According to the US consumer protection organisation, these companies are making unsubstantiated and exaggerated claims about their products.
David Vladeck, director of the FTC's Bureau of Consumer Protection, said: "Almost everything about these sites is fake, the weight-loss results, the so-called investigations, the reporters, the consumer testimonials and the attempt to portray an objective journalistic endeavour."
In 2009, Trading Planet, an online company operated from West Lothian, was banned from promoting its Acai Berry and Colon Cleanse products.
The Advertising Standards Authority (ASA), which had investigated claims made against the company, ruled that the company provided no evidence that its products helped boost weight loss.
The ASA also stated that the company had failed to make it clear to customers that they would be automatically charged by the company once their free trial had expired.