Protein poisoning (also referred to colloquially as rabbit starvation, mal de caribou, or fat starvation) is an acute form of malnutrition caused by a diet deficient in fat and carbohydrates, where almost all bioavailable calories come from the protein in lean meat.^[1][2] The concept is discussed in the context of paleoanthropological investigations into the diet of ancient humans, especially during the Last Glacial Maximum and at high latitude regions.^[3][4]

The term rabbit starvation originates from the fact that rabbit meat is very low in fat, with almost all of its caloric content from the amino acids digested out of skeletal muscle protein, and therefore is a food which, if consumed exclusively, would cause protein poisoning.^[4] The reported symptoms include initial nausea and fatigue, followed by diarrhea and ultimately death.^[4]

Observations

In Appian's Roman History, Volume I, Book VI: The Wars in Spain, Chapter IX, page 223, the author notes a multitude of Roman soldiers dying of severe diarrhea after eating mostly rabbits while besieging the city Intercatia in approx 150 B.C. Appian wrote:

... strange terror in the Roman camp. Their soldiers were sick from watching and want of sleep, and because of the unaccustomed food which the country afforded. They had no wine, no salt, no vinegar, no oil, but lived on wheat and barley, and quantities of venison and rabbits' flesh boiled without salt, which caused dysentery, from which many died. ^[5]

The explorer Vilhjalmur Stefansson is said to have lived for years exclusively on game meat and fish, with no ill effects. The same is true for his fellow explorer Karsten Anderson. As part of his promotion of meat-only diet modeled on Inuit cuisine, and to demonstrate the effects, in New York City beginning in February 1928, Stefansson and Anderson "lived and ate in the metabolism ward of Russell Sage Institute of Pathology of Bellevue Hospital, New York" for a year, with their metabolic performance closely observed, all this partly funded by the Institute of American Meat Packers.^[6] Researchers hoping to replicate Stefansson's experience with rabbit starvation in the field urged him to cut the fat intake in his all-meat diet to zero. He did, and experienced a much quicker onset of diarrhea than in the field. With fat added back in, Stefansson recovered, although with a 10-day period of constipation afterwards. The study reported finding no previous medical literature examining either the effects of meat-only diets, which appear to be sustainable, or on rabbit starvation, which is fatal.

Stefansson wrote:

The groups that depend on the blubber animals are the most fortunate in the hunting way of life, for they never suffer from fat-hunger. This trouble is worst, so far as North America is concerned, among those forest Indians who depend at times on rabbits, the leanest animal in the North, and who develop the extreme fat-hunger known as rabbit-starvation. Rabbit eaters, if they have no fat from another source—beaver, moose, fish—will develop diarrhea in about a week, with headache, lassitude and vague discomfort. If there are enough rabbits, the people eat till their stomachs are distended; but no matter how much they eat they feel unsatisfied. Some think a man will die sooner if he eats continually of fat-free meat than if he eats nothing, but this is a belief on which sufficient evidence for a decision has not been gathered in the North. Deaths from rabbit-starvation, or from the eating of other skinny meat, are rare; for everyone understands the principle, and any possible preventive steps are naturally taken.^[7]

A World War II-era Arctic survival booklet issued by the Flight Control Command of the United States Army Air Forces included this emphatic warning: "Because of the importance of fats, under no conditions limit yourself to a meat diet of rabbit just because they happen to be plentiful in the region where you are forced down. A continued diet of rabbit will produce rabbit starvation -- diarrhea will begin in about a week and if the diet is continued DEATH MAY RESULT."^[8]

Physiology

The U.S. and Canadian Dietary Reference Intake review for protein mentions "rabbit starvation", but concluded that there was not sufficient evidence by 2005 to establish a tolerable upper intake level, i.e., an upper limit for how much protein can be safely consumed.^[9]

According to Bilsborough and Mann in 2006, protein intake is mainly restricted by the urea cycle, but deriving more than 35% of energy needs from protein leads to health problems.^[10] They suggested an upper limit of 25% or 2-2.5 g/kg, "corresponding to 176 g protein per day for an 80 kg individual", but stated that humans can theoretically use much larger amounts than this for energy.^[10] For arctic hunter-gatherers, the amount can seasonally increase to 45%.^[11]