It sounds like strange dietary advice, but there's real chemistry behind it.
As cheese ages, proteins slowly break down into smaller molecules. One of them is tyramine, a naturally occurring compound named after the Greek word tyros, meaning ""cheese."" Tyramine is also found in fermented foods such as cured meats, soy products, and some wines.
For most people, this isn't a problem. An enzyme called monoamine oxidase (MAO) quickly breaks tyramine down before it reaches the bloodstream in significant amounts.
But things change if that enzyme is blocked.
Global Chemical Database