This reminds me of when my older daughter, who was 17 at the time, decided to become a vegan. She's a very smart kid and did her homework on what constitutes a healthy eating plan for a vegan, so I wasn't worried about her. Boy oh boy, though, does she run into some know-it-alls. If I had a dollar for every time she'd heard something like "Are you eating enough protein? You know you need protein, right, even if you're not eating meat?", I'd be rich.
Funnily enough, someone in our family ended up with an iron deficiency - but it wasn't her, it was me. Turns out that now that I don't eat as much red meat, I haven't compensated properly by eating other stuff that contains iron.