RTÉ presenters Miriam O'Callaghan and Kathryn Thomas have found themselves unwittingly endorsing unproven diet products in Facebook ads.

The ads on the social networking site feature images and comments from the broadcasters with links to sites promoting weight loss or diet supplements.

A photo of O'Callaghan has been appearing in an ad which says "Miriam Melts Belly Fat? She got skinny fast by following this new 'green' tip, no crazy diet or exercise."

Never endorsed
The Prime Time host said a number of people had contacted her to say her image was being used in this way on Facebook and other places online, adding that she never endorsed any such products.

“Someone acting on my behalf did try to get them taken down as I obviously never gave my permission for my image to be used in this way, but to no avail, clearly, as they are still up.”

Operation Transformation star Kathryn Thomas has had her name and image used in a similar way.

Her photo features alongside a Facebook ad with the statement: “Kathryn melts belly fat? She lost weight quick, easy and healthy with no crazy exercise! Now her weight loss tips have finally been revealed.”