I would imagine he uses a variety of "sources." I'm sure some of it he just makes up. It's really how he sells it that makes it such a scam. He really knows how to make a believer out of people. Here are some comments from a corresponding Stossel article
Of course, mosts of his cultists use straw man arguments that slam Kevin's detractors for getting on him for writing a book about living a healthy lifestyle. Nevermind the fact they are questioning his cures not his writing of a book about a healthy lifestyle.
Here's a comment on his "Debt Cures"
Are you talking about Don Lapre's "The Greatest Vitamin in the World?" I'm not sure who makes these vitamins, but Don Lapre is also a scam artist who could be known as Kevin Trudeau Jr.
Here's a youtube of a Don Lapre spoof.
http://www.youtube.com/watch?v=Nns3He0qYJs
Kevin Trudeau reminds me of Steve Parent
Edit: This should probably say Steve Parent reminds me of Kevin Trudeau, as I'm sure Steve goes to sleep at night dreaming of reaching the levels of "success" that Kevin has "achieved"