Paphian
My Wife is diabetic, and we have never had a problem, declare it at security.
On one occasion the stewardess offered to put the hand baggage in the locker and my wife said she needed to keep her food near her as she was diabetic. the stewardess wanted to know all about it in case there was a problem in flight, although my Wife assured her she would be alright.
A tip we picked up some years ago from this site is a product for insulin by Frio Insulin cooling case, they come in various sizes for on or more pens and have a reusable cool pack inside, just soak it and freeze. which keeps cool for a long time. If you Google them the company is very helpful and reasonable. we would not be without one
Hope this helps