dentist’s advice with food

hi. i’m 24f and don’t have any medical problems except mental health issues (depression and an eating disorder).

i went for a 6-month check up with my dentist who did x-rays of my teeth. there is enamel decay in between my molars (early stages) and if it gets worse, i’ll need 6 fillings.

she asked about my dietary and drinking habits, and told me to cut out anything sugary and acidic, and to stop snacking. i asked if fruit was bad because of the sugar, and she said if i am going to have fruit, have it as a meal and to not graze on it.

because of my eating disorder, i’m kind of spiralling because of this. my gp wants me to gain weight since my bmi is 14.8, but i don’t know how to do that with cutting out more food. i know i don’t eat healthily since i do eat a lot of sugary snacks, fruit and acidic (sugar-free) energy drinks/soda, but i feel awful being told this when gaining weight is already so hard mentally. i don’t make myself vomit so i know the enamel damage is from my diet.

how do i gain weight like this? after this appointment, i don’t want to eat anything. i feel so guilty for having sugar-free soda just before. i know enamel is impossible to get back so i am panicking.

i don’t know what i’m asking. is it possible to have a healthy relationship with food with cutting out sugar completely?