Personally I think this is a dicey topic. I’ve seen a few students attempt to execute it, and they all were either a) basically fat shaming (because “I did it with incredible impulse control and now I’m skinny and happy!”–the implication is that fat people Just Don’t Want It Enough And Are Miserable) or b) revealed that, actually, the writer had an eating disorder but didn’t recognize this (this happened with one girl and it took all my strength not to beg her to go to therapy. Orthorexia is a thing and all that.). I’m not saying you would do either, but letting you know what I’ve seen that has raised my hackles. Personally, as a fat person, if I were an admissions officer, an essay on weight loss would put me on guard and the above red flags would make it a “no” for me. Just an example of how an admissions’ officer’s personal biases may come into play with your essay.
So that tells you what to avoid. But my question: is this the most interesting thing about you?