I’m studying for a nutrition test tomorrow and I thought I’d procrastinate by showing you guys this. This is straight out of the textbook Nutrition Now 5th Ed. by Judith Brown.
Adults can consume a substantial amount of protein-approximately 35% of total calories-for months at a time without ill effects. This observation is based on studies of the diets of Eskimos, explorers, trappers, and hunters in northern America. The very high-protein diets would generally contain a good deal of fat in the form of whale blubber, lard, or fat added to dried meat. Consumption of 45% of calories from protein is considered too high. Consumption of this level of protein is related to nausea, weakness, and diarrhea. Diets very high in protein result in death after several weeks. (eh?) The disease resulting from excess protein intake was termed “rabbit fever” after it occurred in trappers attempting to exist on wild rabbit only.
High-protein diets have been implicated in the development of weak bones, kidney stones, cancer, heart disease, and obesity. The National Academy of Sciences has concluded that the risk of such disorders does not appear to be increased among individuals consuming 10 to 35% of total calories from protein, and on average adults consume 15%.
A Tolerable Upper Intake Level (UL) for protein has not been established. Because information on the effects of high-protein intakes is limited, people are cautioned not to consume high levels of protein from foods or supplements.
Emphasis added by me.