In 1920 Newburgh and Squier1 reported the occurrence of atherosclerosis in rabbits fed diets rich in animal protein. The diets used were of two kinds: one was a mixture of milk, scraped carrot and water to which casein was added; the other was a mixture of dried powdered beef and bread flour in the proportion 1:2. Although it appeared that the vascular lesions had been caused by the protein of the diets, such a conclusion was thought not to be warranted at that time because of the smallness of the group of experimental animals.
Later, investigation by Newburgh and Clarkson2 showed conclusively that ingestion of muscle meat by rabbits results in extensive atherosclerosis of the aorta and other large arteries. Eight of eleven animals that were fed a diet containing 27 per cent protein derived chiefly from dried ground beef muscle for more than six months became atherosclerotic.
FREYBERG RH. RELATION OF EXPERIMENTAL ATHEROSCLEROSIS TO DIETS RICH IN VEGETABLE PROTEIN. Arch Intern Med (Chic). 1937;59(4):660-666. doi:10.1001/archinte.1937.00170200102008