Conflicted about food

So my son had his 4 month check up. We got the go ahead to start solids now. The pediatrician wants him to do oatmeal or rice cereal for the first 3 weeks. The after that we can start purees. He doesn’t want us to do purees first because he wants him to get use to eating solids with cereal. I told him that cereal constipates him extremely bad because we had to do it before when they were trying to help his silent reflux. I hate cereal because it has no nutrients in it. Has anyone by passed cereal and went straight to solids at 4 months