Save yourself a lot of money and buy this book. She is a nutritionist and explains everything you need to know. If you are a high end athlete, this won't be what you are looking for, but if you are just looking to understand more and eat healthier than it will be great. Ignore the diet part and just take in the knowledge. She has lots of other good books that may be better suited to your needs.
No Fail Diet
Leslie Beck
http://www.chapters.indigo.ca/books/...fail+diet'