I have an (attention-seeking) occasional visitor who behaves as if she's a famous health and fitness guru. Diet is her area of expertise - it would seem - her specialist subject.
She declines all sugar/carbs, caffeine, tap water, fatty and/or processed food - yet seems to dislike fruit, veg or beans. Her body is a temple, apparently.
Why then, you might ask, is she constantly suffering from some minor illness (real or imagined), overweight, depressed, out of breath with high BP?
I think it's health anxiety - along with a firm conviction that she's somehow special and different - not like other people.