To be colitically porrect, no one is fat. Fat is just that special thing that makes "fat" people fat. Nah, you gotta call 'em overweight or obese.
I have never, and will never be obese. I will not let my self get there. I don't have to much worry though, either. My metabolism is like super fast or something. It's probably slowly catching up to me, but I also work it off with PE, my daily walks to and from school, etcetc. I don't see how anybody could let themselves get obese like that.
To lose weight? Eat healthy, exercise. Instead of grabbing that donut, grab that apple. Instead of getting in your car for work, bring out your bike. Even if you aren't overweight, do that anyway, you'll save yourself, AND the planet. That's a win-win situation, ain't it? You could calculate yourself some big ol' diet, but I wouldn't even bother with that unless you are gonna be a pro bodybuilder. Just eat better and work out more.
If I ever do get over-weight, I would fix that immediately, before I got obese. Sorry, but I'm not gonna be like that. It's gross to me, no offense to anyone. It just shows that you don't care, that you don't try. Which is just about the worst thing that you should do. No matter what happens, I will always have enough self-care for personal hygeine-fitness. I can't say that I care about anything much other than that, tbh. Smoke, drink, tweak, whatever floats your boat, just take care of yourself, aye?