>>13310415Foods high in fat and sugar are better energy sources. So your body tells you to eat those chunks of meat instead of a mostly water salad.
Also in nature sweet foods are usually also high in vitamins, which makes them desirable for a healthy diet. Simple sugars also give quick energy boosts which makes them useful for an active hunter or gatherer lifestyle.
Obviously artificially created sweets that are basically just crystal sugar and syrup do not fit that description and are incredibly unhealthy. And you desire those because they are even more sweet than fruits. If you then also sit on your ass all day, then all of that quick energy released by the simple sugar gets stored as body fat instead.
I wouldn't say fatty foods are necessarily unhealthy. That's an outdated idea from 30 years ago. It's more simple sugars that fuck up your health and make you fat.
That said, heavily processed fats like trans fats are unhealthy. Same goes for an imbalance of omega 6 and 3 oils. Also some forms of meat roasting can create carcinogenics which can cause cancer. Don't buy crappy fast food.