Leah:
Hello and welcome to the Ideal Nutrition Podcast. I am Leah Higl and I’m here with my co-host Aidan Muir and today we’re going to be talking about meal timing and fat loss. Whether meal timing can affect fat loss can be approached from both a theoretical side of things, but also a practical side of things. And it’s definitely worth talking about both of these aspects.
So we’re gonna start with the theoretical stuff. We’re gonna talk through that, largely looking at if there are differences in results of meal timing for fat loss when calories are matched to isolate meal timing as the variable we’re looking at. Then we’ll touch on what actually happens on the practical side of things. Like what actually happens in reality when we change meal timing and manipulate that as a variable. So we’ll start with the theoretical and then we’ll go practical.
Aidan:
So deep theoretical stuff to jump straight into, but I’m going to talk about insulin for a little bit. So insulin sensitivity is higher in the morning. That’s a pretty consistent finding in research. Insulin secretion is better in the morning too. So research has found improvements in beta cell function. We also see shift workers as a bit of an extreme example where blood glucose levels and insulin are often affected, but is that due to the time that they’re eating or is that due to the sleep? Like it’s a combo of both, right?
So the same thing obviously is a variable in there. But going back to those first two points that are clear is like insulin sensitivity, insulin secretion, probably different in the morning. The thing is how much does that matter though? Like from a fat loss perspective, which is clearly what we’re looking at here, it just does not seem to matter. If we were to change it to being like from a metabolic risk perspective, if somebody had pre -diabetes and were the cost of having full type 2 diabetes, that topic matters a fair bit more. But purely looking at fat loss perspective, insulin resistance at most plays a small role when all other factors are equated for.
Leah:
So the next thing we’ll touch on is does breakfast play a role in all of this? So a lot of people will argue a ton of different things about breakfast being the most important meal of the day. We’ve mentioned in many podcasts that we don’t have strong feelings about people needing to have breakfast for a multitude of reasons. But some of the logic that is often used behind these arguments is one, eating breakfast can increase energy expenditure throughout the day by making you more energetic.
Two, eating breakfast kickstarts the metabolism or stokes the metabolic fire is a term I’ll hear a lot. Number three, eating late in the day increases fat storage since you aren’t quote unquote burning it off. If you’re more sedentary towards the end of the day, you’re sleeping. Number four, eating breakfast will mean you aren’t as hungry later in the day and therefore will end up consuming less calories. So we actually have recorded a podcast specifically on breakfast and whether it is important in general. And that’s episode 105 if you wanted to dig into this a little bit deeper, but to cover this in a more short form way, and I’m just going to like rapid fire our responses to these logistical mechanisms.
So one, firstly, breakfast does not noticeably increase energy expenditure on a day-to-day basis. There could be individual variations with effect on things like activity levels, depending on the person, but it definitely doesn’t, quote unquote, kickstart the metabolism. So that’s something that’s definitely overblown. Secondly, we are always burning calories. So when it comes to, if you eat more later in the day, then you’re just going to store more as fat.
Well, like realistically, we’re always burning calories. It’s not just when we’re moving and doing things. We have our metabolic rate that keeps our heart pumping and our organs working and all those things. We’re constantly burning energy even while we’re sleeping. So eating later in the day doesn’t necessarily mean we won’t burn it off because we are continuously burning calories. When it comes to weight gain or weight loss, what we are really looking at is calories in versus calories out over days, weeks and months.
And that is what is gonna have the impact on whether we are maintaining, losing or gaining weight. If you are eating in a caloric deficit, it doesn’t matter if you have breakfast or not realistically, like that in isolation will not move the needle one way or the other, even though there are a lot of people, you know, making these like kind of logistical arguments around how it could potentially do that.
From a hunger perspective, research actually shows that those who do eat breakfast on average have a slightly higher caloric intake. I think there’s definitely room for a lot of individual variation here. That’s not going to be true for everyone, but it is interesting that overall like research would suggest that people that eat breakfast and maybe who have a greater eating window tend to consume more calories than those who don’t. But for some people like adding breakfast can really help with appetite management and it stops them from consuming far greater calories later in the day.
So again, individual variation, it’s not a breakfast will solve all your problems or vice versa. So the crux of all of this is realistically nothing magical about breakfast that is going to specifically support that loss. It’s really on an individual basis.
Aidan:
I wonder how many people binge this podcast and listen to us back to back episodes. In the last episode, we did speak about breakfast stuff. So if you do binge this and you are hearing that like pretty much back to back, shout out to you. We appreciate you.
Leah:
Thanks for listening to us for so long.
Aidan:
I hope nobody else like really noticed that, but yeah, just shout out to those people. So the other thing I was going to talk about on that is the closest thing to a magical factor about breakfast, eating earlier in the day and stuff like that, that we can really find to kind of address is that the thermic effect of food is thought to be higher in the morning than it is in the evening.
There is a study that heaps of people in evidence-based space cite on this topic. It only had 14 participants, but it was done in a crossover design. So that kind of makes it as if there were like 28 participants in a way. And they found that the thermic effect of food was around 50% lower in the evening than in the morning. I don’t know how much I’d read into that with small sample sizes. 50% seems like a lot in a way. But the thermic effect of food is also approximately about 10% of our energy expenditure in a lot of people obviously I’ll differ based on heaps of things like how much protein you’re having, how much fibre, how processed the food is, the same things right.
But when you actually do the maths on it throughout the day just being like if a portion of your energy of your thermic effect of food was higher by or lower by around 50 % How many total calories different are we looking at like a hundred maybe like it’s not like it’s not really actually a big difference It’s not really a practical difference I think the actual act of reordering your day to try to take advantage of any potential thermic effect of food, which I personally actually believe would be a smaller difference in the situation. But I think restructuring your day would likely have a bigger impact on your overall nutrition than the reward that you would reap by any small difference in thermic effect of food.
Leah:
Yeah, it’s a little bit missing the forest for the trees, isn’t it?
Aidan:
Very much so. But also think it’s worth addressing too, like just being like this thing is out there. That’s just my personal thoughts on it. The next thing we’ll touch on, you kind of touched on as well the breakfast thing, but like small frequent meals to stoke the metabolism. I don’t know, have you seen anyone say that for a while? Like I just get that from like bodybuilding forums back in the day.
Leah:
It’s definitely fallen off, right?
Aidan:
Like it used to be huge back in the day. The fall off needs to be studied. But back in the day, heaps of people would say that. This is so easy to debunk from multiple angles though. So I’m just going to use two. So the first one is simply looking at the research. That’s all I need to say. Like a review looking at the topic of frequency of meals, found no noticeable difference in energy expenditure. That’s simple enough. If you look at individual studies, you might find small differences, but a review just looking at all of the research and then just taking an average has found no difference.
They also, the authors of that specific review, which you can find by looking in our show notes, which we’ve got on the website, in that review, they also highlighted some of it’s quite obvious, but it’s like short term or acute studies seem to find differences because of the thermic effect of food, which I just talked about, which is the calories burned in response to eating and digesting food. Like when you have some food, the thermic effect of food increases, right? And the logic is just like, you do that six times a day, you’re increasing that six times a day. But that’s actually very much more closely linked to how much total food you have.
And it just balances out over the course of the day if the total amount is equal. Anyway, obviously we could just, that’s just mechanistic. We could just jump back to like, just look at the overall research so we don’t see any difference, but the other angle, the second angle is looking at the other extreme. Like if we’re looking at like six more meals or whatever, it’s like, well, if we were going to expect to see a difference, we should be able to find a difference if we went to the other extreme. So we could just look at intermittent fasting research.
Leah:
Yeah. And intermittent fasting is before I kind of delve more deeply into that topic. Every time I talk about intermittent fasting, not being magical for fat loss, I always have people in the comments, like sending me, is it Andrew Huberman or Hubberman? Yeah, there is podcasts and I’m like, I still listen to it. I promise. I’ve looked at all the research and I still feel this way. Intermittent fasting realistically gets the same results from a fat loss perspective. We’re not going to go into the longevity stuff, but from a fat loss perspective, when total intake is matched, heaps of research has found this.
So it’s like overwhelmingly if we have a calorie matched diet, whether we’re intermittent fasting or we have a greater eating window, the outcome is the same. But using a specific example that takes it a step further, a study from 2017 looking at alternate day fasting versus continuous energy restriction with calories matched over a six month period found similar fat loss results in both groups. The alternate day group consumed 25% of their calorie needs on fasting days and 125% of their calorie needs on the other days.
The other group consumed a consistent 75% of their maintenance calories. If meal frequency in isolation noticeably affected things like energy expenditure, we would absolutely see it in studies like this. It’s just not something that we do see. So it is worth noting from a practical side of things that almost every randomised control trial that has done intermittent fasting without the extra step of making sure things are calorie matched has found significant weight loss results. So that was statistically significant.
So if we’re not matching calories, and we just look at what people do when they can kind of eat freely when they’re intermittent fasting versus not. Typically when they’re intermittent fasting, they end up eating less calories overall. So that is something that is still very worth mentioning as part of this, but it’s not that the intermittent fasting itself is like a magical tool that impacts the metabolism in some way that that’s what’s having that kind of weight loss result. It’s the behaviours that can occur from someone doing intermittent fasting, and then that leading to a lower caloric intake overall.
Aidan:
One other angle we’ll look at is protein distribution impact that could have on muscle versus fat ratio. Like we’re specifically talking about fat loss rather than weight loss. So theoretically, if protein distribution across the day helped with muscle retention whilst on the calorie test and you lost a similar amount of total weight, that would have an impact. We’ve addressed this a lot, but if you focus on acute research, looking at muscle protein synthesis, it would make you think that protein distribution is super important.
This is where these rules such as you can only have 30 grams of protein in a single sitting type things come from. That research is basically just looking at acute muscle protein synthesis response where they might give somebody 10 grams, 20 grams, 30 grams, 40 grams, and it peaks at a certain point. It’s been obvious for a long time that there’s flaws in that thinking. It has never truly lined up with what we see from more longitudinal studies where protein isn’t optimised with the distribution there. But I don’t wanna go too deep on that because we have spoken about that.
But what is super clear from this perspective is when total calorie and protein intake is matched under intermittent fasting conditions, people retain muscle quite well. They still retain muscle to what seems to me from my interpretation of the research to a similar degree as those who are having protein spread out over four to six meals in a calorie deficit. What I’d love to see that we don’t really have is research looking at muscle growth on intermittent fasting or during intermittent fasting because of what you said earlier, like almost every intermittent fasting study people end up in a calorie deficit.
There have even been a few studies I’ve seen that have been designed to try to measure muscle growth, the fasting group just ended up in a deficit and they just retained muscle. So for our specific question, it doesn’t affect fat loss. But it’s still, there’s still some stuff that I’d like to see in that perspective, but it doesn’t affect fat loss.
Leah:
Yeah, it’s like we need a randomised control trial that is calorie matched at maintenance or surplus. That’d be cool to see.
Aidan:
Yeah. And I think there is one that I’ve seen. It’s just like, I’m just not going to base everything I say on this podcast on one. Yeah. Like I want more. Okay. We need a few.
Leah:
Yeah. Now, okay. That’s the theoretical stuff and all that, but looking more at practical stuff. So what happens in reality when we adjust things like meal timing for fat loss. Meal timing actually has a huge role to play in appetite management but the crux of this is like an individual approach is always best.
I’d never, like, I don’t, I know you’re the same because we’ve talked about it, but like, we don’t have one system that’s like, this is the system that we use for everybody. But using some examples of how meal timing can impact your caloric intake. If you are somebody who is constantly grazing across the day, you’re probably likely to end up consuming more calories overall than if you are someone who is having like their three structured meals and their one to two structured snacks. So yeah, you’re constantly grazing, you are likely to eat more.
On the flip side, while almost all research on intermittent fasting has found people lose weight with that particular approach, there’s like the classic example of someone like missing breakfast and then being starving later in the day and then either bingeing or overeating, choosing less appropriate options that leads to a higher calorie intake. So it’s like, even though we see this in the research, it’s like, it’s not the same for everyone, which just highlights the need for an individual approach regardless. Overall, some attention should be paid to things like your eating window and your meal frequency, but unfortunately there’s no one size fits all approach and a lot of the time it comes down to trialing different ways of doing it and seeing what works for you.
Aidan:
Outside the fat loss side of things, like research on animals has consistently found that extended windows, of eating can be a potential issue for longevity. There’s not much reason that I’ve seen of it. I don’t know if you’ve seen of anything to make us think that that matters in humans. Yeah, but it’s actually interesting. That’s like almost every animal that has been studied like this actually seems to be something that’s relevant.
I wouldn’t read too much into that because as we said, we haven’t seen anything on humans that makes us think that. I’m also like, I also wouldn’t take it to an extreme. Like I don’t see many reasons why it would make sense to have a greater than 14 hour eating window. Like you could have a tiny bit of like waiting a little bit after you wake up and or waiting a little bit before you go to bed. Like realistically, firstly, if you’re getting eight hours of sleep a night, that’s only stopping before like two hours before you go to bed assuming you ate the second you woke up as well.
Where this does start to apply though is from the fat loss perspective is it’s super easy to fall into that 14 plus hour eating window under certain circumstances. For example, if somebody gets up really early, now that I’m in my running era, for example, people wake up at like 4.30 to go for a long run and stuff like that. It’s like they’ll have like pre-workout carbs or whatever before they go.
But then if they have dinner at the exact same time as everybody else and then they eat after dinner or whatever, like you obviously end up in a situation where it’s like you have just grazed for 16 hours in the day kind of thing. And if you were unintentionally over consuming calories, it’s like, well, that’s also unsurprising considering you’re eating like throughout the whole day basically.
Leah:
Yeah, from a practical point of view, I definitely see people that get up really early and exercise earlier in the morning struggling more with the appetite management stuff, because they’ve just got this huge window of eating. It’s like, it is hard to calorie control within that huge window and like keep appetite managed.
Aidan:
So now we’re going to talk about something that I don’t say perplex me, but I found interesting when I was going like very early in my career looking at all this stuff, but like, why does the research look so mixed? So the story I tell and I’ve probably told on this podcast is that there is a research review that I subscribe to and every month like there was, cause I was binge reading it. Like there was like every month, like the author Alan Aragon, like he would go through and review the most important nutrition studies that came out.
It seemed like this like phase where like every month he was reviewing a study on the effect of breakfast on fat loss. And it was like every second month it would come out showing like breakfast seems to matter and every or it doesn’t seem to matter. And there’s something something I had a lot of respect for is like the patience that he had in unpacking the study, treating each day as an individual study and treating that with the respect that it deserves. Then also after that zooming out and putting that in the context of the whole body of literature.
But let’s talk about why it seems to be a little bit mixed if you just looked at individual studies rather than zooming out. So the main one is the practical side of things. If we looked at research on skipping breakfast, for example, there could be two options, calories could be matched or calories might not be matched. If the calories are matched, that gives us more relevant information about being like, does this actually matter? Does the breakfast itself matter? Or is it about total intake? If the calories are not matched and it’s ad libertum, that makes it more applicable to real life.
But what if somebody just ate more or less calories because they had breakfast and had nothing to do with the breakfast itself, had everything to do with the total intake. So like that’s one of the other things. The next thing is like small sample sizes. It’s very hard to recruit a massive sample size for a randomised control trial. It’s just very hard to do. So a lot of research has small sample sizes that can skew things. Sometimes just random chance can occur. There’s a lot of things that can go on. And another thing that I’ve thought about a lot is it’s very bold to assume that calories are set up perfectly in studies.
There’s a few different angles that can be taken here in terms of study design. Sometimes research gives all the participants the same calories. And most people taking a second to think about that would be like, everybody has different needs. Like if you gave some people the same calories, like that could be a big deficit for somebody, that could be a surplus for somebody else. Like that’s not gonna work.
But the next step is like, they often try to individualise it. They might do a lead in period where they eat a certain amount of calories and they try to figure out people’s maintenance. They might use formulas. They might use a resting metabolic rate testing machine. There’s so many things, but it’s bold to assume that in all of these studies that we’re reading, that they’re giving the perfect amount of calories. And sometimes when you see like odd results, like that is literally just the explanation. It’s as simple as that. But you can see why those kind of differences exist because it’s very hard once again to get a good sample size and then just now every single variable.
Leah:
Absolutely a complex thing to research. So always appreciating the researchers out there trying to give us this information.
Aidan:
I always say, I don’t know if you see this, but like, cause obviously follow a lot of evidence-based practitioners, like these researchers will like post these training studies that like just like something to do with like lifting weights. Like they might be looking at like the effect on like training at long muscle lengths or whatever. There will always be people in the comments being like, you should have set it up this way. And it’s like, these people spent like six months on this study.
Leah:
They did think about it.
Aidan:
And it’s like, you can’t cover every single variable in every single study. It’s just impossible. Yeah, 100%. Overall, answering the question, does meal timing affect fat loss? From a practical perspective, there is definitely a lot to consider. But overall, there’s not this like, yeah one approach that’s gonna fit everyone that you should definitely intermittent fast or you should definitely have breakfast or it’s just not that it’s a lot more nuanced than that. And it’s gonna take some playing around and an individualised approach but it’s something that is worth considering.
So this has been episode 153 of the Ideal Nutrition Podcast. We’re gonna have another little plug this episode of a different podcast. So last episode, I plugged my podcast this episode, I’m gonna plug our new podcast, which is Insights with Ideal Nutrition, which is hosted by our coworker and colleague, Hannah Mills. And she essentially is interviewing nutrition professionals in different nutrition spaces and getting a little bit deeper insight into different aspects of nutrition and lifestyle. So if that’s something you want to check out, I highly recommend.