Protein poisoning (also referred to colloquially as rabbit starvation, mal de caribou, or fat starvation) is a rare form of acute malnutrition thought to be caused by a complete absence of fat.
Contents
Excess protein is sometimes cited as the cause of this issue; when meat and fat are consumed in the correct ratio, such as that found in pemmican (which is 50% fat by volume), the diet is considered nutritionally complete and can support humans for months or more. Other stressors, such as severe cold or a dry environment, may intensify symptoms or decrease time to onset. Symptoms include diarrhea, headache, fatigue, low blood pressure, slow heart rate, and a vague discomfort and hunger (very similar to a food craving) that can be satisfied only by the consumption of fat.
Protein poisoning was first noted as a consequence of eating rabbit meat exclusively, hence the term, "rabbit starvation". Rabbit meat is very lean, commercial rabbit meat has 50–100 g dissectable fat per 2 kg (live weight). Based on a carcass yield of 60%, rabbit meat is around 8.3% fat. For comparison, in terms of carcass composition, beef and pork are 32% fat and lamb 28%.
Possible mechanisms
It has been observed that the human liver cannot safely metabolise much more than 221–301 g of protein per day (for an 80 kg/176 pound person), and human kidneys are similarly limited in their capability to remove urea (a byproduct of protein catabolism) from the bloodstream. Exceeding that amount results in excess levels of amino acids, ammonia (hyperammonemia), and/or urea in the bloodstream, with potentially fatal consequences, especially if the person switches to a high-protein diet without giving time for the levels of his or her hepatic enzymes to upregulate. Since protein only contains 4 kcal/gram, and a typical adult human requires in excess of 1900 kcal to maintain the energy balance, it is possible to exceed the safe intake of protein if one is subjected to a high-protein diet with little or no fat or carbohydrates. However, given the lack of scientific data on the effects of high-protein diets, and the observed ability of the liver to compensate over a few days for a shift in protein intake, the US Food and Nutrition Board does not set a tolerable upper intake level nor upper acceptable macronutrient distribution range for protein.
Observations
The Arctic explorer Vilhjalmur Stefansson wrote as follows:
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.
During the Greely Arctic Expedition 1881–1884, a harrowing experience of 25 expedition members, of whom 19 died, Stefansson refers to "'rabbit starvation' which is now to me the key to the Greely problem," which was why "only six came back." He concludes that one of the reasons for the many deaths was cannibalism of the lean flesh of members who had already died. Stefansson likens this to rabbit starvation, which he explains somewhat as in the above quoted observation.
Charles Darwin, in The Voyage of the Beagle, wrote:
We were here able to buy some biscuit. I had now been several days without tasting any thing besides meat: I did not at all dislike this new regimen; but I felt as if it would only have agreed with me with hard exercise. I have heard that patients in England, when desired to confine themselves exclusively to an animal diet, even with the hope of life before their eyes, have hardly been able to endure it. Yet the Gaucho in the Pampas, for months together, touches nothing but beef. But they eat, I observe, a very large proportion of fat, which is of a less animalized nature; and they particularly dislike dry meat, such as that of the Agouti. Dr. Richardson, also, has remarked, “that when people have fed for a long time solely upon lean animal food, the desire for fat becomes so insatiable, that they can consume a large quantity of unmixed and even oily fat without nausea:” this appears to me a curious physiological fact. It is, perhaps, from their meat regimen that the Gauchos, like other carnivorous animals, can abstain long from food. I was told that at Tandeel, some troops voluntarily pursued a party of Indians for three days, without eating or drinking.
In Into the Wild (1996), Jon Krakauer conjectured that Chris McCandless might have suffered from rabbit starvation.