Sunday, August 8, 2010

Here we go again: alleged kidney toxicity of high protein diets by Jerry Brainum

One of the enduring critiques about high protein diets is that they impose excess stress on the kidneys.I've been hearing this ever since I got into bodybuilding, over 40 years ago. The one thought that immediately comes to mind is since consuming a high protein intake is a common bodybuilding practice, shouldn't some bodybuilders who've followed long-term high protein (HP) diets all suffer from kidney disease? One problem with this is that in many cases, kidney disease isn't readily apparent, unless you undergo specific kidney function tests. Another thing to consider is that kidney function appears to decline with age in many people, with some studies showing that the average person over age 60 walks around with about 40% of kidney function. But even this significant age-related decline isn't enough to produce any overt symptoms in such people. Many people lose a kidney to disease, and live comfortably with only one working kidney.Others contribute one of their kidneys for transplant purposes, and suffer no apparent problems. It is known that when a kidney is removed, the remaining kidney has the ability to compensate for the lost kidney. Still, critics of chronic high protein diets insist that reducing protein intake as you age will likely help preserve kidney function, with the implication being that eating a high protein diet will eventually result in a severe loss of kidney function, which is a long-term process.
      Most of the "proof" that high protein diets are detrimental to kidney function are derived from studies involving those with pre-existing kidney disease, or from animal studies. And even the animal studies are hardly definitive. When animals are fed high protein diets, the workload of the kidneys increase. This is apparent by an increase in the filtering rate of the kidneys. The primary job of the kidneys is to filter the blood, and protein metabolic byproducts, such as urea, must be excreted by the kidneys. When this happens, the kidneys step up the filtering rate. Since the kidneys are now working harder, the idea is that this increased workload stresses the kidneys, resulting in eventual disease. This notion assumes that normally functioning kidneys aren't up to the task, which simply isn't true. Indeed, a 2004 study in which rats were provided with 50% protein diets showed no kidney strain or defects in the rodents. Another study of rats that featured a 60% protein diet also showed no ill effects in their kidneys. Of course, these were short-term studies, and most types of kidney disease are the result of long-term problems related to kidney function.
     The latest animal study that examined the relationship of protein intake to kidney function involved pigs. Pigs were chosen for this study because they have kidney structure and function similar to that of humans. The pigs received either a high protein (35% of total energy intake) or low protein (15% of energy intake) diet that both contained the same number of total daily calories. They consumed these diets for 4 to 8 months. The higher protein diet contained additional amounts of egg and dairy proteins. After 8 months, the pigs on the high protein diet showed enlarged kidneys at the 4 and 8-month marks. Renal and glomerular volumes (internal structure) were 60-70% higher in the HP pigs at the end of the study.The enlarged kidneys in the HP pigs also showed 55% more fibrosis (scar tissue) and 30% more glomerulosclerosis (scarring of the kidney filtering units) compared to the LP pigs.
      Studies of athletes, including bodybuilders, show that consuming a high protein diet doesn't appear to impose any severe stress on the kidneys that the organs cannot handle. As noted, most of the evidence suggesting that a high protein intake is bad for kidney function is derived from those with existing kidney disease. In those people, protein intake must be controlled to decrease the stress on kidneys that are not fully functional. But extrapolating this to those with normal kidney function isn't logical or scientifically sound reasoning. But there might be some truth to long-term effects of a high protein diet on kidney function.
      In a recent interview with a pathologist from Columbia University who specialized in kidney disorders, she suggested that it's actually body mass that really stresses kidney function. The larger you are, whether that mass results from fat or muscle, the more work your kidneys must perform in filtering the blood. She said that while a high protein diet itself isn't dangerous for kidney health, the combination of a large body mass and an excessive  long-term high protein diet of over 300 grams per day would likely increase the risk of scarring of the filtering units of the kidneys, which could eventually result in kidney failure. Recall that one established effect of consuming a high protein diet is increased production of urea, the nitrogen-based metabolic waste product of protein consumption. More protein means greater urea production, which must be dealt with by the kidneys. This involves a significant increase in kidney filtering of the blood, and it's not hard to understand how this, coupled with the increased filtering required for those with larger body mass (larger body mass equals more blood, which means more filtering in the kidneys) could raise the risk of future kidney problems.The obvious solution would be not to continue to ingest massive amounts of protein when you no longer need to such as ,as you age. Along with this, reducing your body mass, preferably bodyfat, would also ease the work of your kidneys.
      Other ways to preserve kidney function include preventing the onset of high blood pressure. While the kidneys require a certain level of blood pressure to properly function (too low a blood pressure can also cause kidney shutdown), too high a blood pressure damages the filtering units of the kidneys, leading to disease and loss of function. It's also vital to stay hydrated. Being dehydrated through not enough fluid intake concentrates toxins, including urea, in the kidneys, again leading to kidney damage. The practice of many bodybuilders of consuming a  high protein diet while restricting water intake is very harsh on the kidneys. One gram of urea nitrogen requires 40-60 milliliters of water for proper kidney excretion of the urea.

Yong J, et al. Long-term high intake of whole proteins results in renal damage in pigs.J Nutr2010: in press.

 ©,2015 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited

Have you been ripped off  by supplement makers whose products don’t work as advertised? Want to know the truth about them? Check out Jerry Brainum's book Natural Anabolics, available at


The Applied Ergogenics blog is a collection of articles written and published by Jerry Brainum over the past 20 years. These articles have appeared in Muscle and Fitness, Ironman, and other magazines. Many of the posts on the blog are original articles, having appeared here for the first time. For Jerry’s most recent articles, which are far more in depth than anything that appears on this blog site, please subscribe to his Applied Metabolics Newsletter, at This newsletter, which is more correctly referred to as a monthly e-book, since its average length is 35 to 40 pages, contains the latest findings about nutrition, exercise science, fat-loss, anti-aging, ergogenic aids, food supplements, and other topics. For 33 cents a day you get the benefit of Jerry’s 53 years of writing and intense study of all matters pertaining to fitness,health, bodybuilding, and disease prevention.


See Jerry's book at


Want more evidence-based information on exercise science, nutrition and food supplements, ergogenic aids, and anti-aging research? Check out Applied Metabolics Newsletter at