Podcast Episode 77 Transcript – Are High Protein Diets Bad For Gut Health?

Aidan Muir:

Hello and welcome to the Ideal Nutrition Podcast. My name is Aidan Muir and I’m here with my co-host Leah Higl. And this is episode 77 where we will be talking about whether high protein diets are bad for gut health, which I don’t think it’s a super talked about topic. It’s not a massive topic. But every now and then I do see people saying that high protein diets are bad for gut health. I think hearing that as somebody who is in the fitness space and working with a lot of people who do follow higher protein diets, there’s two questions that instantly came to my mind the first time I heard anybody make reference. That is, are they bad for gut health? And if they are, is there anything we can do to offset that? Which will be mostly what we’re covering today.

Leah Higl:

First thing to get clear on is definitely the definition of what gut health means, because there’s two different avenues you can go down when we’re talking about definition for this. So what we will be talking about is the definition being really talking about the ratio and diversity of gut bacteria. So the overall diversity of the gut microbiome being an indicator of overall gut health. Although it’s not a super clear cut thing. We don’t really know what the gold standard gut microbiome should look like. So it’s one of those harder things to gauge, but what the, we’ll talk about some studies later on that they really look at the overall kind of diversity and amount of different kinds of bacteria in the gut to gauge that.

But something else in regards to gut health is people will talk about gut health in relation to gastrointestinal symptoms, maybe in regards to IBS and linking good gut health equals you don’t have any gut symptoms. I think there’s a bit of a disconnect here because we do know things that are really good for gut health like highly fermentable foods may cause gastrointestinal distress but are feeding good bacteria in the gut and actually contributing to good gut health. So those two things don’t always go hand in hand the way you think they would. So when we’re saying gut health, at least within this context, it’s more around the overall quality of the gut microbiome more than anything else.

Aidan Muir:

So taking it a step further from what is gut health to the next obvious question, if we get a definition of what gut health is, how do we measure it? How do we assess it? The simplest way based on that kind of definition of assessing it is looking at firstly measuring the bacteria that we have, measuring the abundance of “good” types of bacteria and also measuring bad pathogenic bacteria. Obviously that’s complex because it’s clearly not that simple just being these bacteria are good, these ones are bad. There’s way more nuance to that. But this is the most simple way that we can measure it, being like these bacteria are associated with good health outcomes, these ones are associated with bad health outcomes. That’s the simplest way even if it’s not the most nuanced way or most accurate way really. Measuring the diversity of bacteria. On average, it seems like having a wider diversity of bacteria is a good thing. So that’s one thing that can be measured.

And then obviously simply from the IBS standpoint is monitoring symptoms. If those are improving, that’s an easy way we can kind of assess that kind of stuff. Then in terms of how do we literally measure it, the most common way seems to be measuring bacteria in stool samples. That seems the most common one. That is flawed in a way in that it’s like how do we know the bacteria that ends up in the stools is representative of what is in the intestine? That it’s overly simplistic because it can actually miss a lot of really useful information but it’s the easiest way and it’s the most common way from memory. Even that American Gut Project, that’s one of the biggest studies that’s ever been done. From memory and it could be wrong, but I’m pretty sure they’re just sending stool samples for that.

Leah Higl:

That would make sense.

Aidan Muir:

That’s how they’ve come back to the conclusion of having a wider variety of plant-based foods is good. That’s overly simplistic but that’s the most popular way people have come to that conclusion. So that’s how we’d measure it.

Leah Higl:

Final thing to define before we jump into this is what even is a high protein diet and how do we define that generally? Is it the total amount? Is it percentage of total calories? And we would say that anything that is 25% or more of your calories coming from protein would be above that acceptable macronutrient distribution range. So that could be counted as a high protein diet. Or another way to look at it is potentially maybe more than 1.4 grams per kilo of body weight per day being considered a high protein diet. So that’s two ways you can go about looking at that, but we just wanted to jump in and define that as well first.

Aidan Muir:

Yeah, I think definitions are important because, I don’t know, using carbohydrates as an example. In research, a low carb diet is defined as less than 40% of total calories, whereas in the real world nobody’s calling somebody having 35% total calories come from carbs as a low carb diet. That’s the acceptable macronutrient distribution ratio kind of thing. This is where it gets murky because it’s like what if somebody is in a massive calorie deficit and they’re having 30% of calories come from protein, but there’s a low total amount. That’s why I like a combination of both of those things. Even though it makes it less clear, it’s useful for this discussion.

And what changes are reportedly seen on a high protein diet? So the two most obvious ones that people often point to when they are saying that a high protein diet does lead to these issues is there is a decrease in bacteria that produce short chain fatty acids such as bifidobacteria. These are typically good bacteria, these short chain fatty acids are typically good things so we don’t want them decreasing. And there is often a reduction in diversity of bacteria in the microbiome seen from higher protein diets, which is what we’re looking at.

Leah Higl:

So let’s get into the meat of it and that’s really looking at two different studies. So I have to say research on this topic, there’s not a ton of research to-

Aidan Muir:

There’s a lot less than I thought there’d be when I was looking.

Leah Higl:

There’s not a ton but there’s two key papers that we’re at least going to look through today. So buckle in because I’m going to take a moment to go through these. But the first one is the Korean study. So it was a study that was published in 2019 and they compared fecal microbiome so stool samples characteristics amongst three different groups. So that was bodybuilders, distance runners, and a control group of just sedentary men. Then they assessed the relationship between the gut microbiome and what they got from the stool samples and body composition athlete type and dietary intake. What we are particularly interested in is going to be that link between dietary intake and the changes in the gut microbiome. So amongst bodybuilders, there was a general reduction in bacteria that produced those short chain fatty acids. That’s kind of where that comes from.

This is one of the studies that does highlight that pretty well. And we do know that these short chain fatty acids are really beneficial for gut health. So seeing a reduction in those is a negative thing. It was suggested that this was for a couple of key differences though. One of the key differences was that these bodybuilders did have a higher protein intake than the other two groups, the runners and the control groups. So we’re looking at on average 236 grams of protein per day amongst the bodybuilders, 103 grams per day in the runners and 70 grams in the control group. So the bodybuilders were eating a significantly higher protein diet than the other two groups and that’s definitely one of the reasons that we may see this difference.

But there are also two other things that could be contributing here. So bodybuilders, their overall protein to carb ratio, so how much protein they were having in relation to carb intake was double the other groups. So they were having quite a fair bit amount of protein more than carbs than the other two groups. And the ratio of those two things, the people that did this research and wrote this paper thinks that could be playing a large role in why we’re actually seeing this reduction in overall gut health in this particular group. And then the third and what I think is going to be one of the more important things for sure is that whilst the bodybuilders had the highest fiber intake amongst all three different groups, it was only by a couple of grams per day. It was only 19 grams per day on average.

Aidan Muir:

I found that wild. So you’ve written a blog post on this. So I had read the numbers and I was like every group seemed to have really low fiber intake.

Almost like uncommonly low fiber intakes. Even the bodybuilding group was like 19 grams over. I can’t remember their calorie intake, I think it was over 3,000. I recall the runners was quite high as well.

Leah Higl:

Yeah, it was a quite high calorie intake and bodybuilders were looking at ~400grams of carbs on average and 200-

Aidan Muir:

Yeah, they weren’t low carb.

Leah Higl:

Yeah, they weren’t low carb either. So yeah, that was quite interesting because their fiber intake was really low. So general recommendation for fiber intake in men would be 25 to 30 grams per day, ideally more around that 30 gram mark per day. And these guys were eating so much and only getting 19 grams in per day.

Aidan Muir:

I was also imagining in my head being where are their calories coming from if that’s happening? Is it just a lot of rice?

Aidan Muir:

Rice, yeah. I was thinking are they having chicken, rice and minimal ish kind of vegetables?

Leah Higl:

Yeah. What these researchers put forward at the end of their paper is that potentially the fact that their calorie and protein intake was so high in comparison to a very low fiber intake. So the combination of those two things is probably what is playing the biggest role in the overall reduction in gut health rather than just the standalone high protein diet by itself.

The second study we’re going to go through is actually from 2014 and they took a group of rugby players and had a look at their protein intake and their gut microbiome diversity. Again, I’m pretty sure this was through fecal samples, stool samples as well. And they found that as protein intake in these rugby athletes increased, the gut microbiome diversity actually also increased alongside with it. So kind of showing the opposite of what you would think based on the findings from that previous study. So protein intake went up, so did the diversity of their gut microbiome. The biggest difference between the diet of these rugby athletes as their protein intake increased and the bodybuilders in that previous study really came down to the carb intake and the fiber intake.

The rugby athletes were having a higher relative carb intake to their protein intake and they were having adequate, if not more than adequate fiber intake. So there were other dietary changes happening alongside that increase in protein intake. So that kind of tells me that whilst a high protein diet with very minimal or subpar fiber intake could be not so great for gut health, if you add in a good fiber intake and an overall good quality diet, it probably doesn’t have that much of an impact. It’s probably at least neutral. If not, the outcomes of that particular study, there were people that their gut microbiome got more diverse so there could even be a positive impact happening in the right circumstances.

Aidan Muir:

I also think although that is only two studies, it is a decent summary of the research and it makes me think that if anybody is speaking with extreme confidence saying that high protein diets do negatively affect gut health or they do not have any impact on gut health whatsoever or they improve it, so to speak, I feel like it’s hard to speak with extreme confidence.

Looking at it through the lens of being based on the research that we do have, what would be some appropriate recommendations if you were concerned about this? And it is enough for me to not necessarily be concerned, but it is enough for me to be like I would take these steps that I’m about to recommend. The first one is if you’re eating a relatively high protein diet, I believe you should also be consuming a relatively high fiber diet. I think most people should already be aiming for a relatively high fiber diet, although there are some exceptions. But because a lot of the general recommendations we often hear are say 25 to 30 grams of fiber per day, I think it should also scale based on your calorie intake.

And this is something that we both agree on because you came to the same conclusion in your blog post as what I came to being. I think 12 to 15 grams of fiber 1,000 calories is a relatively good target because that therefore means if somebody’s eating 2,000 calories and they’re at the top end of that range, they’re at 30 grams. If they’re having 3,000, they’re at 45 grams, which I don’t see think is obscene. I do question the top end of that range once we start getting to 4,000, 5,000, it can’t turn into fiber.

Leah Higl:

Yeah, it probably caps out.

Aidan Muir:

It particularly makes people struggle to eat a lot of food and stuff like that. But that’s why I like the 12 to 15 gram range because it kind of means you can scale it as you increase calories. So 12 to 15 grams per 1,000 calories probably a good target.

I also think that aiming for a diversity of plant-based foods is a good idea for many, many reasons. One for diversity of bacteria and also maybe from the perspective of managing IBS symptoms in a way in that say people who follow body building style diets leading up to prep where they eat the same thing over and over and over and over, I do think one of many factors in why they get IBS symptoms often post show is because they followed a meal plan that has just the same foods over and over and over and they haven’t exposed their bacteria in their gut to upper foods for quite some time. It’s a little bit speculative, but I don’t think that’s too far of a reach to look at it that way. And at minimum, we know from this whole diversity of bacteria, it’s a good idea to be having diversity of plant-based foods as well.

Leah Higl:

Yeah. So overall thoughts. My summary I suppose from looking into all of this and looking at the research that we do have is that the health effects of an increased protein intake or a high protein diet and that protein fermentation that happens in the gut, not entirely clear, but having a really high protein diet with low carb intake, low fiber, low plant diversity is probably harmful to the gut microbiome, probably not great for gut health. So for those who are on a high protein diet, if gut health is something you are interested in looking after, get adequate fiber, like you were saying, kind of scale it up as needed, maybe potentially a higher carbohydrate diet kind of plays into it. Usually carb based foods are going to be your fiber rich foods as well. And again, high plant diversity.

Aidan Muir:

This has been episode 77 of the Ideal Nutrition Podcast. As always, if you have not already, if you could place leave a rating and review, that would be massively appreciated. But apart from that, thank you for tuning in.