Sorry to break it to you but there is no such thing as a healthy slice or cake!! The best way to consume sugar is in it's natural state, in fruit.

I hear your pain though. When pg I fell into a terrible energy slump and was on a constant sugar roller coaster. It is a terrible self perpetuating cycle and fruit just didn't cut it. Since my birth, it kept going, but I found some great inspiration and answers in the book 'Sweet Poison' which has helped me give up Sugar. Fruit is plenty sweet now that I don't eat the processed stuff.

I recommend looking for the book. You could also have a chat to a Chinese doctor or a natural therapist to help you kick the sugar habit. They can have great gentle ways of getting you body back in balance.

BTW, all the best with the HBAC!! I had one last year which was awesome.

ETA: for more practical advice, try also to keep things like nuts around for an energy fix and try to have a glass of water or a banana for a fix before reaching for the chocolate.