Episode 112 Transcript – Are High Protein Diets Bad for the Kidneys?

Leah:

Hello and welcome to The Ideal Nutrition Podcast. I’m Leah Higl and I’m here with my co-host Aidan Muir, and today we will be exploring the question, are high protein diets bad for your kidneys? You may have come across the statement, “High protein diets stress the kidney.” The theory often is that having too much protein can cause waste buildup in your blood, and your kidneys may not be able to remove all this extra waste product, therefore, creating too much stress on those organs and damaging them. This is kind of a silly argument when we think about it, because when we think about exercise, that stresses the heart. But it doesn’t necessarily mean that exercise itself is bad for you. So instead of looking at it like that, we’re just going to go a little bit deeper and explain what the outcomes are of high protein diets, and why this isn’t the case.

Aidan:

So we’re going to start with the easy one, which is the evidence on people with healthy kidneys. So based on that above, that example you kind of talked about being like stress, et cetera, does this lead to downsides? Clearly, if protein was bad for kidneys, we should see that if you get a bunch of people with healthy kidneys, you give them a high protein intake, you should see a decline in their kidney function over time. Research on this topic is mixed if you look at individual studies, but when you look at it as a whole, it is incredibly largely in favor of no issues of high protein intake if you have healthy kidneys. That is the clear consensus of the evidence-based community, and often what we find.

I’m going to try and look at this from a balanced perspective and be like… I’m going to look at both sides of the coin. So there is… I’m going to use a negative example to start off with. There’s a 2020 review titled The Effects of High Protein Diets from Kidney Health and Longevity. And they found, using their words, “High dietary protein intake can cause intraglomerular hypertension, which may result in kidney hyperfiltration, glomerular injury and pressure urea.” They also reported that quality of protein might matter, with plant-based protein being less frequently linked with kidney function decline than animal protein in observational studies. The negative example did rely a fair bit on observational data, and acknowledged that in the conclusion. Once again, we’ve spoken heaps about observational data versus randomized control trials and everything like that. It’s hard to draw pretty strong conclusions from observational data.

Going at it from a different angle, a positive example, which I believe is far more reflective of the research, the 2018 systematic review looking at 28 studies found that there was no change in kidney function over time based on whether people had low, moderate or high protein intake, pretty clear sign that if there is any impact at all, it can’t be large at most. Then I just want to chuck in there, rather than just being like, “Hey, it’s fine. No issues,” I wanted to chuck in an interesting individual study. Jose Antonio has done a lot of crazy high protein studies. One of the ones he’s most famous for is he did one that I believe is 4.4 grams per kilogram of body weight protein per day. I’ve mentioned on the podcast before, but if this is your first time hearing it, just to choose a simple number, if somebody was a 100 kilos, that’s 440 grams of protein. It is absurdly high.

And I see some people citing that being like, “He did this, and kidney function was fine.” And I’ve read the study, and they didn’t measure kidney function in that. They just didn’t notice any issues. They weren’t actually measuring kidney function. But an interesting individual study I wanted to mention was one of his other studies, where they did measure kidney function. So they got 14 lifters to have one year of consuming 2.5 to 3.2 grams per kilogram of body weight protein, and they found no harmful effects on kidney function.

One year is a long time to do a kind of controlled study like that, but the numbers… That protein intake of 2.5 to 3.2 grams per kilogram is quite high. That is quite high. And my kind of not overly hot take is that I think that if you care about lifting, you should consume enough protein to maximize muscle growth, and probably just not go crazy high above that. So that range would be like 1.6 to 2.2 grams per kilogram body weight protein unless you’re exceptionally lean. But these numbers are significantly higher than that, and we’re still very safe. They couldn’t find any decline of kidney function.

Leah:

Yeah, awesome. And from the perspective of looking at how we measure kidney function, and why there is some nuance even around that in regards to protein, and resistance training, and taking creatine, so creatinine levels is something you get tested through a blood test and it is 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 simply taking creatine, having a high protein diet, and by doing a lot of training where there is a lot of protein breakdown.

So creatinine itself is a waste product, and by taking creatine, having a high protein diet where we’re breaking down that protein, and we’re training like there is going to be excess of this waste product, so we often see in athletes and people that are doing these things that their creatinine levels actually are elevated, but that in isolation is definitely not usually a definitive sign that there is an issue with kidney function. So something else that we can look at is something called cystatin, which is a better marker in this case, because when we have kidneys that are working just fine, but our creatinine levels are raised due to the previous things that we discussed, creatine, high protein, training, et cetera, the cystatin levels will actually be normal. So it’s just another way of looking at GFR and kidney function, and it’s more reflective of that in this case.

Aidan:

Yeah, and that’s super useful, because we work with a lot of athletes who are just sending it in training. If they get a blood test at pretty much any random interval they’re going to see elevations in creatinine, which is going to skew kidney function markers based on that. And a way around that is to have a week off training, and it can take a full week or more in some cases, stop taking creatine for up to 30 days to return to baseline levels, lower your protein, and it’s just less appealing than just measuring cystatin C.

Leah:

And just check that, see if there’s a bigger issue at play. But typically, there’s not. In a lot of my athletes, their blood tests will really often come back with high or elevated creatinine levels.

Aidan:

Yeah. And now we’re going to talk about a really nuanced topic, and this is, what about people with poorly functioning kidneys? And this topic is probably a little bit more important than you would think, because once again, going back to the evidence-based community, I see so many people talking about this concept of when you have healthy kidneys, it’s completely fine.

Once people are over the age of 60, almost everybody has chronic kidney disease, at least stage three. Their EGFR typically has dropped below 60 at that stage. Most doctors don’t… I don’t say this in a negative way, they just often won’t really talk much about it, because everybody over a certain age pretty much has that. It’s just a decline that naturally occurs as we age. And it’s like, well, is that healthy kidneys anymore? Is this protein thing we’re talking about still relevant? So I think we need to spend a moment talking about this topic.

And this will also be relevant to anybody who does have kidney issues as well. So what about people with poorly functioning kidneys? So there’s clinical practice guidelines from 2020 that really cover the nutrition on this well, and I’ve used historically some practice guidelines around this with certain clients. The current guidelines, or the 2020 ones, encourage reducing protein intake down to 0.6 grams per kilogram for people who have stage three to five chronic kidney disease, and don’t have any other health concerns such as diabetes. So that’s below an EGFR of 60 on a blood test.

So once again, it is quite relevant to a lot of people. There was a previous one, which I preferred a little bit more, which was in an older guidelines, I assume around 2016 or something like that, where they said… Maybe 2015. But they said one gram per kilogram of ideal body weight, which I don’t really like the ideal body weight measure, but it basically would mean if somebody had way more muscle mass, then at least it would give them slightly more protein, because 0.6 grams per kilogram for somebody who is 60 kilos versus somebody who’s 120 kilos-

Leah:

Very different.

Aidan:

It’s very different, yeah. If diabetes is present, then the clinical guidelines recommend 0.8 grams per kilogram and it is individualized forever for other cases. As I said, stage three is below 60, stage four is below 30. The logic here is that if the kidneys are functioning poorly, their ability to clear these waste products is reduced. And if these waste products build up, they can impair kidney function further, which could lead to a larger rate of decline.

This is an incredibly hard area for us to interpret research in, but the people who have written these guidelines have also had research supporting that showing a delay in the rate of decline when people go to lower protein intakes. And that’s the thing you mentioned at the start earlier where you said, “Let’s focus on outcomes, not just the mechanisms.” Because they could say that mechanism all they like, but if we don’t see a decrease in decline and everything like that, then how much does it really matter?

But the other thing that makes this nuance is it’s still not that clear cut, even though we see some of that stuff. There is a great example of this, there was a 2022 study from Korea with nearly 4,000 participants, where they got people with stage three to five chronic kidney disease, and they didn’t find any association between protein intake and mortality. So people who were just going about their lives consuming high protein intake and everything like that, were not dying earlier.

Obviously, that mortality measurement isn’t a perfect tool. Just stating the obvious. But the reason I still put that out there is because it shows not a clear cut situation, where it’s like higher protein intake means this will happen quicker and this will… It’s clearly a nuanced area. And another thing, just stating another kind of obvious point, is that if the lower protein intake thing is relevant, it probably becomes way more relevant in stage four and five than it does in stage three, because you can put two and two together… I think you’ll probably talk about this a bit later, but two and two together being if I’ve just said that everybody over the age of 60 pretty much has stage three chronic kidney disease, shouldn’t that mean that lower protein intakes would be better for people over the age of 60 for overall health, longevity, et cetera, et cetera.

Leah:

Which is not what we see. And I think that leads perfectly into our last section of this podcast, and that’s really talking about the downsides of going too low protein. So particularly looking at older populations, but just in general, going too low in protein can contribute to malnutrition and an increased rate of just general decline. So like you said, we don’t want people just over the age of 60, because they’ve got this slightly decreased kidney function, we don’t want to go, “Okay, just don’t eat much protein.” Because we know in terms of outcomes, mortality and just general rates of decline, that’s all going to be worse if the protein intake is really low. If anything, we need our elderly populations to be eating more protein than what they’re currently doing.

So looking at people with diabetes, there is a recommendation of a slightly higher protein intake, because we know that if people have high blood glucose levels, and their insulin resistance isn’t well managed, that can speed up the rate of kidney decline. So going slightly lower carb and higher protein is kind of the general recommendation here, where if high protein intakes were one of, I guess, the main causes of kidney decline, or if it was a really big deal, we wouldn’t have that recommendation. So even in that regard, it doesn’t make a lot of sense.

Aidan:

So as a bit of a clear cut type of summary, with people who have healthy kidneys, there’s clearly no issue with protein intake. That’s pretty clear cut. As kidney function declines, it just becomes nuanced. There is a bit of evidence that kidney decline could occur a little bit quicker with quite a high protein intake. These guidelines, they don’t come from nowhere. There’s some very smart people who’ve written them, they’ve interpreted the research, put it all together, and everything like that. But as I’ve said, I think it matters far more in the later stages than in the earlier stages, because just going back to that concept of over the age of 60, we see so many benefits of people increasing their approach in intake. With other factors as well, with earlier stages of chronic kidney disease, I recall reading those 2015, 2016 guidelines, and there was no nutrition recommendations until people hit that kind of stage three chronic kidney disease.

And in that stage, from those previous guidelines, I recall that protein intake, that was the first time protein intake had any introduction being like, maybe we should manage this stuff when we hit stage three. But when you hit stage four, stage five, then they’re looking at, let’s limit potassium intake, let’s limit sodium intake, because the kidneys have declined so far that even those things are going to play a bit of a role in terms of how much excess waste there is, et cetera. So once again, we see heaps of benefits of people over the age of 60 increasing their protein intake, and if this was dramatically speeding up the rate of kidney decline, I don’t think we’d be seeing those benefits.

Leah:

Excellent. This has been episode 112 of The Ideal Nutrition Podcast. A lot of people have left reviews lately, but we’d always love more positive reviews. So if you could do that, that would be amazing. But otherwise, thanks for tuning in.