Baby food with rice or oatmeal?

My son is a pooper! Goes 4-5 times a day due to his formula. He is on Similac Alimentum. We started baby food. I mix it with oatmeal but I'm thinking of switching to rice to maybe help him poop less? He isn't bothered by pooping or doesn't get diaper rashes...is this number of poops normal and should I try rice opposed to oatmeal? He is 4 months.