Most of us aren't going to react like, "Hey, that's me! She's me! That totally happens to me!" We're going to be like, "What size do you have to move up to now? Zero?"
It's like if they didn't bother to make any CG changes to Chris Evans in Captain America for his scrawny "before" scenes and he was just sitting around in his rippling muscles, complaining about how he wishes he was strong enough to beat up bullies.
It's like having Toni Collette play "the fat sister," as she did in In Her Shoes.
Look at that fat whale. It totally rings true when she frets about her weight. Look, I totally get it that nobody wants to see actual fat people on a screen for two hours and Hollywood has to trot out skinny actresses because that's what the audience wants. But write them some skinny-person parts, then. Don't have them look average-sized female viewers in the eye and basically say, "I know what you're going through! I'm just like you!" That's just silly.