As far as I know, studies do not show any health benefits to food that is labelled organic. One reason is that the label of organic is more about marketing and industry than about health. The work of Michael Pollan is very good on this subject, especially Omnivore's Dilemma.

I would not compare an interest in organic food to a gluten-free diet. I would be careful when saying '"gluten-free" craze' because celiac disease is very real and certain people cannot tolerate gluten. I am not saying the subject is out-of-bounds, but just be informed before discussing. Personally, I find trying to understand other people's diets to be a subject that is best avoided and I would not get into it with your friend.