Probably more or less the same as to what happens with skinny people who have a garbage diet but just eat less or have significantly higher metabolisms.

It's not great.

The good news is it's quite commonly reported (and I can add my anecdotal experience to the chorus) that I don't crave the food that's worst for me in any real quantity anymore. Even if I'm busy and need to scroll through uber eats, I'm not using it as an excuse to get a delicious but large, fried, high in carbs, high in fat meal. It's way easier for me to say "yeah that tastes good, but I'll grab the grilled chicken wrap and brown rice."

I'm not sure on what causes this - we have some preliminary studies around GLP1 peptides, dopamine, addiction, etc., so it might be something there. But the sheer number of people you hear talking about it makes me believe we'll have some studies that do look into it in the future. It might not happen to everyone, and some people might still just choose to eat poorly even if it does, but in both situations people's longterm health depends on them listening to advice on how to eat better and exercise, and I think most people would rather be average weight and metabolically unhealthy than obese and metabolically unhealthy.