>Fifty years ago, two-thirds of the USA were not obese. Biology has not changed in that time. What has? Other commentators have mentioned the food aspect, but

>Fifty years ago, two-thirds of the USA were not obese. Biology has not changed in that time. What has? Other commentators have mentioned the food aspect, but there are significant lifestyle changes since the 50s. The rise of the suburbs greatly reduced the amount of walking for many Americans to basically just walking to a car in the morning and walking from a car in the evening, with maybe some walking back and forth to a bathroom or water cooler in between. Contrast that to the past where most American cities were laid out with public transit in mind (including LA; it used to boast a larger rail system than NYC). This meant burning more calories just to exist. I myself moved from the land of sprawl to a walkable urban city and I lost quite a bit of weight since most, but not all, of my trips were on foot, bike, or public transit. Very few trips were undertaken in a car. I then moved to NYC and get even more activity, though that's counterbalanced by the delicious food everywhere. You'll notice that most walkable urban areas tend to be slimmer than sprawling areas, all else being equal.