He goes into the glands and and hormones that work with (or against) your body in burning fat (depending on your body type), and why they might not be working for you... and most importantly, how to get them to work in your favor. It's a pretty good book, he dumbs down the information so that you can understand it without a biology degree... and it all seems to make sense.
I DO recommend the book, it's cheap on amazon, and it's gotten great reviews on there, as well. He really is all about teaching you how to work WITH your body, to create a healthy lifestyle.
You can also check out his website or take the 'body type' quiz to get the gist of the book. Let me know if you do!