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 218 where we are going to be talking about body composition outcomes on low versus high carb diets and the concept of whether it matters if calories are matched for those two things. So, I often talk about this concept of like calories and protein being matched and get a lot of people like asking what that means.
I’m like, I wish I had a simpler way of saying this. Basically what I’m saying is like, let’s say hypothetically you are on 2000 calories and 140 grams of protein. You can feel that the rest of your diet with carbs and fats, you could have more carbs and less fats, or you could have more fats and less carbs. That’s basically what I’m saying being like, if have the calories the same and the protein the same, but the only difference is the carbs and fats, what happens, basically?
And we’re talking about that from a body composition, both in terms of muscle gain and also in terms of fat loss. I think we’re going to really focus on what if calories are truly matched and everything like that, and we’re looking at research in controlled environments and stuff like that. And we will also talk a little bit about in the real world, because sometimes there is some stuff that will pop up in the lab that isn’t necessarily applicable to the real world as well.
Leah:
Starting off talking about the theoretical stuff when it comes to fat loss and being in a caloric deficit. So, in a calorie deficit, it’s quite simple, it’s quite clear. The split of protein and carbs doesn’t really seem to matter. Again, as long as protein and calories are appropriate. If we have a high enough protein intake that is protecting the muscle mass whilst in a deficit, the body is then forced to fuel or cover that deficit by utilising other internal stores, mostly your glycogen and your fat stores.
Since energy stores in the form of glycogen are relatively limited, we kind of run out of those fairly quickly. And then we have to rely on our fat stores, which even when you are relatively lean, there is going to be quite a lot of energy that we can pull from the fat stores specifically. So if somebody was consistently in a deficit over the long term, the majority of that loss would need to come from fat, again, given that protein is high enough to preserve muscle mass.
And then we know that energy expenditure on a low fat diet versus a low carb diet, again, calories and protein matched, doesn’t differ much. So, again, that’s not really a factor we’re going to need to take into account here because they seem to be relatively the same. And we’ve previously spoken on the podcast about things like higher versus lower insulin levels in low versus high carb diets. But again, not making a noticeable difference when it comes to fat loss. Once again, when calories and protein are matched.
Aidan:
Cool. So that’s a good theoretical summary in terms of like specific research using calorie match stuff. These, as you can imagine, are harder for researchers to do to a degree than like real world ones because really they’ve got to get people together, provide all the food, make sure their energy expenditure, like say they’re doing either the same amount of exercise or no exercise. And the longer you go for, the harder this is. Let’s say you do a seven day study. Are you having people take seven days off work? How could you do like a year long study?
Like you can see why, like these studies are few and far between to a certain degree. But, the best summary we have of this is there is a review by Kevin Hall, who I feel like we quote a lot, I think it’s just because he has done a lot of research in this space, which I think is a very relevant space. And this review had 32 randomised controlled trials where they directly substituted carbs and fats for each other while keeping total calories the same. That is exactly what we want and exactly what we’re looking for. Are the gaps in the research? Of course there is. We’re not looking at elite bodybuilders and stuff like that here.
But this is as good as we can get from my perspective. And what he found was that fat loss came out the same when you did this, which is exactly supporting that entire like theoretical framework. So even if you were to somehow disagree with any point of the theoretical framework or anything like that that has been mentioned, you can’t really disagree with the results.
We have a lot of research directly looking at this and it has basically found that there’s no difference. This lines up with the rest of the research on the topic as well. And it holds true all the way from extremes. Like it holds true all the way from ketogenic diets through to low fat ones, assuming calories and protein and match. And the best bit about this is that we’re very fortunate that this means you can actually just do what you want. You don’t have to be tied to either approach or anything like that. You can just choose whatever works best for you.
Leah:
Let’s talk about some real world research and the outcomes and findings from that. So, there are quite a few real world type studies looking at comparing these two ways of going about dieting that often go for longer durations. And they do seem to come out relatively comparable when it comes to low carb versus low fat approaches, even when it’s like that real world approach. You will often find studies pointing a bit towards one direction or the other, but it’s not super significant.
If solely looking at weight loss, it’s pretty common for a low carb approach to actually outperform a low fat approach by about one to two kilos. But when you account for things like water and glycogen shifts in the weight differences, it actually typically ends up being the same amount of fat loss. So even though there is more initial potential weight loss like scale weight change coming from that decrease in glycogen and water weight, the amount of fat lost is very comparable.
The most relevant study in our opinion is one called the diet fit study where they had over 600 participants and had half of them go on a super low fat approach and the other half go on a super low carb approach. It was initially less than 20 grams of either fat or carbs at the start of the study based on whatever group that you went into, then essentially as low as you could maintain for the rest of the 12 months. So you didn’t have to be under that 20 gram mark, but just as low as it was feasible to maintain over that long stretch of time.
And then their findings were, not surprising at this point of the podcast, is that both groups lost a very similar amount of weight. As a key point though, nobody was actually in ketosis at the end of the study. So out of a group of over 300 people attempting to go as low carb as possible, they couldn’t sustain low enough carb to be in ketosis and nobody maintained less than 50 grams of carbs consistently long term.
So of course there are people out there that thrive on one approach or the other and they find one to be easier to be compliant to than the other. It’s something to factor in that maybe there is one approach that is a little bit more difficult. Even if the research hasn’t necessarily pointed to a slightly superior version in a lab environment, I think you can just choose whatever you feel like you’re going to be the most consistent with.
Aidan:
Yeah, I really like that study because of the large sample size and how it was set up and everything like that. And, saying that with that large sample size, fat loss on average came out the same. It also still does support the belief that some people will do better on certain dietary approaches and stuff like that as well, because in that study, there were plenty of people on both sides who lost 20 to 30 kilos. So, there people on the low fat who lost heaps of weight.
There people on the low carb who did that. And it is a lot of trial and error in the real world to figure out what works for you. Sometimes when I talk about this, the response I get from some people is that they’re acting or they think that I’m indicating that you need to go either low fat or low carb. And that’s not necessarily what I’m saying. I like to talk about the extreme so you can kind of do what you want. Because, what we’ve spoken about where it’s like, as long as your calories or protein matched, you could do what you want where it’s like, it could be a bit of a balance between those two things.
It’s just the reduction has to come from somewhere, either fat or carbs or a combination of both. Now we are going to talk about muscle gain because the fat loss stuff actually does, it does seem pretty simple. We’ve got pretty clear stuff there. For me, something that has been on my mind for over a decade now is that although this is very clear in the fat loss space from all the angles of like theory and research, we do not actually have what I would consider to be good research in good amounts of good sample size in the other direction of looking at muscle gain.
And I do find it a little bit odd that there is this gap there. And even in prep for this podcast, something that I did was search the names of certain nutrition people I look up to, and then search terms in relation to muscle gain, macronutrients, all of those kinds of things. Like really hoping to be can I find some more research? And there’s just nothing that like really fits what I’m looking for where we have this calories and protein match thing.
So that does change the format, which is why we’re going to start with the muscle gain research. Then we’re going to talk about theoretical stuff and what people do in practice because there isn’t that much on muscle gain. And this is even more relevant at extremes because I don’t know how many people listening to this might be thinking that they might’ve seen certain studies looking at muscle gain. I’m talk about what I mean. Using extremes.
There are a bunch of like ketogenic diet studies looking at resistance training and muscle gain. And you’ll often find that participants even maintain or lose muscle in those studies, the majority of them. The issue is simply that they’re not eating enough total calories. This doesn’t tell us that like if you have a calorie and protein match calorie surplus in a ketogenic diet versus a high carb diet that is calorie and protein match, they’re getting worse results. It’s just saying that they’re eating fewer calories because the act of aiming to be in ketosis is often leading to that.
At the other extreme, going super low fat can have hormonal implications. If we were looking at it men specifically, it could reduce testosterone, which might reduce muscle growth. So that could be a factor as well. But once again, we don’t have the fair comparison to actually see this. And given we don’t have those fair comparisons with decent sample sizes, with intake controlled, we’ll have to base it on other stuff.
Leah:
Which brings us to the theory component because we don’t necessarily have this research to pull from, we can really only make theoretical assumptions based on what we know and see in practice or anecdotally. The majority of experts tend to recommend high-ish protein intake, of course, muscle gain and protein makes sense. And then, 15 to 30 % of calories coming from fat and then the rest from carbs.
This logic, I think, makes sense. If you went below like 15 % of your calories coming from fat, again, you could have issues with hormones like reduction in the sex hormones like testosterone and oestrogen. And this could have a flow on effect to your ability to build muscle.
So we know that that’s problematic in this particular context. Even though research technically has found small differences in testosterone levels between 30 % of calories coming from fat and 15 % though, it’s hard to say if there’s like a practical difference in muscle growth. I think if you were to go really, really low and like these hormones were tanked and you weren’t able to train properly, effectively, you weren’t able to recover, then yeah, that would make sense. But we’re not really sure where that kind of falls off a cliff at this point and it probably does differ person to person.
It’s very context dependent, but I think it does make sense to not necessarily go below 15 % of your calories coming from fat. And since we want to keep protein intake high, there is only so much room left over for carbs and fat. Whilst we have leeway, I think it makes sense to have enough fats to support good hormonal health.
And then we can look at the rest coming from carbohydrates, which a lot of coaches and nutrition professionals will recommend this with the theory that if we have a high amount of carbs coming in through our diet, then we have plenty of glycogen storage to perform well in the gym. So the training intensity matters and the ability to actually train hard to stimulate the muscle for muscle growth.
This probably does happen better or more effectively with a higher carb intake. But again, it’s very context dependent because how many calories are we consuming? If there’s like just an abundance of calories, we probably have more leeway with the kind of percentage of fat to carb ratio.
If fat though was to like massively exceed that 30 % number, it is likely to, for most people to cut into the glycogen being available for training sessions to a significant enough degree that it would start to potentially impair performance and therefore domino effect onto less stimulus on the muscle.
Generally, how much this matters for muscle growth over the long term hasn’t, again, been tested at a large scale. We don’t really have research backing it up or kind of giving us a clear answer. We can’t make strong claims. From my perspective, I’m always leaning towards if protein is high enough, calories are adequate, mild surplus/maintenance, whatever we’re doing, then we’ve got enough fat to support hormonal health, and we’ve got enough carbohydrates coming in to support the training load you’re trying to do. Great.
But it’s so context dependent and it’s so individual based on, again, what you’re trying to do and what your lifestyle looks like.
Aidan:
And now some of the real world stuff. We’ll look at what people are doing in practice. I’d say the theoretical stuff definitely points to those ranges mentioned. That’s what I think as well. But the thing that makes it even more interesting is that that is literally what bodybuilders tend to be doing in practice. I’m not going to say there’s no bodybuilders who are exceptions to this, because there is. I see it all the time. I see it occasionally on Instagram and stuff like that. But a study looking at 385 competitive bodybuilders found that nearly 100 % of them had macro splits that came out within those ranges.
And they’re the ones who are optimising muscle growth like, and things tend to trend in the direction of what works. The fact that it’s nearly 100 % is a pretty relevant sign. I wouldn’t normally point to anecdotal or observational stuff like that. But given the lack of controlled research and combining it with the theoretical stuff, and then also looking at what the best people are building muscle are doing in practice, it makes sense for me to base things on that at this stage for thinking that that is roughly what would be at least semi-optimal or close to optimal.
Leah:
A little bit of a wrap up. So, for fat loss specifically, there is clear evidence that a wide range of fat versus carb ratios can actually work equally well if protein and calories are accounted for. The main thing is just going to be do an approach that you can be consistent with over a sustained period of time and that is going to be very individual. So the choice is actually in your corner, they’re both pretty equal.
From a muscle gain perspective, it’s possible that the same is true and that you actually have a fair amount of leeway in what you do, again, accounting for protein and calories at baseline. But, if I were going based on the information that we have at the moment, even if it’s anecdotal or more observational, I’d lean towards those ranges we discussed specifically for maximising muscle growth.
Aidan:
This has been episode 218 of the Ideal Nutrition Podcast. As always, if you have not already, if you could please leave a rating review that would be greatly appreciated.