I've found this A LOT with my colleagues mainly. Telling me that I can't eat things, or even telling me I couldn't take part in a 10k charity run because of my condition (no complaints there though!
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It is difficult because they do mean well, and responding to their "you can't eat that"s with "YES I CAN" seems harsh.
Instead, I've tried educating them on the condition, explaining the proportion of insulin I need to take in relation to carbs etc, explaining the foods and drinks that I absolutely CANNOT have unless I'm having a hypo, things like that. And gradually they've stopped questioning my eating habits.
I find that showcasing your own knowledge on your condition puts the people who care about you at ease. It's scary for them, to think there's something wrong with you when they're fond of you. If they think you're in control and fully understand the condition, they tend to treat you with kid gloves a bit less. (In my experience at least).
I'm also type 1, take metformin and basal and bosul injections
Hope this helps!x