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 146, where we’re going to be talking about intermittent fasting and whether it is bad for muscle growth. So just to keep things simple, we’re largely going to be referring to 16:8 type approaches for fasting. Although other options exist, you would just make an assumption that anything more extreme than this, the same things we’re talking about, we’ll just apply on a larger scale.
So we’re just gonna try and keep it simple by talking about this, but same concepts can apply. And we’re gonna be looking at this from two angles. We’re going to be looking at it from the theoretical perspective. So if total food and exercise was matched, what do we think would happen based on the research we have? And then also the practical approach being like, what typically does happen with this?
Leah:
The main reason most people would propose that intermittent fasting would be bad or a negative thing for muscle growth is mostly around the protein distribution being limited. A great paper from 2018 titled, How much protein can the body use in a single meal for muscle building implications for daily protein distribution? My gosh, I need to take a breath after that. Concluded that if you want to maximise muscle growth, you should aim for 1.6 to 2.2 grams of protein per kilo body weight per day, split over four to six meals that are pretty evenly distributed. This is a great paper for several reasons.
One is that although it provided that specific recommendation, it also explored a lot of areas of protein research. It looked at higher versus lower frequencies, as well as different intakes of protein. It explored things from both an acute muscle protein synthesis point of view, but also looked at longitudinal muscle growth, which is important because realistically, we care more so about muscle growth then we do acute muscle protein synthesis.
Although you could argue that the more you are optimising muscle protein synthesis across the day, hopefully that equates to longitudinal greater muscle growth. It also touched on how larger amounts of protein in one go will likely keep the muscle protein synthesis elevated for longer. So again, kind of playing into that. Reading through all the references, it did stand out how few longitudinal muscle growth studies that were actually included in that overall analysis, which is really interesting because like I said, at the end of the day, that is what we care about.
Aidan:
That’s one of the few papers that I have read multiple times over the years. And that last point you said really does stand out because it’s kind of like that paper is one of the biggest ones we’ve got on protein distribution. There wasn’t that many longitudinal like longitudinal muscle growth studies that were included in that. And it stands out just because like one there’s not heaps of research looking at that. It’s interesting how confident a lot of people are when talking about this type of stuff. We’d assume there’s more kind of based on that. Pros and cons though, because part of the reason why it makes a lot of sense to look at acute MPS versus longitudinal muscle growth as well, like they both matter and make sense to look at both, but longitudinal muscle growth studies can be skewed by so much stuff, particularly if there’s a small sample size being used.
Like some people are just better at building muscle than other people. It’s like, And you would see that in small sample sizes and you could potentially make decisions that are incorrect based off of reading research on that. But the other end of the spectrum, like we do need research on that because that’s what we care about. Like if the goal is to build muscle, we need research on that.
So I know a few thoughts on that. That is just interesting, just like when looking at nutrition and training research in general. But let’s take the other angle of looking at the protein distribution side of things, because we’re probably gonna spend a decent chunk of this podcast on protein distribution, because it’s the thing that is clearly the most affected by intermittent fasting from the theoretical perspective. So from that angle, research looking at intermittent fasting approaches in a calorie deficit with appropriate calories and protein typically find that people retain muscle pretty well.
A lot better than a lot of people who are really big on the protein distribution thing would think. In a lot of cases, we can’t even see the difference between people on intermittent fasting approaches and those on protein distributed approaches in a calorie deficit. I’ll talk about why I specify calorie deficit a lot later, or we’ll come back to that, but that’s a key thing to be aware of. It’s like, okay, this clearly people aren’t losing all their gains by going on an intermittent fasting approach. Like total protein and calorie intake are appropriate. It seems to be fine from that perspective.
Another study that came out relatively recently, so we’re recording this in 2024, this came out end of 2023. It was titled, the anabolic response to protein ingestion during recovery from exercise has no upper limit, very ambitious title, in magnitude and duration in vivo, so in humans. This study involved 100 grams of protein ingested post workout, it a pretty tough session, from my understanding as well, versus 25 grams post workout.
It found that the anabolic response to the higher amount of protein was more significant and of greater duration than the 25 gram amount. This study made waves. I personally did an Instagram post on this and it was like my second or third most engaging post of 2023. Crazy. Yeah. And like I saw a lot of other people talking about it, like pretty much like most people in the fitness space and the nutrition space did make some form of content out this.
It was a big deal, many people viewed it as groundbreaking information, but honestly, that surprised me. One of the things I did, I don’t think anyone cares about this, but one of the things I did was like, I found a post of me in 2018 being like, I’m saying the same thing after this, I’m saying the same in 2018, like just shared my story. Because even that review we just talked about, was from 2018 and that review was reviewing previous studies and had come to a conclusion about little things like if you have a larger amount of protein, muscle protein synthesis likely will remain elevated for longer.
But anyway, I wanna touch on like why it kind of surprised me that this was groundbreaking information, even though it does add a really valuable piece. It’s kind of both, it’s not groundbreaking, but it also adds a valuable piece of information because we hadn’t really seen anything demonstrated this clear cut. But previous studies have touched on the idea that larger amounts would keep muscle protein synthesis elevated for longer due to things like digestion time. This also applies to things like the anabolic window in terms of protein pre versus post -workout. If had protein pre -workout and you trained for one hour due to digestion time, you will be having muscle protein synthesis elevated by the protein you had pre -workout. These things still apply.
Two, total protein intake has always been the priority. Something you touched on just before, Leo, was that the conclusion of that distribution study, it was aiming for 1.6 to 2.2 grams per kilogram of body weight protein per day And in that study, they mentioned to hit those numbers and spread it out over four to six occasions across the day, this would dictate that you would need to go 0.4 to 0.55 grams per kilogram body weight protein per day. I’m gonna simplify that, that’s a lot of numbers. It’s like 20 to 40 grams of protein, four to six times per day to hit those numbers. But the total protein was the clear thing.
Some people say that there’s arbitrary limits, like you can only absorb 30 grams of protein. Imagine saying that to like a big footy player. And then like you might have them suddenly not even hitting enough total protein intake, is clearly the priority. Next one, intermittent fasting research has long shown that muscle retention seems fine. That was something I talked about earlier. That would not make sense if distribution was the be all and end all. We would not be seeing these outcomes in these retention studies.
Leah:
Yeah, I think like that particular study when I first read it, I was like, it doesn’t change my opinion. Not that groundbreaking, but an interesting piece of knowledge nonetheless. It’s a good addition to the research. It’s a good addition. But then I saw it popping off on social media and I’m like, okay, I think people are slightly mis slash overinterpreting this in a way that’s making it sound a bit great groundbreaking. And I think I still have that opinion now, like after looking into it a bit more and thinking about it a bit more.
So some people have insinuated that it means that a hundred grams of protein in one go would work as well as taking a hundred grams and then splitting that up four times across the day. That’s not really what the study even really looked at. It was comparing a hundred grams of protein versus 25 grams of protein. And then obviously, assessing muscle protein synthesis. But who’s to say 35 grams, 40 grams of protein wouldn’t have been better than 25 grams of protein.
So there’s like, there’s like so much grey space in between 25 grams and 100 grams of protein that could give us more insight into what would ultimately be optimal from a muscle protein perspective.
Aidan:
And why I say this like adds to the research is like, what if they had done 100 versus 50, sorry, 100 versus 50 versus 25. And we see that 100 kept muscle pressure and synthesis elevated at a higher level for longer. But what if 50 came out exactly the same as 100? Yeah. We don’t really have that clear information. We can make some guesses based on what we have, but we don’t have that very clearly, which is why I this adds a lot. There’s still gaps left.
Leah:
Yeah. And I think with the 25 gram number specifically, if we think about that study where it was like, you know, having 0.4 to roughly 0.6 grams per kilo body weight per meal is a good amount in terms of distribution. It’s like 25 grams for like a guy that’s like 100 kilos. Like that’s gonna be on the lower end of that or even suboptimal in that regard. So it’s like, there could very well be quite a similar response to like 40 to 50 grams of protein as there was 100. So I think like 25 is like cutting it short for a lot of people.
Aidan:
Yeah, there’s also one rogue study out there that I think it was older, older individuals. And I think they did do a training session. This probably won’t be listed in the show notes, but it is a real study, believe me. Where muscle protein synthesis, like they gave them like 70 grams and it still was beneficial versus a lower dosage. That’s a huge outlier. And people point to you like, was it the training? Was it their age? Was it whatever? But even people looking at it from the perspective of like an arbitrary limit, like 30 grams, there are studies that do still exceed that from the acute muscle protein synthesis thing as well as factoring in all this longer term stuff that we’re looking at as well.
Leah:
Overall, it would be wild to base every decision completely off of the perspective from that one study.
Aidan:
And even though I say based on the research, intermittent fasting has worked pretty much equally well for muscle retention while under calorie adjusted, assuming protein intake is accounted for. I personally wouldn’t risk it if I was working with a competitive bodybuilder going through a comp prep, just because the risk of muscle loss is so much higher late in prep.
And it’s hard to say if this same thing would apply when we’re looking at people dieting under very different conditions. Maybe it comes out equally, maybe it doesn’t. I just personally wouldn’t risk it. That’s my own thoughts, which kind of tells you a little bit of what I think about the muscle protein distribution thing. But we’ll come back to that a little bit more. We’re gonna go through a few other things because there are still other gaps in the research.
One of the biggest logistical difficulties we have when we’re looking at protein distribution and how much it matters, because I kind of think it’s like a 10 percenter, one of the biggest logistical difficulties is it is super rare for intermittent fasting studies to involve muscle growth. If you look at all of the research, it is very rare.
Usually the participants end up in a deficit. I’m just gonna cherry pick one study. We can talk about more as a whole, but cherry picking one study just to kind of make this point. This study was titled time-restricted feeding. You can find this in the show notes. Time restricted feeding in young men performing resistance training, a randomised control trial. So it’s an RCT. We love that. It’s from 2016.
They did eight weeks of resistance training. The non -time restricted feeding group gained 2.3 kilos of lean mass. The time restricted feeding group gained zero kilos of lean mass after eight weeks of training. And that’s partly just because their reported intake decreased by 650 calories per day. Like when people do intermittent fasting studies or when they enter a study like this and they’re fasting for the first time, typically their intake does reduce. And we know that to optimise muscle growth, you probably want a small calorie surplus or you want a calorie surplus.
Leah:
Looking at some other research, a 2020 systematic review found eight studies looking at intermittent fasting and resistance training. Seven out of eight of these studies showed no significant muscle gain or loss. Only one of them found muscle gain. In that particular study, they gained 1.2 kilos of lean mass over eight weeks which was pretty impressive and also the same result as the non-time restricted eating group.
So it seems that the fasting group didn’t suffer any like loss of muscle or weren’t able to put on as much muscle as much muscle. So that is an interesting thing. The tough thing here is that there is literally just the one study showing significant muscle growth. So that in isolation is a little bit hard to interpret. Obviously we wouldn’t base all of our opinions on nutrition off of one particular research study, but it is interesting to note nonetheless.
Even still like it is still a bit tough because sample sizes are going to skew things specifically due to genetics, where we can see that skewing things in studies quite a lot. Then you also have adherence of the participants adding in a whole new variable.
Aidan:
Yeah it’s just really rough to compare, like what would make this process easier is if we had massive sample size studies with people in intermittent fasting groups, in a calorie surplus and then other people distributing protein over 4-6. Like it would be incredible if we had that.
Leah:
We are asking for alot.
Aidan:
Yeah. So it’s really hard to say whether one like it’s hard to even actually get to the crux of problem being like, is intermittent fasting bad for muscle growth from a theoretical perspective? When we don’t really have that information to really fairly compare. So a lot of it is just interpretation, trying to interpret the research and come to a bit of a conclusion. So now let’s talk about practical stuff, because that’s the summary of the theory.
From a practical perspective, it can be tougher to consume sufficient calories and protein if intermittent fasting. That’s why all these randomised control trials we’re looking at did not result in muscle growth. They just largely went into a calorie deficit. Another thing that I’ve personally noticed, because I just want to answer this question myself just out of curiosity, not because I’m interested in trying it, but just because I like to know stuff, is another thing I’ve noticed is that there are plenty of people in the real world who’ve been able to gain muscle while doing intermittent fasting. My anecdotal observation is that a lot of the people who have done it typically are people who have been intermittent fasting for a long period of time, as in they started it, they went into a calorie deficit, they lost a decent amount of size, they found a new baseline, they’ve been doing that for a while.
Then they change some stuff to get some more calories in while doing intermittent fasting. Often they’re doing it for unrelated reasons. Like they’re just like, I just find myself more productive because I don’t have to stop to eat and stuff like that. So you definitely can gain muscle, intermittent fasting, just because we’ve only got one study that actually showed muscle gain doesn’t mean it’s like this rare phenomenon. Like it’s something you can definitely do. The reason we’re just looking at research though, is to kind of be like, how does it stack up? Like if all other factors were equal, how would this play out?
Leah:
Some other quick thoughts and things to consider. A big one is kind of training timing. So that can be a lot more relevant if you are taking on an intermittent fasting approach. Some people love faster training and that’s fine. But if you’re looking to optimise performance, particularly in hard sessions that are quite glycogen depleting, it probably does make sense to have something to eat beforehand.
So if we’re talking intermittent fasting, you probably want to train somewhere in like your, your eating window or be able to have something pre-session so that you’re able to push and therefore add stimulus to the muscle and hopefully grow more muscle that way. The anabolic window is also kind of a thing. Like it isn’t this very short period of time post-training that we once thought it was.
It is more of like a three to five hour block around your training session where you can consume protein to optimise the recovery and muscle protein synthesis post that session. But it’s still good to have some protein obviously around your session. So again, if you’re timing your training session in first thing in the morning, you’re not eating beforehand and then you’re also not eating for several hours after until you start your eating window, then that could put you at a disadvantage from a muscle building recovery point of view.
One option here, if you don’t wanna stop intermittent fasting is having, or change the timing of your training session, is having a modified fasting window where you still outside of your fasting window have a little bit of protein or maybe a little bit of carbs pre-training as well to offset this negative impact of intermittent fasting. So it really depends on why you’re fasting and what you would like to do to kind of overcome that downside.
Aidan:
Yeah, cause like if somebody was just doing it cause they’re like, it just saves me heaps of time like a protein shake could be super quick and like, would solve this problem. If some people love the mental clarity of it or whatever, you could try it, see how it feels. If you’re doing it for, autophagy related purposes, that’s another discussion. Like there’s so many things to get into there, but it just, it really depends on why you’re doing it.
So I’m going to go through a bit of a summary. So fasting has some logistical challenges, and some theoretical things that make it so that might not be as effective for muscle growth. I think of protein distribution as a 10 percenter. Total protein intake matters far more. I think protein distribution is a bit of a 10 percenter because one, like the muscle protein synthesis acute kind of data, but then two also the anabolic window, like if you’re distributing protein, you’re probably going to take care of that without even thinking. Keeping in mind that when I say anabolic window, it’s the exact same thing Leah was talking about where it’s like, it’s not this like nice small window. It’s just something that kind of matters.
And like there’s a decent period of time around training, but it’ll be taken care of versus the alternative about maybe training in the morning and then not having any form of protein to like 2 pm for example. So that’s a bit of a summary. Other stuff though is as I touched on, there’s not research fairly comparing it being like from that longitudinal perspective, it will be very hard to get research comparing that for the logistical reasons, for sample size reasons. But the fact that as we touch on, there’s not even heaps of stuff looking at longitudinal muscle growth with different nutrition interventions anyway. There’s still some, but there’s not heaps.
But my own personal summary. If I was obsessed with muscle growth and trying to do absolutely everything I could and nothing else mattered to me, I probably wouldn’t do intermittent fasting just based on everything that I know. Even though I protein distributions are 10% or whatever, it’s like, well, if I was obsessed, like I’ll do the 10% or if that makes sense. But on the other end of the spectrum, I wouldn’t be scared that it is impossible to gain muscle doing an intermittent fasting approach. If I was somebody who didn’t have much muscle mass, loved fasting, and I was like, want to some muscle. I wouldn’t be like, damn, I can’t fast anymore. it’s like, you can still gain gain muscle with these types of approaches as well. It really just depends on priorities and what you’re specifically trying to achieve and why you’re doing it in the first place.
Leah:
This has been episode 146 of the Ideal Nutrition podcast. If you haven’t yet left a reading or review, it would be greatly appreciated for you to do so. But otherwise, thanks for tuning in.