Why does asparagus make my urine smell?

It’s officially asparagus season. For those of us who love these vibrant green shoots this will be welcome news, but it may also serve as a significantly less welcome reminder of the rather pungent side effect of eating it – smelly wee.

But what exactly causes this seasonal sulfurous aroma and do we all produce it or are some of us lucky enough to leave the toilet bowl stink-free?