I know you will laugh at this question but....?

my boyfriend has been farting alot lately!and i mean loads...and it smells really really bad?it's to the point i's annoying him as he's never farted this bad before?it's non stop aswell.could this be to do with his diet?he dosn't really eat healthy but alot better than he used to and yet it's worse?i don't get it how it's just changed and gone bad?can anyone tell me?