How High-Protein Diets Damage the Kidneys

Many people are currently using high-protein diets, such as the Atkins diet, to lose weight quickly. Although some doctors and nutritionists believe these diets are safe for healthy adults, others warn of risks to the kidneys. Whether the amount of damage is negligible, or substantial enough to warrant caution, is still the subject of some debate. If you have kidney or liver damage, a high-protein diet can be harmful. Consult your doctor before embarking on this diet.

Features of High-Protein Diets

To follow a high-protein diet, eliminate or drastically reduce your intake of fruit, fruit juices, bread, rice, pasta, and grain products, and focus on eating meats, cheeses, eggs, and non-starchy vegetables.The philosophy behind this regimen is that drastically restricting carbohydrates, such as starches and sugars, will cause the body to turn to other fuels for energy -- either from fats and protein, or from stored body fat. When dietary fat or stored fat is used for energy, the process produces ketones, and people on high-protein diets use these ketones in their urine as a sort of yardstick for measuring progress.

There have not been any long-term studies to demonstrate the safety and effectiveness of this method, and it remains controversial. Some doctors give high-protein diets their approval, saying they can result in not only weight loss but lowered fat -- or lipid level -- in the bloodstream. Others say that any weight loss occurs because people on a high-protein diet automatically consume fewer calories, that the food selections are too limited and fatty, and that high-protein diets are no more effective than conventional diets such as those offered by Weight Watchers.

Kidney Damage

According to Katherine Zeratsky, a registered and licensed dietitian and nutritionist at the Mayo Clinic, damage to kidneys from a high-protein diet results because of the way protein is metabolized. Protein in the diet is normally broken down into amino acids, and used to make enzymes. Any "extra" amino acids are stripped of nitrogen; the non-nitrogen parts go for energy or are converted to fat; the nitrogen itself -- now a waste product of the metabolization process -- ends up not only in the liver but in the kidneys, where it can cause injury (see Reference 1).

In addition, high-protein diets increase the risk of kidney stones. In an attempt to flush the system of uric acid and urea -- toxic by-products of protein breakdown -- the kidneys may steal calcium from the bones; these calcium deposits sometimes form into kidney stones.

Zaratsky also points out that although high-protein diets are generally well-tolerated by healthy adults, they include still more health drawbacks. These diets, by their restrictive nature, limit other healthy foods vital to health and proper nutrition, including whole grains, fruits, and vegetables. In addition, many high-protein foods -- meat, milk, cheese, and eggs -- are high in fat and cholesterol. If you do try this diet, keep in mind that fish, beans, lentils and low-fat dairy products are better choices for fulfilling protein needs.

Precautions

If you have any kidney problems, no matter how slight, you should not embark on a high-protein diet, unless your physician specifically tells you to. According to Dr. Eric Knight, M.D., MPH,, who conducted a nurses' health study at Brigham and Women's Hospital in Boston, women with mild kidney problems who ate a high-protein diet had a faster loss of kidney function than those who did not (see Reference 2). If you do try the diet, have regular kidney function tests and be monitored by a physician.