"The other way to look at it is that he might be an expert..."
He is definitely an expert. From Wikipedia, he is a pediatrician, co-inventor of a rotavirus vaccine, and published more than 130 papers in medical and scientific journals.
Medicine is a very big field. Indeed, so big that being a pediatrician, co-inventor of a rotavirus vaccine and publishing 100-odd papers doesn't make someone an expert on the very specific topic of human use of antioxidants. That is, unless the 100-odd papers are related to the human use of antioxidants.
He is definitely an expert. From Wikipedia, he is a pediatrician, co-inventor of a rotavirus vaccine, and published more than 130 papers in medical and scientific journals.
http://en.wikipedia.org/wiki/Paul_Offit