Having gone through this somewhat, I'd place the blame more on them if there was any.
I dated a feminist vegetarian last year. Said she's a vegetarian, but she had no problem eating "my meat" at night
. She was cray cray though, and had plenty of excuses to why she was getting fat. She was able to get away with it because her tits were fairly large to it distracted the eyes from the gut, but a few months in... there was no saving this. Eyes deviated and saw the behemoth of the gut that was growing. I actually thought she was pregnant, then I realized she was just fat. The best was "I have a stomach problem", okay doll, you're fat cause you eat massive servings of spaghetti and nuts that would make a 240lb athlete fat.
It was funny of her telling me how to diet and eat. Me, the guy that is highly active, competes, trains in combat sports, and have been through quite a bit of cutting cycles is getting told I'm wrong about how this all works because genetics. lol
She got even fatter after we stopped dating. Ended up being 170ish @ 5'3. lol