I'm going to get downvoted to hell for saying this, but instead of "not letting the world make you feel bad about yourself" you could also harness that negative feeling as a motivation to do something about it.

Because being overweight is not you being the best version of yourself. Your health, energy, romantic life, and likely even career would improve if you did something about the problem. It is something that's entirely within your control to do something about.

Life is short, it's too short to spend it fat. The best time to take action is now.

Practically everyone finds fat people less attractive. Lying to them about their prospects will only cause cognitive dissonance when the truth eventually presents itself.