Why do women (or anyone for that matter) become fat?
For the same reason anyone else becomes fat, because they eat too much.
The only way to fix it is to either eat less, or do things that burn more energy (exercise, get physically demanding jobs, use stairs more often, etc.).
Plus some people seem to believe in the concept of comfort food, which contributes to weight gain.
There are others, though thankfully a very, very small minority, that get erotic feelings from eating and becoming fatter. At least it's so small that I've never met a woman like this.
Some people are like me; they eat just enough to not feel hungry anymore, and then stop. I've been the same size for five (almost six) years now, always weighing the same. My weight hasn't deviated by more than a pound or two in either direction. I suppose the fact that I shy away from foods that really make you fat helps. I can't remember the last time I ate a candy bar or some ice cream. I sometimes eat cookies, but rarely. I might get some chocolate candy from the vending machine if I'm really hungry and there's nothing better available. As for chips, I always buy those organic corn chips with salsa, though even that is uncommon.
I think that most people would not gain a significant amount of weight if they do what I do. I'm not afraid to leave food on the table if I'm full or not feeling hungry anymore. Besides, I can always save it for later.
I never eat, and in fact hate "diet," "low fat," "no sugar," or "light" foods. Yet I haven't gained any weight in the last five years. So why is that?
So basically, eat whatever you like, but don't go overboard, and you won't get fat.
Here's another idea: If you eat meat, like most people, buy the leanest meat the store has (it'll cost more, but it's more meat and less fat, and thus a good buy), and trim the fat that's left.
Also, don't buy into that fad diet crap. They rarely, if ever work. The Atkin's diet is a good example. My mother has a coworker who's been on the Atkin's diet for years, but hasn't lost any weight. I eat what could be considered a reverse Atkin's diet, but I'm not fat.
Just my $.02,
Ben
Also notice that the three least obese countries in the survey are Non-Western European countries. 
