A study on the Purina site:
http://www.purina.com/institute/news.asp?article=421

and an article in DVM Magazine:
http://www.dvmnewsmagazine.com/dvm/a...l.jsp?id=26745

and more on body fat and health problems:
http://www.dvmnewsmagazine.com/dvm/a...l.jsp?id=81753

Here's a pdf of the body condition scale:
http://www.purina.com/images/article...yCondChart.pdf

Here's a pdf of the body condition scale for puppies:
http://www.purina.com/images/article...yCondChart.pdf