I find the more you explain, the less awesome it is. The story should be first and foremost about your characters, and the more detail you add to the book, the more it gets bogged down. Sanderson's books worked for me, but I must admit the thing that brought them crashing down . Out of what I've read (Mistborn, Alloy of Law, ** I preferred Steelheart a lot more because he doesn't tell me how exactly it all works; he leaves enough to the imagination that the system works, but it generates plot even just as the protagonist tries to work out the weaknesses of each Epic.

What you're looking for in writing a book:

• a magic system that works coherently. You apparently have that; you just need a detail or two.

• interesting plot, characters and setting.

• a book which reads well; that is, the reader doesn't have to know the fine detail of how it works unless it's immediately relevant. The metals in Mistborn were introduced one by one. That seems the best way to proceed; one of the things that makes Sanderson a good writer is that he doesn't infodump that much and so as much as I think his magic systems don't need to be so contrived, he's done a lot right in telling the story.

How are you writing your calorific magic? How do you deal with the idea we all need calories for mundane fuel, and how does the magic system distinguish between eaten calories, and calories used for magic? How does a human body differentiate? I think the more specific you get, the more these kinds of questions arise, whereas treating magic as less 'scientific' means you don't have to explain much beyond the ritual the wizard performs to establish the chalk circle.

To me, the metal stuff in Mistborn didn't make sense because the characters ingested the metals and burnt them in their stomach. Sounds dangerous and weird and a bit contrived to me; I do prefer it if magic remains esoteric and supernatural. And then you're doing something relatively conventional, a demon-summoning, which a lot of people have seen before and accepted as just the product of undefined hocus-pocus.

This is why I'm saying that really, less is more. The more you seek to define and explain, the less interesting magic gets, and the more you have to answer. I can't give you any specifics about demon-summoning, but most people wouldn't need to get highly specific, and I think that's your answer there.