Research & Education

Protein Mythbusting, Part 2: Does Protein Damage the Kidneys?

“Not only are there zero case reports of kidney injury from high protein diets—the medical dogma of restricting protein in chronic kidney disease is almost purely mythical.” (Theodore Naiman, MD, a family physician well known in the low carb and ketogenic community)

“Increased dietary protein is thought to have impact on renal function. What needs to be recognized is that the thesis that dietary protein is causative for renal disease is not supported by evidence.” (Stuart Phillips, PhD, a prominent researcher on protein and athletics)

Somewhere along the way, the idea that dietary protein is harmful for the kidneys became lodged in the collective health psyche, and it refuses to disappear, even though there’s little to no research to back it up. We recently explored the role of protein in bone health, dispelling the widely believed, but false, notion that a high protein intake is harmful for bones. Let’s turn our attention to protein and the kidneys and see if the evidence stacks up in favor of protein restriction, or if this is another nutrition myth that could use a good busting.

It’s long been believed that humans should aim for a protein intake of approximately 0.8g per kilogram of body weight per day. Some authorities would even argue that this should be 0.8g per pound of lean body mass per day, which, for most people, would mean a substantially lower total protein intake. Despite its widespread parroting, many experts disagree with the 0.8g/kg/d axiom, pointing to many favorable outcomes with higher protein intakes, and some even say, “there is an urgent need to reassess recommendations for protein intake in adult humans.”

Jose Antonio, PhD, a researcher and associate professor of exercise and sport science, wrote, “Anyone who thinks the RDA for protein should be 0.8 g/kg/d has apparently missed the last 3 decades of scientific progress in nutrition.” Dr. Antonio has done extensive research into protein and the athletic community, with relatively long-term studies employing higher protein intakes (2.0g/kg/d and higher). If higher protein intakes were harmful for the kidneys, it’s likely the bodybuilding community would be rife with kidney problems, and that high-protein eating bodybuilders would be a dialysis clinic’s best customers. To the contrary, you don’t see lean, strong, well-muscled people lining up at these centers. The largest contributor to kidney dysfunction is chronically elevated blood glucose and insulin, stemming mostly from type 2 diabetes. Of all the factors that increase for chronic kidney disease, not included is a high protein intake! 

A systematic review of renal health in healthy subjects consuming protein at levels above the US RDA (0.8g/kg/d) determined that “increased protein intake had little or no effect on blood markers of kidney function,” and that, “at least in the short term, higher protein intake within the range of recommended intakes for protein is consistent with normal kidney function in healthy individuals.” Within the range of recommended intakes for protein means up to 35% of calories, since the Food and Nutrition Board of the Institute of Medicine of the U.S. National Academies of Sciences determined that the acceptable range of protein intake as a percentage of total calories for adults is 10-35%.

According to a report by the World Health Organization, Protein and Amino Acid Requirements in Human Nutrition: “the suggestion that the decline of glomerular filtration rate that occurs with advancing age in healthy subjects can be attenuated by reducing the protein in the diet appears to have no foundation.”

It’s true that once someone’s kidney function is already substantially compromised from the things that actually do harm the kidneys (like diabetes and hypertension), they might have a reason to limit protein intake. But just because damaged and poorly functioning kidneys may not be able to handle a “normal” protein load doesn’t mean it was protein that caused the damage. If someone breaks a leg in a skiing accident and they can’t walk for a few weeks, they can’t walk, but it wasn’t walking that caused the break. The leg was damaged by something else that then affected the ability to walk.

Dr. Phillips pulled no punches when he wrote that the idea that protein is harmful for the kidneys is “usually derived from circular logic of people’s experiences in renal wards where there’s little doubt that lower protein diets can help extend a persons’ health and life due to the lower urea and therefore less ‘work’ filtering such substances by the kidney. The incorrect circular logic that is then applied is that ‘therefore’ [sic] high protein diets cause renal disease. That’s poor logic, flawed reasoning, and just plain wrong.”

Even the part of this that’s still tempting to cling to—that protein restriction might be warranted in those with already advanced kidney disease—is less convincing when you look more closely at the evidence. In a study of patients with chronic renal failurea low protein diet (0.4 to 0.6 g/kg/d) delayed the progression rate of renal failure only in patients with primary glomerular disease, and only in males. Female patients did not benefit at all. Considering primary glomerular disease accounts for only about 7% of all kidney disease (with 44% attributed to diabetes and 29% to hypertension), this is an intervention that would benefit very few people. Protein restriction should not be dismissed for the few individuals whom it would help, but it should not be recommended across the board for all kidney patients, and certainly not for healthy people with no valid reason to limit protein intake.

A different study of patients with chronic renal failure showed that a diet of 0.6g/kg/d led to no significant difference in rate of fall of creatinine clearance compared to a diet that met the RDA of 0.8g/kg/d. It’s possible that an even greater reduction in protein intake might have resulted in a more favorable outcome, but 0.5g/kg/d or lower would likely not be sustainable and could conceivably lead to problems from protein malnutrition.

Even in studies where protein reduction is shown to be beneficial in those with kidney disease, the results typically aren’t all that spectacular. At best, restriction merely delays the decline in function, rather than halting or reversing it. This isn’t reason to dismiss protein reduction as a therapeutic strategy, but patients should be made aware of the cost/benefit ratio.

Considering the undeniable role of chronically elevated blood glucose and insulin in driving kidney damage (and the role of hyperinsulinemia as a primary cause of hypertension even in non-diabetics), reducing carbohydrate intake seems a more prudent recommendation than reducing protein for maintaining healthy kidney function over the long term. Again, just because damaged kidneys may not handle protein as well as healthy kidneys doesn’t mean it was protein that created the damage in the first place.  

By Amy Berger, MS, CNS