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You may have noticed that we’ve become a nation obsessed with protein. To meet demand, everything from cookies to ice cream to boxed cereals is being beefed up with this macronutrient. Diet books, social media influencers and many health care professionals extol the virtues of a high-protein diet, including boosting metabolism and increasing satiety to help with weight loss efforts. The result is that Americans, both meat-eaters and plant-based, are largely consuming more protein than ever. And it can have a surprising effect on your kidneys and how they function.
Despite all the finer points of eating plenty of protein, the safety of habitually consuming high amounts of this macro has been questioned by some. Mainly, the fear is that going big on protein places a heavy burden on our kidneys, which may lead to renal damage. The kidneys are remarkable organs that filter waste compounds, excess nutrients and liquids out of the bloodstream, producing urine. Essentially, this is the true detox machinery of the body. And the metabolites of protein digestion including ammonia are among the compounds your kidneys are responsible for removing from the body.
So, it’s been proposed that consuming too much protein can overwork the kidneys and lead to increased strain and, eventually, a downturn in functioning. When the kidneys are damaged, waste products and fluid can build up the body. That can cause a range of symptoms including swelling in the ankles, nausea, weakness, and shortness of breath. If the damage gets worse, your kidneys may eventually stop working – which is life-threatening.
There is, however, a serious question as to whether there’s significant evidence to support this relationship in healthy individuals.
Is a high-protein diet safe for kidney health or not?
Good news protein fans: The majority of evidence suggests that, within reason, eating plenty of this macro won’t sucker punch your kidneys if they’re fully operational to start with.
A recent study in the American Journal of Clinical Nutrition assessed the association between daily protein intake and all-cause mortality among 27,604 American adults with varying degrees of kidney functioning, from highly impaired to fully operational. In those with impaired kidney functioning, a higher daily total protein intake (1.4 grams of protein per kilogram body weight or more each day) and a greater intake of proteins of higher biological value like meats was linked to a greater risk for premature death, whereas lower intake levels did not raise the risk for mortality. So, it appears this population can benefit from keeping their protein intake, especially from meats, at a more modest level so as not to overly tax their kidneys.
But here’s an interesting finding that applies to most people: The researchers discovered that, in individuals with normal kidney functioning, a low daily protein intake (less than 0.6 grams/kg/body weight) was associated with an increased risk for all-cause mortality. Higher intakes, meanwhile, lowered the chances for early death and had no negative impact on kidney functioning.
According to this study, instead of posing a danger to your kidneys and their natural detoxing capabilities, eating plenty of protein just might offer you a few benefits. And in healthy individuals, high protein intake may have no negative effect on the kidneys at all.
What if your kidneys aren’t in perfect health?
So, should you be cautious about your protein intake? While research suggests that those with normally-functioning kidneys should be just fine, it might not be the right approach for everyone. And a high-protein diet may potentially pose problems if you’re already suffering from issues in kidney function.
An investigation by researchers at Brigham and Women’s Hospital found that high-protein diets may be associated with declining kidney function in women who already have mildly reduced functioning of this organ as measured by the glomerular filtration rate (GFR) – an indication of how effectively our kidneys are filtering the blood to remove waste from the body. Women with impaired kidney function who consumed diets high in protein experienced the most significant decline in GFR.
On further analysis, the risk was greater with increased animal protein intake, indicating that the source of protein may be an important factor. Perhaps eating more plant-based proteins is gentler on the kidneys.
Importantly, researchers observed no association between high protein intake and decline in kidney function in women with normal functioning kidneys. And protein intake levels up to 3 grams per kilogram of body weight per day in men who were weight training was shown to not negatively impact kidney functioning.
The verdict on protein and kidney function
The take home message here is while protein restriction may be appropriate for the treatment of existing kidney disease, there’s a lack of evidence for a detrimental effect of high protein intakes on kidney function in healthy persons.
It’s worth noting that two major risk factors for kidney malfunctioning, to begin with, are high blood pressure (hypertension) and diabetes, both preventable and modifiable via a whole food, nutrient-dense diet. And, yes, one that brings protein to the table.