Related to: Babies and Bunnies: A Caution About Evo-Psych, Superstimuli and the Collapse of Western Civilization.
The main proximate cause of increase in human weight over the last few decades is over-eating - other factors like decreased energy need due to less active lifestyle seem at best secondary if relevant at all. The big question is what misregulates homeostatic system controlling food intake towards higher calorie consumption?
The most common accepted answer is some sort of superstimulus theory - modern food is so tasty people find it irresistible. This seems backwards to me in its basic assumption - almost any "traditional" food seems to taste better than almost any "modern" food.
It is as easy to construct the opposite theory of tastiness set point - tastiness is some estimate of nutritional value of food - more nutritious food should taste better than less nutritious food. So according to the theory - if you eat very tasty food, your appetite thinks it's highly nutritious, and demands less of it; and if you eat bland tasteless food - your appetite underestimates its nutritious content and demands too much of it.
It's not even obvious that your appetite is "wrong" - if you need certain amount of nutritionally balanced food, and all you can gets is nutritionally balanced food with a lot of added sugar - the best thing is eating more and getting all the micro-nutrients needed in spite of excess calories. Maybe it is not confused at all, just doing its best in a bad situation, and prioritizes evolutionarily common threat of too little micronutrients over evolutionarily less common threat of excess calories.
As some extra evidence - it's a fact that poor people with narrower choice of food are more obese than rich people with wider choice of food. If everyone buys the tastier food they can afford, superstimulus theory says rich should be more obese, setpoint theory says poor should be more obese.
Is there any way in which setpoint theory is more wrong than superstimulus theory?
As has been pointed out, modern "traditional" foods are of a quality that was available only to the very rich, if even them. Moreover, that perception is easily biased by social norms; it's fairly likely you have been predisposed to dislike foods more associated with low social class and poor health.
Also, "nutritious" does not mean what you think it means. People have a taste for nutrient rich foods, not nutrient dense foods, and the main nutrient scarcity in the ancestral environment was likely (if not almost invariably) macro-nutritional, i.e. people didn't get enough calories, rather than people didn't get enough vitamins (people might also have not gotten enough vitamins, but this is somewhat less urgent). If you're eating whatever natural food you can find, and you're getting a fair amount of calories, you're not terribly likely to be severely malnourished.
The result of this is that taste now directs people to nutrient rich foods, like red meat and refined grains, and they consume them in volumes that exceed what the body can properly process. Nutrient dense foods (like spinach), on the other hand, don't taste very good, because our ancestors were so busy trying to get enough to eat that if they found nutrient-dense foods tasty, they'd starve to death.
I'd throw out an exception to the micronutrient point: sodium. We're suckers for sodium. I'm not aware of any other micronutrients that we can really taste directly.
Sodium also provides a fairly potent example that superstimulus theory makes more sense than setpoint theory. Salty foods are tasty because they are salty, not because the lack in other nutrients.
The same appears to be true for sugar. Adding sugar to foods generally makes them taste better (even foods that we don't think of as sweet, like french fries and tomato sauce); if setpoint theory was true, we would expect those foods to taste no different as long as haven't significantly altered the nutrient density.