What is a bad tasting food in the first place? It simply does not taste as good as unhealthy foods due to lower fat and sugar aka carbs. At least our brain thinks so. Almost every human is fuled by carbs. We need it to feel productive and energetic - high blood sugar level. The brain is used to this and tells us to eat sugary food so we wont feel bad - low blood sugar level.

Fat is very flavour enhancing so most stuff tastes way better with bad fats. There are also good fats. Most of the time they are mixed e.g. Olive oil - some bad fats and mainly good fats.

Combine these 2 and you get e.g. Potato chips. If you eat them they feel like nothing in your mouth, they feel like they desolve so your brain thinks "i hardly had any chips so i sure can eat more"

This is all i know. There might be more to it.