To a certain extent yes, if you’re lacking proper nutrition, not getting enough sleep, sleep apnea, stressed, i.e. if you have something that’s impeding your intelligence you have room to improve.

I.E. studies of economic vegetarian children showed tremendous cognitive improvements when supplemented with one egg a day. They lacked proper nutrition

The impact on a fully developed adult brain could be just as impactful depending on the problem, but probably would be more subtle