Last week we looked at two articles that claimed an association between people in the highest protein intake group and worsening measurements for kidney function – a possible marker for kidney disease. We found that the intake of calories and protein in the comparator groups were so absurdly different, that they were not credible.
This week we ask the proper research question – do high protein diets cause kidney disease?
The best way to examine any research question is to search the academic literature for all evidence. Presenting the latest couple of studies, especially when epidemiological, is just cherry picking.
I use PubMed to search academic literature. I look for key terms in the title and/or abstract, on the basis that – if a paper doesn’t mention the terms of interest in either the title or the abstract, the paper is unlikely to be primarily about the search terms. I also always tick “humans” on the left hand side, as I’m interested in people, not Mickey Mouse or Roland Rat!
Searching for “Kidney disease” AND “high protein diet” OR “high protein diets”, in humans, produced 21 results. Having done several systematic reviews for my PhD, I’m familiar with the fact that a search with specific terms still elicits many papers that are not relevant to the research question. This search was no different. Over one third (8) of the 21 papers were about protein intakes/modification in existing chronic kidney disease (CKD), or progression thereof, and thus could be discarded for this review. A further six could be discarded following review of the abstract: two were about nutrients/supplements (vitamin A and creatine); one was an individual case study; one was about advanced glycation end products; one was specifically not about kidney disease; and one was about bodybuilders abusing steroids and growth hormones (as well as protein).
Among the remaining seven papers, there were no systematic reviews or meta-analyses. These would have provided the best evidence available. There were two clinical trials and five reviews.