I would just ask him what he wants to eat at the celebration. If he is careful about his carbs, why would he want a tableful of cakes and soft drinks etc, as hard as it is that is YOUR idea of what constitutes a good birthday. You sound like such a good Mum so if you know what he normally eats, just fill the table with salmon/nuts/cheeses/cold meats or hot chicken, low carb coleslaw, etc. Then add the balloons and whatever else (maybe some red wine!), and off you go. I am sure he will really appreciate that you have taken notice of how HE likes to eat. You mention he won't eat even a little bit of cake but why would he?, what would be the point of eating something that his body doesn't agree with, eating it because it is his birthday makes NO sense, that sounds like something other people feel that diabetics are somehow missing out on, believe us when we say we are not.