My dad wasn't too supportive of me doing it either, but he knows that in the end I will do as I please. When I got done and told him how much better that I felt, he was pleased and shocked.
Think of it this way, while they are ignoring your information on what could help them out as well, plus tormenting you, you are going to be healthier than they are when you are done. :) So basically you will be one up on them.
But keep up the good work and stay on your fast and ignore their attempts, perhaps buying the book and laying it out on your desk may invoke some conversation, thus teaching them more about it. But once you hit your energy burst, you will be running circles around them and be able to do more work. :D
HH