I used to buy lots of books too; but don't anymore. I have a good book now that is helping me more than any other book as far as food is concerned --called "FOOD TO IMPROVE YOUR HEALTH" and I am sure there are others out there like it. I didn't pay a cent for it -- my mother picked it up for 10c at a second-hand bookstore, no less ...
I am more wary now; and go on the net and do a search for reviews like the above poster said. I read what others think first before wasting any more money. I find some plans are too strict, or too judgemental of the user, so they are a waste of time and money for me. If I see a review and comments that help me, then I may fork out the money on a very rare occasion.
For instance, I like many of the ideas from "The Beck Solution" book and there are many threads here that you can read all about it. I made up my own eating plan based on my own research and experience; a plan that suits me, my body, and my lifestyle ...