Why?
Have you stopped to think about this? Why are we facing an obesity epidemic?
Here's my view: Its the dissociation of physical stimuli from their naturalistic purposes.
I'm calling it 'Naturalistic Dissociative Disorder' or NDD. Lets consider it in a comparative sense relative to sexuality, which is also exhibiting similar effects.
So, why does food taste good/bad/at all? To get you to eat, and more specifically, to get you to eat certain things and not others. You need to eat, because you require nutritional value to live as an organism. Hence, things have a taste, that you might be able to discern that which is desirable for consumption and that which is not, and so that you'll be motivated to consume such that you can survive.
But what happens when that physical stimuli gets dissociated from the Darwinian motivation? This isn't some deity that made it this way, but evolutionary processes over millions of years - you get taste stimuli to avoid eating shit, while being motivated to eat nutritionally-valuable materials… So, what happens when, via one mechanism or another, you can dissociate the "tastes good" and the "offers nutritional value"? You get problems, quickly. See, I can make a piece of cardboard that tastes delicious - negative nutritional value, but, highly tasty. When NDD comes into play in this context, you'll no doubt have people willing to eat cardboard if it tastes juuuuust right. And that's why we have obesity today - people don't eat because they need to power their bodies, they don't even think of it that way. They eat because it feels good, it taste good, they enjoy it… The nutritional value? Tertiary concern, at best.
Same goes for sexuality. Wanna know why our culture is degenerating rapidly in the context of sexuality? NDD again. Prophylactics, birth control and abortion have all contributed to the societal contextual acceptance of the complete dissociation of sex and reproduction.
Why does sex feel good? So you'll do it, and reproduce. That's literally all there is to sexual stimuli - it feels good, so you'll do it, so you'll make more of yourself.
But what happens when, through one mechanism or another, you are able to dissociate the pleasurable sexual stimuli from the act of reproduction? You get all sorts of rampant and grotesque sexual 'exploration', a groping in the dark in constant pursuit of cummies, while doing everything in your power to avoid the act of reproduction, which is, once again, the sole evolutionary motivation for sex being pleasurable.
This dissociation of physical stimuli from the naturalistic evolutionarily-derived purpose is terribly destructive, driving people into constant pursuit of those stimuli, and constant avoidance of (or simply absence of care for) the phenomenon which caused this state to emerge to begin with.
Why does sex feel good? So you'll do it and reproduce.
What if you derive a mechanism to avoid the reproduction? People will pursue the pleasure instead.
Why does food taste good? So you'll eat it and gain the nutritional value.
What if you derive a mechanism to avoid the nutriotional value? People will pursue the pleasure instead.
This is how species die, and I become more convinced each day that this NDD effect is the Great Filter - and we've already failed the test.