How can a 5'4 143 pound 12 year old lose weight?

First, that is a tall 12 year old. I am 28 5'5 and weigh 135lbs. Best thing to do is regulate his/her diet, take a daily vitamin & stay active. Take walks, play basketball, swim, go jogging.

If you're a parent, get involved, get in shape yourself!

Now, you'll notice an apetite increase with all the activity and that's normal, your body needs to replace the energy. Drink a lot of water and no sugary drinks!