Question: Can too much protein be harmful?

Protein poisoning


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 near complete absence of fat in the diet.
Excess protein is sometimes cited as the cause of this condition, however 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 2kg (live weight). Based on a carcass yield of 60%, rabbit meat is around 8.3% fat[1] while beef and pork are 32% fat and lamb 28%.[2]
Possible mechanisms
Given the lack of scientific data on the effects of high-protein diets, the US Food and Nutrition Board does not set a tolerable upper intake level nor upper acceptable macronutrient distribution range for protein.[3]
Observations
In U.S. Military Arctic Light Infantry Training (ALIT), it is taught that rabbit takes more vitamins to digest than it returns.  It is recommended in survival situations to refrain from eating at all if rabbit is the only thing to eat.  Though, instead of eating the meat (which consumes your fat and vitamins), you could simply boil the rabbit meat to extract the fat and some minerals and vitamins (some vitamins will be destroyed by temperature).  
The Arctic explorer Vilhjalmur Stefansson, who experienced rabbit starvation himself, 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.[4]
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.[5]
In Into the Wild (1996), Jon Krakauer conjectured that Chris McCandless might have suffered from rabbit starvation.
See also
Country food/Inuit diet, the traditional diet of the Inuit and First Nations
Kwashiorkor – Disease resulting from sufficient caloric intake with very low protein content
Marasmus – Disease caused by inadequate caloric intake
No-carbohydrate diet
Protein toxicity – damage caused by buildup of protein metabolic waste products in the bloodstream
Proteopathy – damage caused by misfolded proteins


Further reading