Vitamins for men

I can’t understand why inspite of the fact that my husband eat a lot very often he’s still not getting any weight gain. So i told him maybe it’s about time that i should look and buy the best vitamins for men. He agreed only if the medicine will not just increase his weight but will also build his muscles. I told him i already read something about body building and a weight gain at the same time. Hopefully i can find something the one hes’ looking for soon.