Here's 10 from NPR
with my comments in italics:
Day to Day, July 10, 2006 · New research suggests that lack of sleep and environmental toxins are just as likely to cause obesity as eating fast food or failing to exercise. Dr. Sydney Spiesel, a Yale Medical School professor and a contributor to Slate, talks with Madeleine Brand about new research that lists other possible causes of obesity.
1. Inadequate sleep -- average amounts of sleep have fallen among Americans, and many studies tie sleep deprivation to weight gain.
I've heard about various studies on this one, including that lack of sleep causes carb cravings. Of course, it runs counter to the idea that fatness is a matter of low-status self-indulgence (junk food and tv), but then, so do the rest of these.
2. Increased consumption of endocrine disruptors, substances in some foods that may alter fats in the body.
I have no details on this one. I wonder if it's hormones in meat.
3. Climate-controlled environments. Air conditioning and heating limit calories burned from sweating and shivering.
Does sweating burn more calories than being in a cool environment? On the other hand, people may eat less when they aren't cooled.
4. Decrease in tobacco use. Smoking is often linked to appetite suppression.
5. New prescription medicines that promote weight gain.
This is a big one.
6. Changing demographics -- there are now more middle-aged and Hispanic Americans, groups that have higher obesity rates.
7. Women giving birth at an older age, which correlates with heavier children.
8. Genetic influences during pregnancy -- a so-called "fetally-driven positive feedback loop."
9. Natural selection -- heavier people tend to survive tough times better than skinnier humans.
Presumably just a claim that some people are naturally fatter than others.
10. Assortative mating, or "like mating with like" -- meaning fat people procreating with others of the same body type, gradually skewing the population toward the heavy end.
I think this translates as fewer medium-sized people. I don't know whether there's any evidence of that happening.
Source: International Journal of Obesity
And two more from me:
11. Dieting--there are a lot of anecdotes about people gaining back an extra 25 pounds or so every time they lose significant weight, and maintaining a stable weight when they stop dieting. While afaik there isn't evidence that dieting slows metabolism, there is evidence that it increases the background level of hunger. In any case, it ien't rare for people to do serious dieting three or four times--and if they're in this pattern, it's enough to move them from somewhat fat to definitely fat.
12. Stress--I've read somewhat that stress makes it hard to lose weight. This seems reasonable--a fight or flight reaction is precisely about being ready to handle emergencies fast and putting off maintenance until life gets calmer. Taking calories out of fat storage might be one of those slow things compared to just finding some carbs and eating them. Fat people are apt to be stressed by the prejudice against them.