Well, it depends on the woman and what she wants or doesn't want. Unless they intentionally want to gain it often seems to take getting knocked up, and/or finding some abusive asshole (in childhood or adulthood) who abuses and demeans them until they start eating their feelings of inadequacy. Sometimes it's an office job. Sometimes it's a drinking problem (see above). Sometimes it's an illness or hormonal imbalance (Google PCOS) Not all women get fat.
5 years
She was skinny as a kid up until puberty, when her boobs grew. She's short, but was one of those girls with boobs out of proportion with the rest of her. She had her first child at 18, when the weight piled on easily, from what she says; literally gained about a hundred pounds, plus she wasn't working for a long time. By the time we met a few years ago, she'd been north of 300 pounds for about 15 years. She's sexy and confident about it, though, which is all that matters