moderation is its own medicine; take care of your stomach; don't overeat
Proverb warning against overeating and overdrinking; literally 'the belly is also part of one's body', implying that harming your stomach harms yourself.
As the saying goes, 'moderation is its own medicine,' so let's be careful not to overeat.
飲み会でつい飲みすぎてしまうけど、腹も身の内だよね。
I tend to drink too much at parties, but you know, take care of your stomach.
A traditional Japanese proverb; the exact origin is uncertain, but it reflects a common cultural emphasis on moderation in eating and drinking.