I think the most fascinating thing about this is the study that said it was happening to lab animals with controlled diets, also.
Pet hypothesis: It takes a large amount of energy to maintain our body temperature. What if one cause is the spread of climate control. AC and affordable indoor heat mean we don't spend much energy on thermal regulation.
I don't know, looking at this obesity map[1] I don't see much of a difference between northern/southern states. If anything there are more southern states with extreme (35%+) obesity. Doesn't mean it doesn't contribute partially though. It's also very crude data.
Here's a graph with the prevalence of AC by region. It could also be related to the affordability of heat (my grandparents kept the house very cool). I have no idea if there's something to this, but interesting to poke at.
I'm middle-aged, and even out in the sticks we had window air-conditioning. And affordable indoor heating has been a thing since long before I was born. Yet oddly enough, previous generations weren't butterballs. I didn't play a lot of Nintendo growing up, though.
An interesting hypothesis, but I think it easier to point to sedentary lifestyles and poor Western diets before I go off on a tangent like that.
Interesting. I never heat or cool my house (other than opening the windows), and while not being particularly careful with my diet, I've never had any weight issues. I think your hypothesis merits further investigation.
Pet hypothesis: It takes a large amount of energy to maintain our body temperature. What if one cause is the spread of climate control. AC and affordable indoor heat mean we don't spend much energy on thermal regulation.