I can think of better things to eat than chocolate and snacks as a diebetic. I rarely eat chocolate, maybe the odd mars bar once a fortnight or so as a treat. Fruit, though it does contain natural sugar, is so much better for you.
Your employer sounds like a tosser, by the way. How come they have it in for you, has it always been this way?
I had a new boss once who took an instant dislike to me. He was on my case all the time. You're entitled to short breaks by law, eg: comfort breaks, refreshments, etc. If not then your company is barbaric, yet you say others go in large groups. Why not join them? If you're not allowed, then you have a case for discrimination, harsh as that may soundam your boss would be in a pickle if he says "you guys carry on ahead, the diabetic, get back to your desk" as you will need regular food intake more than the non-diabetics. As the mantra stipulates, "little and often"
Good luck there, pal.

. (Sock it to 'em and please feedback any outcomes to the group as this is a highly important issue that could affect a lot of people on here)
MW