Aidan:

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 183 where we’re going to be talking about the topic of gut health and weight loss. There’s very clear links between gut health and overall body weight on average. It’s not really a debated fact that there are common trends, like it’s pretty clear. But the more complex topic is how much is it linked? Does implementing gut health specific nutrition directly contribute to weight loss?And does losing and or gaining weight change gut health by itself? Or is it just the behaviours associated with that processes that influence gut health?

The next layer, which we have spoken about previously as well, is that gut health has two kind of separate definitions, which can overlap a little bit. The first one is a lack of gut symptoms could be defined as good gut health. For example, if somebody had IBS symptoms, they might call it bad gut health. That’s one kind of definition. The other one is far more specific to the populations of bacteria living in the microbiome and the trends are associated with that. For example, certain populations are more associated with good overall gut health or good overall health. And similarly, when we’re looking at obesity versus lean individuals, there’s certain population trends that you can see. In this episode, we’re largely referring to that latter definition related to about populations of bacteria, even though there is overlap of the two of them.

Leah:

Now we’re going to get into some of the research surrounding this particular topic with the caveat of we obviously aren’t going to cover every single study on this topic because it’s such a broad area of research that we could potentially look at. But I think what is going to be more helpful or create at least an interesting narrative for us to explore for this podcast is looking at three particular studies that look at this topic in different ways and have found interesting outcomes, I suppose.

So study number one is where they took 77 pairs of twins. It’s crazy that they found 77 pairs of twins. That’s incredible. The next one is also more incredible in that in each pair of twins, there was one that had a BMI in the obese category while the other did not. So we’re also looking at like very specific sets of twins, where there is that discrepancy. And in those results, obesity was associated with lower gut bacterial diversity. But in this case, like we’ll cover more about this, but it is like bit of a chicken or the egg. Obviously we don’t know kind of what direction that goes in, terms of causation.

Study number two is what we’re gonna recall, call the famous mouse study. And basically, in this particular study, they were using feacal transplants in mice that basically added the microbiome from one mouse and found that it could actually create obesity in another mouse that didn’t already have that going on. So they’ve kind of concluded that if we transfer this over to people, like if we do a feacal transplant in a person who is obese to someone who is not potentially that could result in obesity becoming present in that second person receiving the feacal transplant. So again, that’s a really weird one, but I think it’s something that is particularly interesting.

The third study is two groups that were separated by their microbiome characteristics and given the same diet. So one group had more Prevotella and then the other group had more bacteroides. The group that had the more Prevotella lost 3.5 more kilos of fat than the other group. and studies like this have been used to promote the idea of like personalised nutrition when it comes to weight loss and obesity but that is a bit more of a speculative link at this stage. As a bit of a side note, if research consistently found this, it’s probably more of a prediction of rate of weight loss rather than indicating that different dietary approaches are superior for different gut microbiomes. But overall, there is a long list of interesting studies. We just wanted to touch on a few that kind of highlight the different interactions that the gut microbiome and gut health may have with obesity and weight loss.

Aidan:

And no matter how broad you go with the research, it still has to come back to that energy balance model in some way. We know that calories in versus calories out has to play a role. We have spoken about that so much that I don’t think it’s worth explaining again. But if we look at it through that perspective, this stuff has to have an influence over calorie intake or calorie expenditure. There is a slight tweak that I’ll say on that though, in that on the intake side, or I suppose it goes on both sides to a degree, on the intake side we could also be talking about absorption of calories.

For example, if somebody had a difference in their gut microbiome that allowed them to absorb more calories, that would increase calorie intake and potentially link to increased rate of weight gain. The alternative end of that spectrum is it could change thermic effect of food to a small degree as well. If we’re looking at that absorption side of things, and we use two angles, I reference this quite a bit but almonds, we typically absorb about 70 to 80% of the calories in almonds. What if one person absorbed a lower percentage and somebody else absorbed a higher percentage? That is a relevant difference there. And that could partly be explained by differences in the microbiome.

The other one is fibre. So fibre contains calories. We talk about it through the lens of us not digesting fibre, but certain types of fibre, particularly soluble fibre can have a fermentation process that goes on in the large intestine where bacteria does absorb calories. Fun fact, but in Australia, we count on nutrition panels, fibre is around two calories per gram. We count carbs, protein, both of those are four calories per gram each and fat is nine. So in Australia, we actually do count fibre as calories. It’s more just like speculative about how much it contributes. And on an individual basis, there would be a difference as to what you’re absorbing or what your bacteria is absorbing of the fibre.

The other stuff that is very likely to be more relevant is changes in appetite regulation. So gut bacteria can influence hunger and fullness. And this could change intake even in the same environment. Like if we go back to that mice study that was referenced earlier, the mice were in the same environment. They the same access to food and exercise. And that could be another small explanation for that as well. You could also be talking about changes in energy expenditure. For example, changing the microbiome could reduce energy expenditure or it could increase energy expenditure as well. I have not actually seen many slash any solid explanations or research identifying that type of stuff, but it is worth being open-minded and considering that that could be a relevant factor as well.

But with all of this, I did want to tie it back to that kind of calories in calories at model because they’re not necessarily separate things. It’s not like one matters and the other doesn’t. We talked about a funny example in the podcast back looking at that gut health documentary on Netflix where they have the line, what do they say, count, always be counting in terms of plants. Variety of plants, always be counting, not calories, plants. And I’m like, can’t you focus on both? It’s not like one or the other. the models can fit together and they are both clearly relevant. And if we had to only focus on one, we do see the calorie model having a big influence on weight loss. That is a big thing, even though both can be relevant.

Leah:

Yeah, it’s like we know like calories in versus calories out is such a complex model that the gut microbiome is like potentially just one piece of the puzzle that fits into that like overall model, right?

Aidan:

100%.

Leah:

So moving on to interpreting the overall body of research and kind of coming to a bit of a conclusion where we can. So there is clearly a link here. The bigger question is how much does this matter and what aspects are actually practically relevant? I’ve never seen any individual approach significantly outperform what you would expect based on other models of weight management involving calories as we spoke about. So clearly like this particular topic is not the be all and end all. It’s obviously bigger than that.

Aidan:

Let’s even like go deeper on that. Like if you look at all that research on like low-carb diets versus low-fat diets with calories matched. Like if the gut health stuff was making a huge difference, we would probably expect to see differences in gut health with the low-fat versus low-carb, particularly over those time frames.

We know we can shift the microbiome pretty quickly. We know that there’s these metabolic ward studies, there’s the, there was at least one study done that was done on a low carb diet versus a low fat plant based diet, which would have had a huge difference in the influence on gut health and weight loss was the same in both of those groups. I know it’s pointing to just individual things, but it is coming back to like how much could this matter to a degree?

Leah:

100%. And this might be a poor example, but just pointing out like one thing is that when probiotic supplements are studied and weight is a factor that is measured, every now and then we do see like maybe a little bit of like a difference in weight loss, so like maybe a kilo or so, but it is really like that significant difference. And it’s like, kind of goes back to what you were saying with those particular studies. Like when we use different dietary approaches for weight loss with calories matched, we do sometimes see like these small discrepancies, but it’s not like a consistent significant difference, right?

On another note, we consistently see high fibre intakes being linked with lower body weights. But this is also explainable by things like reduced calorie intake due to satiety and also often choosing foods that are less calorie dense as well. So it’s not just this direct impact, but the indirect impact as well.

So as a little bit of a summary, that is focusing on specific interventions. So things like fibre and probiotics, but in a similar fashion with dietary patterns that are linked with better gut health in the cases where weight loss is relevant, they typically also involve a reduction in calories. And that’s something to kind of factor in there. And then if pointing to hormonal changes in relation to gut health, like that may, might also make sense. But even the changes in intake could be explained more directly with things like fibre and food volume.

Aidan:

Yeah. A semi unrelated thing that I saw somebody probably was like 10 years ago. So somebody says, but they made the point that they’re like, let’s say probiotic supplementation improve your digestion and it helped with your absorption of food. Couldn’t that theoretically lead to weight gain? And I was like at the time, I like, that’s actually an interesting question. One thing we know very confidently though is that does not happen. Like we do not see that. Like we see either no change in weight or we see that very, very, very small change in weight in the decreasing direction.

So that’s something to also factor in with this whole absorption thing that was talked about. Cause like theoretically improving gut health could improve absorption, but it is never from what I have seen led to an increase in body weight. But what I’m going do now is just do a bit of a summary and what I’d call what to do with this information. So bit of a summary is even without clear information how much this matters, because I do think it matters to a degree, the next steps are very clear. Step one, keep the basics in mind. Have an awareness of calories. This doesn’t necessarily mean tracking. It just means don’t ignore calories to solely focus on gut health, because that is something that we do see out there.

Step two, do the things that are good for gut health. Everyone should be doing this. At a minimum, this will be good for general health anyway. To do this, if I to really simplify down to some stuff, one, the always be counting thing, the aim for greater than 30 different plant-based foods per week is a very standard recommendation that I give to almost everybody. Have a good dietary fibre intake. Probiotics are an option. It very likely makes sense to include some form of fermented foods that are high in probiotics naturally, but there are also some cases where we would consider recommending an actual probiotic supplement as well.

We’ve got separate podcasts on that. You could go and find them just by Googling and prioritise a wide variety of nutrient rich, minimally processed foods. So those are core messages that typically would give to almost everybody to start off with, but that would help with gut health as well, which if it is playing a decent size role in this stuff as well, it will help with that stuff too.

Leah:

This has been episode 183 of the Ideal Nutrition Podcast. If you liked it, please leave a reading and review, ideally a positive one but otherwise, thanks for tuning in.