I am a 68 year old retired R.N. and purchased this book two days ago. I have not read the entire text, so you may wonder why the five star rating. The reason is this. At the very beginning of the book, there is very illuminating information about motivation and habit formation. Believe me when I say this information has given me my own PERSONAL REASONS to enter into a fitness/health program. Motivation has always been my one, and most glaring obstacle to achieving optimal health. I applaud the authors in recognizing this very fact, and for addressing the issue with insight and understanding at the very beginning so the reader is armed with the answer to "why am I doing this" question. If one doesn't have a ready answer to that, any program is due to fail. So, pull this book off the shelf, glance at its sensible, and well-researched pages, and buy it. Never before have I had tangible ways to get motivated towards a healthy lifestyle. Thankyou, Doctors