system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does my body need various metals like zinc, iron, manganese, etc? How does my body process these metals?
gpt
What the layman understands as 'metal' with 'metallic' properties (a certain look, feel, taste, electrical conductivity etc.) only exists when there are large quantities of the specific metal atoms that form special metallic bonds. 


In the body, where metallic atoms are required in very very small quantities ('trace elements'), they are usually present in single-atom form and thus do not show any 'metallic' properties. As single-atom elements, they perform duties much like any other element that you need to survive: Because of their specific properties and interaction with other elements, your body uses them in the construction of specific proteins with specific forms and functions. An iron atom, for example, makes it easier/possible for a protein to bind/unbind oxygen atoms, therefore iron atoms are used in the construction of hemoglobin, the protein that transports oxygen in your blood. 


Because our supply of trace elements usually comes in the form of other organic material, they are already present in single-atom form, so the body has no need for mechanisms or enzymes that break down metallic matter (although some exist). That's why metals aren't considered foodstuff, and you don't crave for them, even though your body needs some of the atoms they are made of.