Some people (like maybe your mom or dad) are still worried about high protein diets blowing up your kidneys. Here's why they have nothing to worry about.
Almost all long-term weightlifters have gone through it. In an effort to be proactive about our health, we go to the doctor for a routine check-up or to delve a little deeper into what's going on physiologically and wham! The doc tells us that our kidneys are about to explode! And then, after the shocking news about our main filtration system, the doc lets us know that we may have had a heart attack! That's right, according to our doc, our high protein diets are about to kill us.
What in the wide, wide, world of amino acids is going on? After all, many of the well-educated and progressive sports nutritionists have been recommending higher protein diets for years. And since researchers have demonstrated repeatedly that higher protein diets help maintain a positive nitrogen status in weight trainers and athletes, high protein diets can't be all that bad, can they?
Well, doctors often think so. And let's not make the mistake of thinking that these doctors are "idiots" or lost in the dark ages of medical practice, probably blood letting to release the evil humors. It's not that simple. The truth of the matter is this: Weight training and higher protein diets do impact certain blood markers of health function, but it's my contention that in weight trainers, these markers aren't nearly as alarming as many general practitioners think.
Therefore, without further ado, I'd like to present a letter that all doctors and parents should read before taking an alarmist approach to a patient or teenage weightlifter's blood work. This letter is inspired by the countless emails I've received over the last few years from frantic patients who have been told that their health is being jeopardized by their high protein diets when it's most certainly not!
For the adults in the audience, you certainly have the power and discretion to make your own choices with respect to your health. Unfortunately, many of the emails I get are from teens whose parents control the protein purse strings. For them, it's not a matter of choice. Therefore, this letter is written in order that their parents are better able to understand the facts and make an informed decision.
Dear Mom and Dad,
I appreciate that you're taking an interest in your child's health. The fact that you're questioning the assumptions inherent in the weight lifting community is commendable and hopefully will instill in your child the ability to question established norms and to verify the veracity of the claims issued by the self-proclaimed bodybuilding "gurus." After all, blindly following–without proper discretion–what all the other "meatheads" are doing can definitely lead to problems.
In addition, I thank you for your objectivity in seeking out the truth (or the information that comes as close to the truth as we can currently get). It's difficult to remain objective in today's society where we are easily influenced by the moods and alarmist nature of our current media machine.
With respect to your concerns, no doubt brought on by the concern of a well-intentioned physician or by the results of clinical assessment (i.e. blood work), I'd like to address the relevant issues below.
Issue #1 – Many physicians believe that high protein diets cause kidney dysfunction
This is FALSE according to everything science now knows to be true. This presumption states that if you take a healthy person and put them on a high protein diet, the protein will somehow negatively influence the kidney, damaging it and causing renal disease. To this end, there is absolutely no data in healthy adults suggesting that a high protein intake causes the onset of renal (kidney) dysfunction. There aren't even any correlational studies showing this effect in healthy people.
Any studies that show a correlation between renal (kidney) dysfunction and protein intake are in those with some type of diagnosed, pre-existing renal (kidney) disease like diabetic nephropathy, glomerular lesions, etc. Even research into protein restriction for renal patients can be controversial. (Shils, Modern Nutr in Health & Dis, 1999).
Besides, you'll likely recognize a serious pre-existing kidney condition; the signs and symptoms will clue you in long before you happen upon it with a routine blood test (especially if there's a noted family history of diabetes mellitus and hypertension).
Since an exhaustive search of the published literature will likely not yield a single study showing that the amount of protein in the diet causes, or is correlated with, the onset of renal dysfunction in otherwise healthy individuals, the fact that this notion prevails is puzzling to say the least!
But even if a doctor were to find an obscure reference that might suggest a relationship between a high-protein diet and kidney disease, there are numerous studies showing otherwise. Here are a few of them:
- Ann Intern Med 2003 Mar 18;138(6):460-7. The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Knight EL, Stampfer MJ, Hankinson SE, Spiegelman D, Curhan GC.
- Int J Sport Nutr Exerc Metab 2000 Mar;10(1):28-38. Do regular high protein diets have potential health risks on kidney function in athletes? Poortmans JR, Dellalieux O.
- Int J Obes Relat Metab Disord 1999 Nov;23(11):1170-7. Changes in renal function during weight loss induced by high vs low-protein low-fat diets in overweight subjects. Skov AR, Toubro S, Bulow J, Krabbe K, Parving HH, Astrup A.
- Eur J Clin Nutr 1996 Nov;50(11):734-40. Effect of chronic dietary protein intake on the renal function in healthy subjects. Brandle E, Sieberth HG, Hautmann RE.
- Am J Kidney Dis 2003 Mar;41(3):580-7. Association of dietary protein intake and microalbuminuria in healthy adults: Third National Health and Nutrition Examination Survey. "Dietary protein intake was not associated with microalbuminuria in normotensive or nondiabetic persons."
Issue #2 – Many physicians believe that because high protein diets can worsen the condition of those who already suffer from kidney dysfunction, it only stands to reason that this should be true in healthy people.
This is also FALSE! Much of the speculation about kidney dysfunction associated with high protein diets comes from early nutritional studies in renal patients (patients who already have kidney disease).
In these individuals, when high protein diets are given as part of total parenteral nutrition–or tube feedings–these diets exacerbated their renal (kidney) problems. From these data, some physicians and nutritionists began to speculate (sometimes erroneously) that increased protein in the diet could be harmful to even those with healthy kidneys.
While there are hundreds of studies showing that high protein diets are bad for kidney patients, I believe that a "leap" from clinical patients to healthy patients isn't warranted. It's this leap that has been the cause of the persistent but slowly dying (sorry for the word selection) idea that high protein diets could harm the kidneys.
Again, there's no evidence whatsoever that high protein diets will harm the kidneys of a healthy weightlifter. This is about as ridiculous as someone suggesting that because eating certain types of fiber can worsen the GI symptoms of someone with irritable bowel syndrome, fiber must cause irritable bowl syndrome in otherwise healthy people.
Issue #3 – Kidneys DO change to adapt to high protein diets.
Some studies in healthy individuals do show an alteration of kidney function with very high protein diets. However, it's important to note that these changes are not reported as negative or "adverse." Instead, they seem to be structural adaptations to increased filtration (something the kidneys are doing all the time anyway).
If the kidney didn't respond this way, most clinicians would think something was wrong. Just like in weight training, tissues adapt to the demands put on them. Therefore, just because the kidneys have to "work" harder, doesn't mean that this is a negative thing. After all, what happens when muscles work harder? Well, they adapt to the demands and become bigger, stronger, or more efficient. Therefore, the adaptation that kidneys undergo is reasonable and appropriate. But don't take my word for it, check out this study:
- Eur J Clin Nutr 1996 Nov;50(11):734-40. Effect of chronic dietary protein intake on the renal function in healthy subjects.
Brandle E, Sieberth HG, Hautmann RE.
Issue #4 – What about the increased creatinine and BUN indicated by the blood test?
For starters, how about a quick discussion of the two markers?
Creatinine is commonly known as a waste product of muscle or protein metabolism. To this end, its level is a reflection of the body's muscle mass or the amount of protein in the diet. Low levels are sometimes seen in kidney damage, protein starvation, liver disease, or pregnancy. Elevated levels are sometimes seen in kidney disease due to the fact that a damaged kidney will not remove creatinine from the body as it should. Also, elevated levels are seen with the use of some drugs that could impair kidney filtration. Finally, elevated levels could also be seen with muscle degeneration, a high protein diet, or creatine supplementation.
With respect to creatinine measurements, it's important to note that the amount of creatinine in the blood is regulated by the amount being produced (from protein degradation–muscle or dietary) vs. the amount that's being removed (by the kidney). Therefore, although creatinine in the blood COULD be a marker of a damaged kidney's inability to filter creatinine out of the body at a normal rate, it COULD ALSO be a marker of rapid protein degradation (via muscle damage from weight training or from a high protein intake).
Think of the blood as a sink. If you turn on the faucet at a low rate, the amount of water going into the sink and the amount leaving the sink should balance each other out, leading to a predictable amount of water in the sink at any moment. However, if you partially plug the drain, you'll get more water accumulating in the sink at the same faucet flow rate. This is similar to kidney dysfunction (thinking of the water as creatinine). However, alternatively, if the drain remains unplugged but you crank up the faucet flow rate, you'll get more water in the sink due to the higher flow. This is similar to a high protein diet.
Since weightlifters are continually breaking down muscle protein (this is a good thing), even in the absence of a high protein diet, blood creatinine concentrations tend to be elevated. Furthermore, add in a higher protein diet and creatinine concentrations in the blood will rise. Finally, since creatinine is also a breakdown product of creatine, if a weightlifter is taking creatine supplements (which most do), blood creatinine concentrations will also be high. What all of this means is that the faucet is turned up in weightlifters, not that the drain is plugged.
To address the other relevant measure, the nitrogen component of urea, blood urea nitrogen (BUN), is the end product of protein metabolism and its concentration is also influenced by the rate of excretion (as is creatinine). Excessive protein intake, kidney damage, certain drugs, low fluid intake, intestinal bleeding, exercise, or heart failure can cause increases in BUN. Decreased levels may be due to a poor diet, malabsorption, liver damage, or low nitrogen intake. Excess BUN is even more closely correlated with protein intake than is creatinine. The same argument above applies here.
So, as you can see, since both creatinine and BUN are correlated with both high protein metabolism AND kidney function, I'm not suggesting that it's unreasonable that doctors are worried about the kidneys of your son or daughter. But it's important for you and your doctor to realize that the increases in BUN and creatinine seen in healthy weightlifters who eat higher protein diets aren't necessarily a function of kidney health but are much more closely correlated with their diet and training.
Issue #5 – Since BUN and creatinines are non-specific measures, what should we have tested, just to be on the safe side?
According to physician and sports nutrition expert Dr. Eric Serrano, two additional measures are important to tease out the differences between the effects of training and nutrition and the effects of kidney dysfunction. The first is the BUN to creatinine ratio. Dr. Serrano suggests that values up to the low 30's are okay but anything higher might be indicative of problems. The second is a urinary protein test. This test is a better measure of kidney function than most others.
Considering that most comprehensive kidney function tests include the following measures (A/G Ratio, Albumin, BUN, Calcium, Cholesterol, Creatinine, Globulin, LDH, Phosphorous, Protein - Total, Uric Acid) as well as urinary analysis, it seems irresponsible to make suggestions about protein intake after a simple blood chemistry analysis measuring BUN and creatinine.
Issue #6 – What about the increased levels of Creatine Kinase (CK)?
While this misdiagnosis isn't as common as the aforementioned ones, many doctors erroneously speculate that elevations in a muscle damage marker, CK, is indicative of a recent myocardial infarction (heart attack)! How could this be?
Creatine Kinase is a cytosolic enzyme (it floats around in the fluid portion of cells) involved in muscle metabolism. Since creatine kinase is present in all muscle tissues (including skeletal muscle and cardiac muscle), the excessive appearance of creatine kinase in the blood is indicative of some type of muscle damage (again, either skeletal or cardiac). Countless studies have shown large rises in blood concentrations of creatine kinase with heart muscle damage (via heart attack) and even large rises in creatine kinase with normal, training-induced muscle damage (this damage is critical to the growth and adaptation process).
Interestingly, a high protein diet has been repeatedly demonstrated to increase resting creatine kinase and post-exercise creatine kinase concentrations without any additional damage (in a number of different species, including humans).
Furthermore, while the standard clinical creatine kinase assay doesn't distinguish between skeletal muscle and cardiac muscle creatine kinase isoforms, there are muscle specific tests that can be done. Therefore, if a doc is worried about elevated creatine kinase, he or she should order a creatine kinase isoform test. This will determine whether the creatine kinase was released from skeletal or cardiac muscle.
In the end, if a doc is sitting in front of a high protein eatin' weight trainer with lots of muscle mass (skeletal muscle creatine kinase release, as you might imagine, is closely related to total muscle mass) and sees an elevated creatine kinase score, the last thing on his or her mind should be "heart attack." Here's a reference to check out:
- Med Sci Sports Exerc. 1999 Mar;31(3):414-20. Effects of dietary protein on enzyme activity following exercise-induced muscle injury. Hayward R, Ferrington DA, Kochanowski LA, Miller LM, Jaworsky GM, Schneider CM
I'll end my arugment here. I hope that I've been able to assist in your search for the facts about protein intake and renal function. However, I feel that I'd be remiss if I were to leave out the other side of the coin – an article that I've written that highlights the myriad of benefits associated with high protein intakes.
John M Berardi, BSc, CSCS, PhD Candidate