Is there a correlation between bad diet and IQ drop? Do things like lions mane only help recover what was lost, or can a good diet and supplements give you what you never had?

I was fed lunchables and cereal growing up and it is only in the last couple years I figured out how bad my nutrition was. I thought feeling like you were in a dream state if you were awake more than 10 hours was just normal lol. Brain fog gone, etc. Are there any supplements I can take to help me? Can I recover anything I was robbed of, if bad diet made me dumber than I should have been? I know there was a board on nootropics earlier but it's gone now