Key Topics Covered
You may have come across the statement, “High protein diets stress the kidney”.
The theory is often that having too much protein can cause waste to build up in your blood, and your kidneys may be unable to remove all the extra waste. Therefore, creating too much stress on those organs.
However, when you think about other ‘stressors’ such as exercise, this may not be a viable explanation. Instead, it makes sense to focus on particular outcomes.
Evidence on Healthy Kidneys
- The research is mixed, however, it is mainly in favour of no issues being caused by a high protein intake if you have healthy kidneys.
- There is some research showing negative outcomes though.
- A 2020 review found “High dietary protein intake can cause intraglomerular hypertension, which may result in kidney hyperfiltration, glomerular injury, and proteinuria”.
- They also reported the quality of protein might matter, with plant-based protein being less frequently linked with kidney function decline than animal protein, in observational studies.
- That negative example did rely a fair bit on observational data though, and acknowledged that in the conclusion.
- A positive example that is more reflective of the research is a 2018 systematic review, including 28 studies that found there was no change in kidney function over time based on whether people had low, moderate, or high protein intake.
- That’s a pretty clear sign that if there is any impact, it cannot be large.
- Another study looking at 14 lifters who were consuming 2.5-3.2g/kg protein for one year showed no harmful effects on kidney function.
Nuance About Creatinine Levels From Protein, Lifting and Creatine
What are creatinine levels?
- Creatinine levels are used to estimate GFR which gives us an idea of how well the kidneys are functioning.
- GFR can be raised above the healthy reference range by taking creatine, having a high protein diet, and doing a lot of training where there is protein breakdown.
- However, the creatinine levels in isolation are not a definitive sign that there is any issue with kidney function.
- Cystatin C can be a better indicator. When kidneys are working well, cystatin levels are typically within a certain range. And these levels can be used as another way of estimating GFR.
Protein in Those With Poor Kidney Function
- 2020 clinical practice guidelines encourage reducing protein intake down to 0.6g/kg for people in stage 3-5 CKD, who don’t have other concerns such as diabetes.
- Stage 3 CKD is <60eGFR. Stage 4 is <30eGFR
- If diabetes is present it goes up to 0.8g/kg. It is individualized further for other cases.
- The logic here is that if the kidneys are functioning poorly, their ability to clear these waste products is reduced. And if they build up, it can impair kidney function further.
- They also had research supporting this, showing a delay in the rate of decline.
- This is still a very nuanced area though– A 2022 study from Korea with nearly 4,000 participants with stage 3-5 CKD didn’t find an association between protein intake and mortality.
- Obviously that “mortality” measurement isn’t the perfect tool here. But it still shows that it isn’t a definitive outcome.
- The lower protein intake likely becomes more relevant in stages 4 and 5 than in stage 3.
Downsides of Going Too Low
- Consuming too low protein can contribute to malnutrition and an increased rate of decline.
- High BGLs speed up the rate of kidney decline, which is likely part of why the guidelines for diabetes are a bit higher.
- A large percentage of people over the age of 60 fit the criteria for stage 3 CKD.
- We have a wealth of evidence about the benefits of protein for reducing sarcopenia.
- With people who have healthy kidneys, there is clearly no issue with high protein intake.
- As kidney function declines, this is where it becomes more nuanced.
- We also see benefits when those over 60 increase their protein intake.
- If high protein intakes were detrimental, we would expect to see negative outcomes.
Relevant Links / Resources
- 2020 Review of Protein and Kidney Function Decline
- 2018 Review Showing No Difference
- Study On Lifters
- 2022 Korean Study