" (p. 34-35) says:
The Prophet (sallallaahu alayhi wasallam) said: "The son of Aadam does not fill a container worse than his stomach. It is sufficient for the son of Aadam to take enough morsels of food to keep his back straight (keep him able-bodied). And if it is necessary, then a third for his food, a third for his drink, and a third for his breath." This was reported by an-Nasaa'ee and at-Tirmidhee, who said, "Hasan Saheeh" ... and this is one from the aspects of preserving health.
Alee bin Hasan said: "And Allah, the Sublime and Exalted has combined the whole of medicine in (just) half a verse, so He, the Most High said, "And eat and drink and be not excessive..."
He is Alee bin al-Hasan bin Shaqeeq bin Muhammad bin Deenar bin Mush'ab, Abu Abdur-Rahman al-'Eedee al-Marwazi (d. 215H), the Imaam, the Haafidh, the Shaykh of Khurasaan, he came to Baghdad and narrated from the likes of Ibrahim bin Tahman, Abdullaah Ibn al-Mubaarak, Sufyaan bin Uyainah and others, and Ahmad bin Hanbal, Yahya bin Ma'een and others narrated from him, and his ahaadeeth are in the Six Books. He was a haafidh of a great amount of knowledge, and a haafidh of many books, including the Tawraat and Injeel and he debated the Jews and Christians. His biography can be found in all the major books of Rijaal.