Literally: it doesn’t eat the bread

Meaning: It doesn’t cost much; it won’t do any harm; it’s not a big deal

Origins: Middle Ages when the bread was an essential base of the food. Bread was an important part of the families’ food budget.

The expression was then used in the 17th century, which was a time of famine and death in France. The expression survived over the centuries, still in use today.

it is a colloquial expression that is usually delivered with a shrug, and when spoken, the ne and the de are often swallowed, so that you will hear it as, “Ça mange pas d’pain.”

Example:

« Ici, ils ont l'impression de reconstruire un monde, ça ne mange pas de pain. » Daniel Pennac - Au bonheur des ogres