It’s the nature of the addictive food you’ve been conditioned to love your whole life. They make you feel full(your body saying you got enough nutrition) when you didn’t get very much nutrition. So the full feeling stays while you get worse nutrition.
It’s also a modernized idea that we should eat until we are very full. Which is often not recommended. To me it seems more like your brain being conditioned against what is essentially “normal”, so you now feel like things are off.
chips and a kebab isn’t that much unhealthier than roast chicken and veges, theyre essentially the same thing, meat and veg. The main difference between these meals is one is much higher in fat. Fat lasts much longer in the stomach and thus allows you to fast much longer