I agree with mmm

Pottassium is not found in bananas in the elemental form, which is very reactive. It is instead found as a salt. Possibly as KCl or the salt of an organic anion.

Look at it this way. Pottassium is so reactive, that it already reacted with something in the banana and formed a very stable potassium salt. So it doesn't react with HCl in the stomach.

This stands for all other metals that the body requires, I believe. They do not come in elemental form.