Diets rich in animal proteins increase risk of stone formation

The Physicians Committee for Responsible Medicine (PCRM) offers five simple steps that doctors can encourage their patients to follow to avoid suffering kidney stones: 1) Drink plenty of water or other fluids; 2) Follow a diet with generous amounts of vegetables, fruits and beans rich in potassium and low in sodium; 3) If calcium supplements are being prescribed, encourage patients to take them with meals, rather than between meals; 4) Avoid consuming animal products (beef, pork, chicken, eggs, fish), as their protein and sodium content increase the risk of stones; and 5) Hold the salt and sugar.

Although tropical climates do play a role in the formation of stones (presumably because perspiration leads to dehydration and a more concentrated urine), this problem is easily addressed if the individual keeps himself or herself hydrated. The more challenging risk factors have to do with what we eat: sugar, sodium and animal protein.

“Animal proteins cause calcium to be leached from the bones and excreted in the urine where it can form stones. Diets rich in animal proteins also increase uric acid excretion,” revealed PCRM’s nutrition and renal disease literature. It cited a controlled research study, published in the American Journal of Clinical Nutrition, where research subjects on a diet eliminating animal protein had less than half the calcium loss that they had on their baseline diet.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) cited, “meats and other animal protein—such as eggs and fish—contain purines, which break down into uric acid in the urine. Foods especially rich in purines include organ meats, such as liver.” NIDDK, which is part of the US medical research agency National Institutes of Health, said that “animal protein may also raise the risk of calcium stones by increasing the excretion of calcium and reducing the excretion of citrate into the urine. Citrate prevents kidney stones, but the acid in animal protein reduces the citrate in urine.”

Cut down on high-purine foods

US-based National Kidney Foundation, in its website, recommends that in order to prevent uric acid stones, individuals need to cut down on high-purine foods such as red meat, organ meats and shellfish, and follow a healthy diet that contains mostly vegetables and fruits, and whole grains. It would also be advisable to limit sugar-sweetened foods and drinks, especially those that contain high fructose corn syrup, and to limit alcohol consumption.

PCRM said: “The association between animal proteins and stones probably relates both to the amount of protein they contain and to their content of the sulfur-containing amino acids. In particular, the sulfur in cystine and methionine is converted to sulfate, which tends to acidify the blood. As a part of the process of neutralizing this acid, bone is dissolved, and bone calcium ends up in the urine. Meats and eggs contain two to five times more of these sulfur-containing amino acids than are found in grains and beans.”

“If increasing one’s risk of heart attack and cancer isn’t enough of an argument against high-protein diets (meat), the science is conclusive that they also cause kidney damage, kidney stones, and gout,” said Dr. Joel Fuhrman in his book “Eat To Live,” citing a study published in American Journal of Kidney Diseases, Journal of Internal Medicine and New England Journal of Medicine regarding the link between animal protein and diseases.

Sources: Remer T, Manz F. Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr. 1994;59:1356-1361; Lemann J. Composition of the diet and calcium kidney stones. N Engl J Med. 1993;328:880-882; Breslau NA, Brinkley L, Hill KD, Pak CYC. Relationship of animal protein-rich diet to kidney stone formation and calcium metabolism. J Clin Endocrinol. 1988;66:140-146.