I have a friend, who I am not identifying because their medical world is their own damn business, who is allergic to fructose. Eating too many "healthy" fruits and vegetables could legit kill them.
They have a kid, and the kid has the same condition. So a healthy snack for their child is not grapes, it's chicken nuggets or popcorn. Even carrot sticks have too much of the bad sugar.
I am low-carb for medical reasons. I know other people with the same condition I have who react much less severely to complex carbohydrates, and can make different food choices. Me, if I budget for a slice of pie or whatever, I am signing up for a six-hour migraine.
When I say "I can't have that, it's bad for me," I'm not saying it's sinful, or naughty, or you can't have it. I'm saying it will do me active damage, and so I am being careful. I am strict and precise with my diet, and I choose my treats based on how much pain they're worth.
No one else gets to look at me and decide whether I'm eating a healthy diet. I mean, my doctor, my nutritionist, and my therapist, they all get a say. But I know how foods make me feel, and I know which foods upset my physical form, and I guide my choices based on that knowledge.