What should I eat if I am 15 and at the height of 5'1 and want to lose 20 pounds?

Well, I'm just going to assume you want to lose it quickly, seeing as many others would wish to do the same.

From me knowing people who were around that weight and above, my answer is kind of harsh based on what they did.

Don't drink any soda whatsoever. That's sometimes the main cause of peoples' obesity problem, and it definitely isn't healthy. Switch to cold water, and drink as much as you can a day. Even though I'm not overweight, I still refrain from drinking soda and, I only drink cold water--around 11, 16oz. cups every day--and it definitely helps with energy, etc.

Water is what keeps you from becoming highly-famished, even though you'll still be able to tell that you're hungry; the water will definitely help. My philosophy is to drink a cup of water every time you get hungry until, you're no longer feel as hungry. And, when you do eat, don't eat a lot, and make sure it's healthy.

Anyway, the people who I told to just drink cold water, at high amounts everyday and, eat dramatically less, lost about 20-30 pounds in one month. In about 3 months, they lost nearly 80 pounds. All from just drinking water. Of course, they were at a higher weight than that, around 250-280.

So, in truth, you'll probably, possible, start to lose weight slower once you're starting to actually notice the loss. But in truth, it's a gain. And if you keep going, you'll reach your goal in about 3-5 months, possibly. It all depends on how determined you are, how little you eat, and how much you drink.

Good luck with your journey, and stay well.