A federal jury deliberated approximately an hour after a weeklong trial in U.S. District Court in Chicago before finding him guilty of violating a 2004 court order.
Trudeau, 50, of Oak Brook, Ill., had his bond revoked and he was ordered taken into custody by U.S. District Judge Ronald Guzman, who set a schedule for post-trial motions but no sentencing date.
The U.S. Attorney's Office in Chicago said criminal contempt has no statutory maximum sentence.
Prosecutors said Trudeau appeared in three television infomercials between December 2006 and November 2007 in which he willfully misrepresented the contents of his book "The Weight Loss Cure 'They' Don't Want You to Know About."
In April 2010, U.S. District Judge Robert Gettleman issued an order to show cause why Trudeau should not be held in criminal contempt of a Sept. 2, 2004, settlement in which Trudeau agreed not to directly or indirectly produce and broadcast any deceptive infomercials that misrepresented the contents of any book, including the weight loss cure book, the U.S. Attorney's Office said.
Prosecutors said Trudeau, in his infomercials, claimed his book was not a "diet," when in fact it required at least three weeks of eating 500 calories or less a day, and that a hormone found only in pregnant women that was required to be injected daily could be obtained "anywhere," when in fact it could be obtained in the United States only through a doctor's prescription.
Trudeau also claimed that after finishing the diet, consumers could eat anything they wanted without regaining weight, when in fact the diet required severe food deprivation that lasts for life, prosecutors said.
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