Fast Metabolism

My metabolism used to be super fast & I was super thin, TMI but pooping minutes after just had eaten, then eating again, and you know, pooping again. I would poop very fast, and I guess that helped me stay really rod thin since I would eat fast-food and junk, but anyways now I’m bigger & my metabolism is a lot slower. Soo basically, does anyone have any tips or really good food ideas that will fasten up my metabolism that I could eat or take regularly ?

I want to LOOSE weight not gain weight.