I don't think that discussing the huge range of reasons for a person being overweight is all that relevant - it's like trying to distinguish between the deservin and undeserving benefits recipients.
the main point is that women's bodies as shown in the mdeia are hugely unrealistic. Many many ways to tell if a person is a 'healthy weight' are deeply inaccurate (did you know that Tome Cruise has a BMI that ranks him as obese?). Just because we can see how big someone is doesn't give us a right to judge them and think we have a right to know their personal reasons for how they appear.
Why I am overweight is my own business, and I sometimes discuss it with my doctor. It has nothing to do with anyone else.
And do we really have to accept that thin is the only attractive body type? Because even some modern cultures don't accept thin, and prefer fat, so attractiveness is to do with cultural expectations, not some innate Neanderthal hard wiring to seek the best mate.
I think that for younger men there is a greater expectation of having a six pack (eg the scene in Crazy Stupid Love with Ryan Gosling), but by their mid 40s it's OK to see men carry a bit more weight - it almost adds some gravitas. But look at the images of women in that age range. Think about the typical news anchors.
In reality, men are about 10% bigger than women on average - which means that the vast numbers of men and women overlap, yet we have this absolute fixed image that a woman should be smaller than a man, and box office takings are bigger the greater the height gap between a male lead and a female co star.
There's loads to this, but I will shut up for now.