If there’s one thing popular opinion is good at, it’s scaring you off of doing healthy things. If it’s not mid-20th century doctors warning that lifting weights would lead to heart problems and low sex drive, or modern “experts” saying kids shouldn’t lift weights, or the fear of anyone squatting deep, or women being told that strength will make them bulky… the list goes on. Today we want to look at perhaps the most common aspect of dieting seen among athletes: the high protein diet.
Editor’s note: The content on BarBend is meant to be informative in nature, but it should not be taken as medical advice. The opinions and articles on this site are not intended for use as diagnosis, prevention, and/or treatment of health problems. If you are suffering or suspect you may be suffering from any illness or medical condition, please seek advice from a medical professional. It’s always a good idea to talk to your doctor before making any large changes to your diet or training protocol, and regular check-ups can be helpful in this regard.
“If it makes you look, feel, and perform great, there has to be something wrong with it. Isn’t it bad for your kidneys? Yeah. High protein diets are bad for your kidneys. All these idiots lifting weights and chugging protein shakes are destroying their bodies. Armed with this information, I can avoid diet and exercise and feel good about it.”
Let’s unpack this a little.
But What Is a High Protein Diet, Exactly?
If we’re going to start talking smack about high protein diets, we need to define what we mean, and people are generally bad at doing that. Sometimes it’s defined as percentage of total calories, sometimes it’s grams per pound of bodyweight, and the cutoffs are always arbitrary and vary by researcher, field, or consensus.
The RDI suggests 0.36 grams per pound of bodyweight, or 0.8 grams per kilogram. Anyone who’s been in the strength game for a while will be more familiar with another number: 1 gram of protein per pound of bodyweight, every day. Two hundred grams for a two-hundred-pound person.
We’re not trying to say that is the optimal amount of protein to consume — many get by just fine on much less — but that’s the number we hear thrown around the most.
[Can you absorb more than 30 grams of protein at once? Check out our article.]
Is a High Protein Diet Bad for the Kidneys?
This idea gained steam after some studies were published in the late 1980s and early 1990s that showed the more protein people consumed, the greater their glomerular filtration rate (GFR), a marker for waste filtration in the kidneys.(1) Scientists claimed that increased GFR meant the kidneys were experiencing undue stress.
But later studies showed that it wasn’t the case for folks with healthy kidneys.(2)(3)
There’s also research that specifically looked at athletes. A crossover study of resistance-trained males found that guys who ate 3 grams per kilogram of bodyweight (almost 1.5 grams per pound) had no harmful effects on kidney or liver function.(4) Another study of bodybuilders consuming upwards of 1.3 grams per pound bodyweight also had no problems with the way their kidneys cleared creatinine, urea, and albumin.(5)
So, problem solved, right?
[Learn more: 4 Science Based Protein Rules for Athletes.]
I Noticed You Said “Not For Healthy Kidneys”
Eating a high protein diet probably isn’t bad for you, but doing so with unhealthy kidneys probably is. Restricted protein diets are often recommended for people with kidney damage, as it may slow its progression.(6)
Or as biochemist and nutritionist Dr. Trevor Kashey puts it: running isn’t bad for you, but running with a broken leg is.
“But that doesn’t mean running will break your leg,” he adds. “Just because something may make a condition worse, doesn’t mean it caused it. High protein won’t cause kidney problems unless you have a kidney problem, in which cast it might make it worse.”
The bummer is that some kidney problems, like chronic kidney disease (CKD) are progressive and asymptomatic, so by the time you feel like something is wrong damage has been done. And your high protein consumption may have worsened it.
“Kidney problems rarely happen in isolation — patients are usually already overweight, diabetic, have high blood pressure, or other more readily noticeable health problems,” says Kashey. “It’s true that a very small percentage of people have genetic issues related to kidney function, so yearly physicals, even as a young person, are a good idea.”
There’s a lot more to the equation when it comes to protein: how much should you have, how often should you eat it, does the amino acid profile matter, and so on. When it comes to whether or not that recommendation for 1 gram per pound of bodyweight is bad for the kidneys, the answer is no, but not an emphatic no.
It’s irresponsible to say that there’s no way it could ever be detrimental to kidney function, but if you’re healthy — and you’ve been getting regular check-ups to prove it — high protein likely shouldn’t be an issue.
Featured image via @proportionalplate on Instagram.
- von Herrath D, et al. Glomerular filtration rate in response to an acute protein load. Blood Purif. 1988;6(4):264-8.
- Knight EL, et al. The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Intern Med. 2003 Mar 18;138(6):460-7.
- Beasley JM, et al. Higher biomarker-calibrated protein intake is not associated with impaired renal function in postmenopausal women. J Nutr. 2011 Aug;141(8):1502-7.
- Antonio J, et al. A High Protein Diet Has No Harmful Effects: A One-Year Crossover Study in Resistance-Trained Males. J Nutr Metab. 2016;2016:9104792.
- Poortmans JR, et al. Do regular high protein diets have potential health risks on kidney function in athletes? Int J Sport Nutr Exerc Metab. 2000 Mar;10(1):28-38.
- Levey AS, et al. Effects of dietary protein restriction on the progression of advanced renal disease in the Modification of Diet in Renal Disease Study. Am J Kidney Dis. 1996 May;27(5):652-63.