I’m writing my essay for the common app using the prompt asking what is one problem that I’ve solved.
I used to be overweight, when I was a sophomore, I lost 50 pounds, (the healthy way, not anorexia)
I’ve mostly written my essay but I’m unsure what direction the essay should go in, what are some things I should be sure to highlight and what are things I should avoid? Any suggestions?
First off congrats that’s a really big accomplishment! Obviously don’t spend the whole essay going over what you ate everyday and how much you exercised. Just give a brief overview then focus on what you learned form it, how it changed you, made you into who you are today etc etc. I’m sorry I don’t have much advice but just wanted to say congrats 
I’ve seen it done successfully.
Go for it! Sounds like it’d be a interesting and unique essay.
Does it tie into your future plans or research interests at all?
Weight loss is a very common topic among every generation.
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?
People that say an essay should tie into your major or something you are planning your life around do not know what they are talking about. If you can write about something that reveals an aspect of yourself which is interesting, then that is what counts. It doesn’t even have to be the “most” interesting thing. You are not on a psychiatry couch. The purpose is solely for admissions to feel some connection to you and to see that you can communicate effectively.
People that say an essay should tie into your major or something you are planning your life around do not know what they are talking about. Agree 100%
Echoing the above two comments. You want the essay to be personal, meaningful and be able to tell admissions officers something about yourself that they would not get elsewhere in the application. I would highlight what you leaned, how you changed etc. as a result of your journey.
One more time for good measure.
An essay should be a way for the reader to know you better (and like you better and want you on their campus) when they have finished reading.