5 Not-So-Obvious Reasons We're Fat Looking beyond lack of willpower By Nick McMaster, Newser Staff Posted Mar 4, 2011 3:28 PM CST 14 comments Comments In this photo taken Thursday, Sept. 17, 2009, fifteen-year-old Amorette Castillo has her sensor checked before starting a series of physical activities at a lab in Alhambra, Calif. (AP Photo/Kim Johnson Flodin) (Newser) – The number of overweight Americans keeps, umm, ballooning, but why? LiveScience looks past self-control issues and too little exercise to some less-discussed factors. So many of us are fat because of: The government: 29 million Americans instantly became overweight in 1998 when the government lowered the overweight threshold from a body-mass index of 28 to 25. Better hygiene: As antibiotics and anti-bacterial soaps killed off "bad bacteria," they also eliminated the competition, possibly allowing intestinal bacteria that increase appetite and suck more calories from food to prosper. Our parents: You inherited a whole mess of body-weight factors from your parents, including how easy it is to be satiated. And research indicates that a woman's eating habits during pregnancy can also influence the expression of obesity-related genes. Our friends: If your friends are fat, you are likely to be so yourself, studies have suggested—mainly because your friends set what you consider normal. Fast food culture: Eating on-the-go can leave you perpetually unsatisfied. And fast food loaded with fats, sugar, and salts hit the "reward" areas of the brain, functioning a little like an addictive drug. Click for more reasons.