PHILADELHPHIA — Protests aside, there may be another reason to pass on the foie gras. Scientists report that these livers of overstuffed waterfowl contain abnormal proteins that, when fed to laboratory mice, caused them to quickly develop the protein clumps themselves.

Various human diseases — among them Alzheimer's, Parkinson's, and rheumatoid arthritis — are associated with these clumps, known as amyloids.

The new paper, published last week in the Proceedings of the National Academy of Sciences, provides no direct evidence that people are in danger. But the researchers do suggest that some people avoid indulging.

Foie gras is a traditional food in France and throughout Europe — where, interestingly, amyloidosis is more common than here — but arrived on the American culinary scene in the 1990s.

So why is this heavy, fat-rich delicacy also rich in amyloids?

Put simply, force-feeding makes animals sick. To produce the succulent livers, tubes are inserted into the birds' throats and corn mush is pumped in, massively inflating the animals and making them tasty.

When animals are stressed for any number of reasons, their livers go into overdrive, making more of a specific type of protein that is linked to inflammatory rheumatoid arthritis. If the stress is prolonged, the excess protein may build up and bunch together as amyloids — first in the delicious fowl liver, then elsewhere.

Human livers, too, can be overwhelmed by amyloids in conjunction with chronic inflammatory disorders.

Each amyloid disease involves the clumping of a different protein. Alzheimer's amyloids don't match arthritis amyloids, for example.

Before they form amyloids, however, these proteins are often part of a normal, healthy organism. It is only when normal proteins encounter contagious abnormal proteins such as those now found in foie gras that things may go south.

"They get into vital tissues and compromise the function of that organ," said Alan Solomon, an internist at the University of Tennessee and the study's lead author.

Solomon said neither he nor his colleagues have any connection with animal rights groups. Nevertheless, for animal rights groups already at odds with foie gras, the scientific evidence may sound too good to be true.

Activists believe force-feeding animals is cruel. In Chicago, restaurants can no longer serve foie gras. California has outlawed it, effective in 2012. Foie gras is banned in all of Israel. Philadelphia, too, is considering taking a stance on the issue. City Councilman Jack Kelly's bill prohibiting the sale of foie gras is currently in committee.

The amount of foie gras given to the mice would equal about 3 1/2 pounds over five days for humans, Solomon estimates. This may seem like a lot, especially considering that even in France the annual consumption is about half a pound.

Yet evidence suggests that it takes very little of the protein clumps to instigate amyloidosis — and that amyloids, rather than being digested, may just lurk about until there are enough to cause disease.

— Distributed by McClatchy-Tribune Information Services