How do i slow my metabolism down. i have a extremely fast metabolism and i would like to gain some attractive weight. what is the best way to do this?

Muscle training: You will want to use your metabolism to your advantage. Would research and develop a weight training program to develop muscle mass in the correct way. You will also need smart amounts and type of protein intake as building blocks for muscle. Classical weight moves of squat, deadlift, and benchpress, done properly will help in initial structural development. Use a professional trainer to start.

Do no harm: There is a general rule in medicine which should be adopted by humanity. First do no harm! you do not have a disease or medical condition to stop or change. Any attempt to change this would be taking unnecessary risks to your health. Perhaps your journey in life is to learn to love yourself as you are.