If you know Tim then you know his methods are purely for marketing. Tim has been much bigger and muscular in the past.
It was said by a multitude of readers that he purposely lost weight in order to regain it just for the book so that he could technically say he gained x weight in x time.
It worked for Tim. The guy is a brilliant marketer. As far as the legitimacy of this claim, it is tainted.
His book "the 4 hour work week" is a good read. It tells you nothing which you cannot find through searching on the inet but it is interesting such as hiring vitrtual workers to perform basic tasks that you have, hiring upstart cleaning agencies to do menial tasks around the house.
It was all purported to help squeeze more time out of your day in order to have time for familiy and to make your life more efficient while creating financial stability.