One factor among hundreds. There's many way to counter the effects of slowed metabolism as well it's not the only thing we're dealing with here. Obviously exercise and diet are the two factors people could control the most but in your other comment you recommended testing for heavy metals in people and using methods to reduce it which I'd fully support if I were POTUS. You're still not going to magically get thin if you get rid of heavy metals though. You need exercise and diet.