https://www.employmentlawwatch.com/...ed-by-diet-is-not-automatically-a-disability/
but.
"This is an interesting and potentially important decision. Type 2 diabetes is by far the most common type, with 90% of approximately 3.1 million diabetics in the UK having type 2 diabetes. This case illustrates the fact that even where a medical condition is clinically well recognised, that in itself is not sufficient for it to be a disability. This case will also likely make it harder for people suffering from nut allergies, lactose intolerances, etc., who manage their conditions by avoiding certain foods/drinks, to claim that they are disabled. Note that the EAT accepted that medicated diabetes sufferers (type 1 or type 2) are regularly considered to be disabled for the purposes of the Equality Act."
So it seems if your condition is controlled by diet alone than no it does not qualify but if you are medicated then yes it does.