The Holy Prophet (S) said: "There are three traits which Allah loves (in people): briefness in speech, short (length) of sleep, and small (portion) of food; while there are three traits which He dislikes (in them): loquaciousness, oversleeping, and overeating."
Al Ithna'Ashariyyah, p. 92
The Holy Prophet (S) said: "Try to be clean as much as you are able to. Verily, Allah has based the foundation of Islam on cleanliness; hence, never can a person enter Paradise but the clean ones."
Kanz-ul-'Ummal, Tradition 26002
Imam Amir ul Mu'mineen ‘Ali (‘a) said: "Overindulgence of food causes various kinds of diseases."
Ghurar-ul-Hikam, p. 359
Imam Musa ibn Ja'far, the seventh Imam, (‘a) said:
"There are five sunnah about the head and five others related to the body. The first five concerning the head, are: washing the mouth, trimming the moustache, combing the hair, and drawing up water through the mouth and nostrils.
The second five, concerning the body, are: circumcision, shaving the pubic hair, depilating the armpits, clipping the nails, and cleansing the privy parts (with water, tissue, cloth, etc., while water is preferable)."
Khisal by Saduq, p. 125
Imam Amir ul Mu'mineen ‘Ali (‘a) told Imam Hasan (‘a): "Shall I teach you four traits by which you will be in no need of any medical treatment?"
"Yes," Imam Hasan answered. Then, ‘Ali (‘a) said:
Do not sit for food (in order to eat) unless you are hungry;
And, do not leave the (table of) food but you still have an appetite for it;
Chew (your food in your mouth) well;
And, when you want to go to bed, (primarily) go to the water-closet to ease nature.
If you take these in action, you will be in no need of any medical treatment."
Wasa'il-ush Shi'ah, vol. 24, p. 245