In the name of Allah, Most Gracious, Most Merciful.
Miqdad bin Ma’dikarib (May Allah be pleased with him) reported: I heard Messenger of Allah (SAWS) say: “No man fills a container worse than his stomach. A few morsels that keep his back upright are sufficient for him. If he has to, then he should keep one-third for food, one-third for drink and one-third for his breathing.” (At-Tirmidhi).
Commentary: This Hadith dissuades us from overeating as this affects one’s health. Most illnesses come from overeating. When there is too much demand put on the stomach, we no longer digest correctly the foods that are crammed in beyond capacity. When the stomach is malfunctioning, it doubles the work of the liver and pancreas. This therefore leads to hepatism and everything that follows as constipation, hemorrhoids, intestinal spasms, gallstones etc … This can also cause diabetes due to deficiency of the pancreas. This finally causes obesity which is the main cause of arteriosclerosis and heart diseases. So by stating this basic principle of food hygiene, the Prophet (SAWS) has already stated in a few words half of medicinal science. The people who eat less are the people who live longer and are sick less often.
SAWS: May Allah exalt his mention and protect him from imperfection
Riyaadiss-Saliheen (The Meadows of the Righteous)
By Imam An Nawawi
Chapter 56, Page 169, No 516