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High-protein diets do not affect GFR in healthy individuals
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A high-protein diet likely does not adversely influence kidney function or glomerular filtration rate in healthy adults, according to recently published findings.
The results contradict the Brenner hypothesis, which proposed that regular consumption of excessive dietary protein has a negative impact on kidney function resulting from a sustained increase in glomerular pressure and renal hyperfiltration. Following this hypothesis, the assumption has been persistent in the decades following the 1982 study, even being applied to healthy individuals who do not have kidney disease.
“In somebody who's healthy, that's not necessarily the case,” Michaela Devries-Aboud, PhD, assistant professor of kinesiology at the University of Waterloo in Ontario, Canada and lead researcher of the recent study, told Nephrology News & Issues. “The premise is that in somebody with kidney disease, protein causes further damage and leads to poorer outcomes. The jump was then made to say that if protein does this in kidney disease, it must do it in healthy individuals as well; but there was no real evidential support for that.”
Many American and Canadian studies indicate that the general population consumes about 1.3 grams to 1.4 grams of protein per kilogram of body weight per day, according to Devries-Aboud, which is above the recommended dietary allowance. As most people are above the recommended daily allowance and the researchers receive many questions related to protein intake and kidney function, Devries-Aboud and her colleagues decided to tackle the issue and shine a light on the murky intersection of high protein and kidney function or GFR.
The researchers conducted a meta-analysis that included randomized control trials with a focus on the difference between high protein vs. lower protein groups. To differentiate from and improve upon a previous meta-analysis, they looked at the effect of consuming a higher protein intake on the change in kidney function rather than GFR following an intervention.
“Because there's such a variability in what's considered normal GFR and normal kidney function within the general population, just looking at the GFR following an intervention isn't actually telling us what's going on within each individual's body in response to that protein intervention,” Devries-Aboud said. “We wanted to do a comparison looking at whether or not there's a greater change induced by consuming a higher protein diet on GFR and then compare that to the results that were done when we only looked at the post-intervention GFR.”
“I do think our paper provides a clear and convincing story that people just need to stop saying that protein causes kidney disease or contributes to its progression,” Stuart Phillips, PhD, FCAHS, FACSM, FACN, an author of the study, told Nephrology News & Issues. “That’s reverse logic based on the Brenner thesis (note: thesis) and the treatment of people with renal disease, but there are a number of ‘rogue’ nephrologists who now question the wisdom of this approach. Prudent consumption of high-quality protein should be the mantra, not just eat less protein. That advice leads to rapid muscle loss and eventually reductions in physical function and worsening quality of life.” – by Joe Gramigna
Reference:
Devries M, et al. J Nutr. 2018; doi:10.1093/jn/nxy197.
Disclosures: Devries-Aboud reports no relevant financial disclosures. Phillips reports he has received grant funding, travel expenses and honoraria for speaking from the US National Dairy Council, The National Cattlemen’s Beef Association and Pepsico.
Perspective
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Becky Brosch, RDN, CSR, LD
In recent years, many have been seeking higher-protein diets as an option in their weight loss efforts. In addition, the typical protein intake in the western diet exceeds the 0.8 gm/kg DRI recommendation. These practices have brought concerns about the impact of a higher protein load on kidneys.
The recent meta-analysis by Devries-Aboud and others was conducted to determine the effect of high protein intake on kidney function in healthy adults. In summary, they determined that high protein intakes do not adversely influence kidney function on GFR in healthy adults. In my perspective, the key words are “high protein intake” and “healthy individuals.” The study relates that their findings are contrary to the Brenner hypothesis, which established that high protein intake can compromise kidney function due to the renal solute load. Most of the studies conducted by Brenner had subjects with impaired kidney function, thus the existing controversy is whether the hypothesis should be applied to healthy individuals.
So, what does the scientific research show?
Martin and colleagues reviewed the available evidence and concluded “while protein restriction may be appropriate for treatment of existing kidney disease, we find no significant evidence for a detrimental effect of high protein intakes on kidney function in healthy persons after centuries of a high protein Western diet.”
Pederson and colleagues performed a systematic literature review and concluded that “evidence is inconclusive regarding the harmful effects of a high protein intake on healthy individuals,” but also pointed out that “it cannot be entirely ruled out that a high protein intake may affect kidney function in the long term.”
What is the practical application of this information for a dietitian? What dietary intervention regarding high-protein diets should be applied for healthy individuals?
While it appears that high-protein diets are not harmful to healthy individuals, there are still unknowns about long-term effects. As we know, a dietitian’s role is to work with patients on establishing nutrition goals, providing education and coaching them to success. There is not a “one-size-fits-all answer.” Using our clinical expertise and consultation with the patient’s physician, we assess each patient utilizing subjective information on preferences, risk factors, comorbidities, labs and anthropometrics to determine individual needs and goals. Still open for further debate is: What is the impact of plant-based protein vs animal-based protein? Does one have less impact on the kidneys than another? What is the optimal protein intake for aging adults? The debate continues, but the role of the dietitians is consistent: Work with each patient on his or her individual needs to achieve lifestyle changes that are impactful for health and well-being.
References:
Brenner BM, et al. N Engl J Med. 1982;doi:10.1056/NEJM198209093071104.
Devries M, et al. J Nutr. 2018;doi:10.1093/jn/nxy197.
Martin W, et al. Nutr Metab (Lond). 2005;doi.10.1186/1743-7075-2-25.
Pedersen A, et al. Food Nutr Res. 2013;doi:10.3402/fnr.v57i0.21245.
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