There is an advice, narrated from Ibn Abi ad-Dunya who narrated from Muhammad bin Wasi that he said, “Anyone who eats little food will easily understand (learn), make others easy to understand, cleaning, and be kind. Verily, eating a lot will prevent ones from achieving their goal.”
There is another narration from Utsman bin Zaidah, he said that Sufyan ats-Tsauri sent a letter to him (which among the contents), “If you want your body to be healthy and able to sleep less; eat less.”
One advice which narrated by Ibrahim bin Adham: “Anyone who takes care of his stomach, naturally he will safeguard his religion. Anyone who can control his hunger, he will master the good manners. Verily, hunger will hinder ones from disobedience, whereas a full stomach will bring it close, and it will come to him a sense of pleasure and arrogance.”
Also narrated by asy-Shafi’i: “… A full stomach will burden the body, removing vigilance, causing drowsiness, and preventing its owner from worshipping Allah.”
Allah knows Best!
Source: Jami ‘al-Ulum wal Hikam, pages. 576 – 577