The International Journal of Obesity says we’re facing a weight gain epidemic, and although one might assume that over-eating might have something to do with this problem, apparently that is incorrect. Here are the reasons we’re getting fat.

  1. Inadequate sleep. Average sleep amounts have fallen and many studies tie sleep deprivation to weight gain.
  2. Endocrine disruptors, which are substances in some foods that may alter fats in the body.
  3. Nice temperatures. Air conditioning and heating do limit calories burned from sweating and shivering.
  4. Fewer people smoking. Less appetite suppression.
  5. Medicines that cause weight gain.
  6. Population changes. More middle-ages and Hispanics, who have higher obesity rates.
  7. Older birth moms. That correlates with heavier children.
  8. Genetic influences during pregnancy.
  9. Darwinian natural selection. Fat people out-survive skinny ones.
  10. Assortative mating, or "like mating with like," as Allison puts it. Translation: fat people procreating with others of the same body type, gradually skewing the population toward the heavy end.