meal-breaker

A foodstuff (usually a sweet, salty, oily or fatty snack) which unexpectedly spoils one's appetite. After consumption, the eater usually cannot start or finish the remainder of their regular meal.

I thought I'd just have a bag of buttered popcorn to take the edge off before dinner, but that's stuff's a real meal-breaker!

Meal breaker

An unwanted ingredient in a dish that makes the entire thing inedible.

I can't order that, it's got coriander. You know that's a meal breaker for me.

Does this have any type of nut in it? Because that's an instant meal breaker.