Both men and women, sick people and healthy people, athletes and couch potatoes, can consume so much protein that they begin to get sick. When the diet provides about150 grams (600 calories) of protein per day, the body begins to convert excess amino acids into glucose and urea. The kidneys, ironically, have to harvest glutamine from muscle or calcium from bone to keep the pH of the bloodstream constant, due to the acidity of the urea released in the degradation of protein. By the time an adult is eating 230 grams (920 calories) of protein per day, essentially all additional protein is turned into glucose and urea, and urea can build up to toxic levels.
Whether or not consuming a lot of protein is toxic depends on two factors:
• Whether the diet also provides fat and
• The presence or absence of certain toxic bacteria in the small intestine.
How do scientists know this?
Early in the twentieth century a Canadian ethnographer named Dr. Vilhjalmur Stefansson lived for over a decade with the Inuit people of Canada's arctic north. For nine of those years he ate nothing but meat and fish, a diet similar to that of his hosts. In his memoirs, Stefansson noted the skepticism of the nutritionists of his day that human beings could survive on protein food alone:
“A belief I was destined to find crucial in my Arctic work, making the difference between success and failure, life and death, was the view that man cannot live on meat alone. The few doctors and dietitians who thought you could were considered unorthodox if not charlatans. The arguments ranged from metaphysics to chemistry: Man was not intended to be carnivorous - you knew that from examining his teeth, his stomach, and the account of him in the Bible. As mentioned, he would get scurvy if he had no vegetables in meat. The kidneys would be ruined by overwork. There would be protein poisoning and, in general hell to pay. ”
By the time Dr. Stefansson was publishing his memoirs, however, he and another arctic explorer, named Andersen, agreed to eat an all-meat diet for an entire year under the supervision of doctors of New York City's Belleview Hospital (no, not in its famous psychiatric department, in the medical ward). The findings of the experiment published in the Journal of Biological Chemistry. It is only fair to note that the costs of the study were subsidized by a grant from the American meat packers association.
Stefansson insisted on being fed a diet of lean meat without fat to demonstrate the problems he encountered in the Arctic. While on this protein-only diet, he began to experience nausea and vomiting after just two days. When Stefansson and Andersen went back on a meat and fat diet, however, they experienced no particular problems. In fact, they appeared to be in “the best health of their lives. ”
You and I, however, are not Arctic explorers. We may not be in the best health of our lives. For us, it might be a good idea to minimize our total meat consumption, and even to eat a little fat with the meat. But how much meat is too much? To get to the “danger zone” for human protein metabolism, 230 grams of protein per day, we would need to consume:
• 1100 grams (2-1/2 pounds) of lean ham.
• 1120 grams (2-1/2 pounds) boneless chicken.
• 1200 grams (2-3/4 pounds) of lean chuck roast.
• 8 kilos (18 pounds) of silken tofu (whether it's a good idea to eat tofu is another issue).
• 10-1/2 kilos (over 20 pounds, over 4 gallons) of chopped spinach.
Advocates of vegan diets insist that it is impossible to consume enough plant foods to build up toxic levels of protein. They are absolutely right. People who eat hunks of meat several times a day ignore the very real possibility of consuming too much protein, especially if the protein is consumed without fat (that is, the meat is strictly muscle meat, without any organ meats, marrow, or marbling). But most of us really are safe from either extreme as long as we avoid advice from diet purists.