I don't agree with that.
From my own experience losing weight is not easy, despite having the motivation of a gorgeous attractive man. It's an awful experience for most people and feeling you have to improve yourself for someone is an incredible pressure, and rarely if a person thinks that way will they ever feel deserving of said attractive partner, no matter how much they change themselves physically.

A good friend once said to me something along the lines of 'this is the way I see it: the exterior is gonna change, but what's inside stays the same.'
He's right.

There's a guy I know, and y'no I wouldn't care if it turned out he was a midget, or very overweight, or physically disfigured in any way, I'd still think he was hot and extremely shaggable, because the exterior is just that- an exterior.
Looks do count, but only in being physically and carnally attracted to someone. People's tastes are different. Like I'd swear my bum was too big, but blokes have adored it, despite my insistence on them getting their eyes tested.

Women are often more sensitive about their appearance than men. You want big boobs, but the price to pay for naturally big boobs is a belly or large thighs. You have a flat stomach, but you're bony and uncomfortable.

I think a final thing is when you truly care about and love someone you see them completely differently to how a stranger sees them. Things like a bit of cellulite on the thighs or a squidgy tummy or an excessively large forehead or a hairy back don't matter so much unless you're looking for a trophy boyfriend/girlfriend.