in my experience with lifting weights and being a pothead at the same time i just got bigger and probably put on an extra few pounds of fat...id say not to worry about it harming your body in any way if you are such an active person, just eat healthy like everyone else has said. When i stopped lifting weights (it was a PE class in high school, im now in college) i went from 200 pounds to 160 in a matter of like 8 months, and I smoked a lot more weed in that time so it might make you skinnier, it might just be my metabolism though