I replaced self harm with eating and my weight has gotten out of control, what can I do?

Get therapy. Your body is like a vehicle; it gets you around. You would never overfill your car or give it diesel when it needs regular fuel. If you are using food instead self mutilation, you continue to hurt yourself, just in a different way. It is important to get to the source of the problem instead of just focusing on the symptom (self mutilation or overeating). Seek professional help.
Eat low calorie food. One can switch to low calorie foods and try running or jogging. Jogging is a good way to lose weight, as long as one doesn't eat snacks, energy bars, or drink sugared drinks while jogging. Weight will only be lost if the calories burned during jogging exceeds the calories eaten or drank by the jogger. One should continue seeing the doctor or psychiatrist for medication and/or mental health issues.