Eating - and its etiquette briefly explained by Imam Sadiq (as).

A little food is praiseworthy in every case and with all people, because it
is salutary for the outer and the inner being. Eating is praiseworthy
when done out of necessity, as a means and provision, at a time of
plenty, or for nourishment. Eating out of necessity is for the pure; eating
as a means and provision is a support for the precocious; eating at a
time of plenty is for those who trust; and eating for nourishment is for
believers.

There is nothing more harmful to the believer's heart than having too
much food, for it brings about two things; hardness of heart and arousal
of desires. Hunger is a condiment for believers, nourishment for the spirit,
food for the heart, and health for the body. The Holy Prophet said,

'The son of Adam fills no worse vessel than his belly.'

David said, 'Leaving a morsel of food that I need is preferable to me
than staying up for twenty nights.'

The Messenger of Allah said, 'The believer eats to fill one stomach, and

the hypocrite seven.' And elsewhere, 'Woe to people who are swollen in

two places!' When he was asked what they were, he replied, 'The stomach

and the genitals.'

‘Isa [a] said, 'The heart does not have any worse disease than hardness,

and no soul has been more weakened than by lack of hunger. They are

two halters of banishment and disappointment.'

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Reference: Imam Sadiq (as)'s ahadith on Eating in the book Lantern of path, chapter on Eating.