What disorder often leads to sufferers eating odd items such as dirt or metal?

This would be known as Pica. Generally pica affects young children, and sometimes, interestingly, affects pregnant women. People with pica have strange cravings for non edible things. This is, understandably, are rare disorder.

Hope this helped! It's a really interesting thing to learn about and I suggest you do more research just for the curiosity of it.

~Just a girl in love with Shawn Mendes