Foie gras is a diseased liver and is loaded with saturated fat and cholesterol. Dr. Michael Greger found that "microscopic infectious protein fibers in foie gras may trigger and accelerate a variety of serious human diseases in susceptible individuals via a 'mad cow disease' - like mechanism." The full report, which was published in International Journal of Food Safety, Nutrition and Public Health, is available here.
A collaboration of researchers found deposits of amylodosis - a group of potentially fatal diseases - in commercially available foie gras. A report on their findings, which appear in Proceedings of the National Academy of Sciences, can be read here.