Ugh... I'm trying REALLY hard not to blow this up... So I'm gonna try and keep it civil.
Real quick... What is one right that men have that women don't in the USA in 2015? Feminists I ask tend to hand-wave and lay on the ad hominem attacks. No one answers, probably because there IS no answer. They aren't denied anything.
Second, the dictionary definition of feminism vs the actual, demonstrated, definition are two different things.
You say accepting being fat seems like the antithesis of feminism. Well, depends on which definition you subscribe to. If you talk about first- and some of second-wave (prior to all man-hate), then yeah, I could see that. If you talk about latter second- and into third- and now fourth-wave, then it falls PERFECTLY in line.
How? Simiple. Current "party line" of feminism is simultaneously, "Women are strong!" and ALSO "Women are perpetual victims!!" This is why SJW cling to it so tightly. It's no more about equal opportunity, but instead equal outcome. All the benefits; none of the responsibilities.
Let's look at two areas... If a man has a SINGLE drink, he's still held accountable for his actions. If he consents to sex with a sober woman, he's still responsible for his actions. If a woman has a single drink and consents to sex with a sober man, then later (2, 3, 7 days?) regrets her decision, she can file rape charges. She can claim perpetual victim status. This is the law that was just passed in CA, in case you wondered. The affirmative consent law. The scenario I just described has happened, it's not something I just made up.
Next area, careers!! By now we all know the "wage gap" is a myth. Let's not argue that. The feminists move that women should be paid the same amount as men, even if they work fewer hours, take more vacations, and have less experience. The idea being that women should be able to take time off to have children or other life decisions and not have it impact their earning capacity. You see? Strong, but perpetual victims.
This is why it's SO SO SO attractive to couple feminism in with fat-acceptance and SJWism. Those two groups of people live the life of perpetual victims and want nothing to do with responsibility. They're also most frequently women, as I'm sure you know.
Damn, this ended up long-winded anyway. Sorry about that. I'd like to clarify that I think women should absolutely have the same rights and opportunities as men. And they do. The feminists I respect and support (Christina Sommers, Karen Straughen, Erin Pizzey, etc) are rejected by today's feminists because they don't tow the "I am a victim" line. They can do what men do, but they don't shirk the responsibility. They understand what hard work is and that it's required.
Edit: As an exercise, go out and talk to people you identify as feminists and see how they respond to things like the prison population being 90+% male. With women making up half the population it's laughable to think they only commit 10% of jailable offenses. Also ask about the jobs no one wants: Sewage workers, garbage men, miners, police, fire, etc. Why are they male-dominated? Seems like feminists only care about getting women into the easier white-collar jobs (STEM). There's been no vocalization the other industries I've mentioned.