Thy can, when it comes to their body weight lol

Eat

For all intensive purposes its the same.

It literally isn't. Literally, "on" doesn't translate to "en", as it literally means "in". Literally, the "masse" in French here doesn't refer to literal "mass" as in a quantity of literal matter to be literally measured, but literally an uncountable concept like a literal crowd, for example.

So, which mass are you quitting on?

And in any case, to be literally correct the expression taken from another literal language should be literally italicized.

https://dictionary.cambridge.org/dictionary/english/en-masse