Aidan:
Hello and welcome to the Ideal Nutrition Podcast. My name is Aidan Mui, and I’m here with my co-host, Leah Higl. And this is episode 107 where we are going to be talking about why your calorie intake changes your calorie expenditure.
Leah:
Giving a little bit of a brief overview and background here, let’s talk about the components of energy expenditure itself. So we’ve got a few things that fall under this category. We’ve got our RMR, which is our resting metabolic rate, so basically our metabolism. So this is our calories burnt just at rest, so everything that our body does just at rest just to keep things going. And then we’ve also got the thermic effect of food, so that’s calories burnt digesting food. So whenever we eat food, it has a thermogenic effect where it does actually burn energy as well.
And then we’ve got non-exercise activity thermogenesis or NEAT for short, and that is just any incidental movements, so that’s things like just generally walking around, doing the housework, just general movement throughout the day that isn’t necessarily planned or voluntary exercise. And then on top of that, we do have our planned exercise, so that is exercise, activity, thermogenesis or EAT, but that’s just anything that is a planned voluntary exercise will fall under that. So those are the main components of energy expenditure. And our calorie intake can actually indirectly and directly affect all of those categories.
Aidan:
We’re going to break down each of those four categories and go a bit in depth on each of them. But I would just start with something that I personally find interesting just to show how this can play a pretty large role. So there’s a study where they got people to eat. It was 12 sets of twins, and they were over fed by a thousand calories per day, six days a week for a total of 84 days during a 100-day period, where on that 100th day, they ate maintenance calories. It’s a bit of a weird design. I don’t actually know why they did that.
But the moral of the story is that they overate by a thousand calories for call it just like 84 days basically. Physical activity was controlled in this study, which I think makes it more interesting because in the real world, if you overfed people by that much, maybe they change what they do physical activity wise. In this case, they were limited or I don’t want to say limited, but they had to do a 30-minute walk each day. They couldn’t do more. They couldn’t do less. That was all the planned physical activity that they could do. And in this study, there was a wild outcome. Somebody gained as little as 4.3 kilos and somebody else gained as much as 13.3 kilos.
Leah:
Huge discrepancy.
Aidan:
Huge discrepancy. It was relatively well controlled in that they had a lead in period to figure out their maintenance calories as well. So although you could be like, oh, maybe they didn’t get the maths absolutely perfect, it’s clear that they got it good enough that you can be like there was some significant changes in energy expenditure. This is one of the cases that some people look at this, I’ve posted this on Instagram a few times, and every now and then, people have tagged, big nutrition people, almost as if I’m saying that calories in versus calories out isn’t a thing.
I’m like, that’s not what I’m saying. I’m just saying the calories in portion changes the calories out as well. And doing some maths on this, you could actually look at this and be like, okay, the person who had a 13.3-kilo increase in body mass over this timeframe, their energy expenditure barely changed. If we actually do the mathematics on it based on how many calories go into a kilo of body fat and everything like that, their energy expenditure barely changed. Whereas the person who only gained 4.3 kilos had a huge increase in energy expenditure. Using slightly different wording, we call it a 1,000 calories surplus when somebody eats 1,000 calories over maintenance. But if your energy expenditure increased by 700 calories, is it still a 1,000 calorie surplus?
Leah:
It’s just the surplus on the initial maintenance calories. Yeah.
Aidan:
Yeah. I’ve never seen anyone else word it this way, but I’m sure people do. The wording I use is I would call that a net surplus of 300 at the end of the day. 1,000 calorie surplus, 700 calorie increase in energy expenditure, there’s 300 leftover, I’d call it a net 300 calorie surplus. It gets into semantics at that stage. But basically, what I’m saying is if you increase calorie intake, calorie expenditure often increases alongside that. But there’s some outliers like using that 13.3 kilo example, that person, it doesn’t fully make sense in a lot of ways when we talk through all these other things, but that person’s energy expenditure just didn’t increase.
Leah:
Yeah. I think going through this bit by bit and just talking about how our calorie intake can affect our calorie expenditure, a good place to start is looking at the general impacts on our basal metabolic rate or our resting metabolic rate. So like I said, your resting metabolic rate is just the calories you burn at rest, so your baseline metabolism. Changes in body size firstly will change how many calories you burn at rest. So larger bodies will burn more calories at rest, obviously, than smaller bodies where there’s less muscle fat and other things to maintain. So if you have an increased caloric intake and this results in an increase in weight, this alone will increase your basal metabolic rate; and vice versa, if you’re losing weight, you’ll have this decrease in basal metabolic rate. So that’s just from the effect of changes in body size.
But we also know that your calorie intake does directly affect or can directly affect your calorie expenditure through the process of metabolic adaptation. So when you increase your caloric intake, your baseline metabolism will also increase. Sometimes this will be a little bit, sometimes it might be more, but also if you decrease your caloric intake, your RMR, your BMR will slightly decrease with it. So we know that metabolism isn’t this static thing. There are lots of things that affect it, but our calorie intake and what we do over that longer term with our caloric intake does directly affect how much we actually burn at base.
In terms of I guess examples of how this actually takes place in the body, I think looking at when you go into a caloric deficit and we see this downregulation in metabolism, I like thinking about, well, what is this actually coming from? What does this in the body? What do we down regulate? So examples of this would be a decreased heart rate and burning less calories through that. That’d also potentially be downregulation of other functions like digestion and immunity as well. We also see fewer calories being used in the process of muscle growth when we’re in a caloric deficit. And then in more severe cases where there’s quite a large calorie deficit or a prolonged deficit, we can also see loss of a regular menstrual cycle or HA in some people, so that is the process of our body shutting down menstruation just to conserve calories.
So there’s a lot of ways our body can down regulate things to conserve calories when we are in a calorie deficit. Vice versa, when we are in a calorie surplus or an increased caloric intake, our body up regulates some of these processes.
Aidan:
The definition of metabolic adaptation is something along the lines of the decrease in resting metabolic rate. That is more than you would expect based on what a formula would predict. A formula would predict just the changes in body mass, which we talked about. The changes in body mass will result in change, but metabolic adaptation is anything more than that. And there’s two separate definitions of metabolic adaptation. One is just looking at resting metabolic rate, which is usually not a huge factor in all of this, but it is something that can change a little bit. And the other broader one will cover all these other changes, but in particular, changes in physical activity, which we’ll talk about as well.
The simplest one for us to understand though is the thermic effect of food. This is something that arguably changes almost instantly when you change your calorie intake. So the thermic effect of food is the calories your body burns in the process of digesting, absorbing and metabolizing foods. The reason why this is such an easy one for us to get our heads around is because typically, the thermic effect of food makes up around 10% of your calorie intake. That is a very average type of number. And what I mean by that is if somebody ate higher protein, higher fiber, they would have a higher thermic effect of food. Maybe it gets as high as 15. If somebody had a very processed food intake, low protein and low fiber, maybe it gets as low as say 5%.
But using the example, if somebody was to be eating 2,000 calories per day, the thermic effect of food could be around 200 calories. If they increase their calorie intake up to 3,000 and they kept eating the exact same type of foods, suddenly it could now be 300 calories that are burned through the thermic effect of food. That’s easy to get our heads around. If you eat more food, you burn more calories in the process of eating and digesting food. If you eat less, you burn less through that process.
Leah:
Another place where calorie intake can impact our resting metabolic rate is through the effects on incidental movement as well. So that goes back to our NEAT, so non-exercise activity thermogenesis. I actually hate those acronyms so much so I just call it incidental movement because it’s anything that we do movement wise that isn’t planned exercise. But there’s a couple of ways that this can impact. So firstly, going back to the body weight stuff. So we do know that when we reduce our caloric intake, there’s a reduction in body weight. This means that there’s probably a reduced calories burnt through things like your daily steps and general movement, and then vice versa with an increase in body weight.
But then, we also have the impacts on our subconscious movement. So for example, increases in calories usually result in increases in incidental movement. That would make sense. When you have more calories available, you’re probably going to feel more energetic. You’re probably going to choose to walk to the shops. There’s just things you’ll do subconsciously, whether it’s fidgeting, whether it is slightly more a conscious effort, but you’ll just have more energy to do things. We see this increase in incidental movement when there are more calories available. And then again, vice versa, with a decrease in caloric intake, less energy available so maybe you’re less likely to do these kinds of daily movement.
I love the example that you bring up often about bodybuilders in competition prep. Obviously, this is quite a severe case when you’re like, that’s not everybody, but I think it really highlights this change in incidental movement quite well. But we do notice that bodybuilders in competition prep seem to just move less in just general speaking so in how animated they are when they are speaking, they tend to talk slower, even blink slower, everything is slower.
Their body is just trying to conserve as much energy as possible because they just do not have a lot of it. I think that is just a really good example of highlighting this. Vice versa, when they have a nice big calorie surplus, they’re probably the complete opposite and maybe more jittery and fidgety and their body is doing things to burn this excess calorie intake.
Aidan:
Yeah. It’s wild because if you follow a lot of people on social media who are influencers, etc. and they do a lot of video content, you’ll see this if they do compete in bodybuilding where it’s like when they’re six-plus months away from a show, they can be really animated and stuff like that. And as it gets slower, it’s like they’re no longer moving around as much in the videos. They’re standing still, talking to a camera, barely blinking. You actually can see this.
Leah:
It’s crazy. My partner used to do bodybuilding and he would even say that he would stop just using pleasantries and talking to conserve energy so there was no please or thank you. He’d just caveman mode his language because that’s how little energy he had coming in. Yeah, it’s crazy.
Aidan:
Yeah, and it’s part of why a lot of bodybuilding coaches do step counts because obviously, doing more steps does increase energy expansion, it makes it easier to get lean, but it also is a way of keeping that variable a little bit more constant because if somebody was just naturally going about their day, walking as much as they want to walk or anything like that in the off season, and then they didn’t have a step count and they got through competition prep naturally, that would often drop off. So by keeping a step count, at least … It doesn’t solve this problem, but it can keep that variable a little bit more consistent.
The other, I don’t know how I feel about this example but I do think it’s worthwhile thinking about, the other example that’s relevant is Parkinson’s. So it’s not really on the same topic, but bear with me for a second. With Parkinson’s disease, people have unintended shaking their hands and stuff like that would be shaking and their calorie requirements are significantly higher than the average person. It can create two challenges. One, because it can make it harder to eat, but two, their energy expansion is higher, so a lot of people do lose a lot of weight unintentionally with Parkinson’s disease, and that’s a challenge that we have to try to overcome where possible. But it’s an example of how if somebody was just naturally just fidgeting all the time, their calorie expansion would be higher.
Now onto the more intentional exercise type of stuff. So the easy one to get our head around is that reductions in body weight obviously equals reduced calories burned through exercise if all other factors remained equal. If somebody was a hundred kilos and they went out for a, I don’t know, let’s say a walk, like an intentional walk, and they walked three K’s. And over time, they lost 20 kilos but they continued walking three K’s. The hundred-kilo person would be burning more calories than they would when they were 80 kilos basically. So that adds up. Same thing with running, playing sport, even just moving around, lifting all of those things, unless you’re obviously progressively overloading, which would add on to this.
But there is another argument that exercise becomes more efficient when on lower calories. I wouldn’t focus on that too much since it’s likely a smaller factor than all the other variables, but it is a factor that has been studied. I was even listening to Eric Trexler talk about metabolic adaptation earlier today, and he’s going through all the variables about why metabolic adaptation is so complex, little details about how it’s so hard to measure how much of all of these variables are explaining the changes and everything like that. But he was talking about this study, which I obviously haven’t read, I was just listening to a podcast earlier today, but he was talking about how they were getting people onto, I don’t know, just cycling so on a bike in the gym.
And as they lost weight, they were becoming more efficient and they were burning less calories while cycling. They were measuring their calorie expenditure. And one of the things that they were doing was they were even adding little leg weights onto their feet to keep their leg mass the same while cycling to control for that variable. And they still were burning slightly less calories as they became a little bit more efficient. So it’s another variable as well.
Leah:
There are honestly so many ways in which our calorie intake can either directly or indirectly in some way impact our calorie expenditure. It’s definitely a complicated topic, but I think it’s an important thing to just be aware of, especially when I guess looking at your calories in versus calories out, and like you said, talking about certain aspects of this like that study. Obviously, it still comes down to calories in versus calories out, but what we do with our calorie intake can impact our expenditure so much so these sides of the equation can impact one another. And it affects us whether we notice it or not. It’s important to note as well that some people experience it more than others. Obviously, in that study, some people saw a greater caloric expenditure versus others, even though the baseline surplus was the same.
Aidan:
Yeah. And I want to jump in on that because now that we’ve gone through all these variables, you can see how absurd it was that one person’s energy expenditure didn’t change. Starting with the most obvious one, the thermic effect of food. If you added a thousand calories, your thermic effect of food should increase by about a hundred, maybe 50, maybe 150, maybe 200, but it should increase. And that makes that tough to explain in terms of being like how did his energy expansion not really increase? When you look at it, I think the easiest way for me to wrap my head around it is that these variables aren’t always perfectly precisely measured. Sometimes we do just burn more calories randomly because we have a day where we fidget more, sometimes we move slightly more or less, etc.
And it’s like maybe during the baseline period, maybe the researchers got his maintenance calories slightly wrong or maybe … I mean by a very small margin but slightly wrong. Or maybe he did just move a little bit more during that and there was some small increases that happened during this phase, but there were other small decreases that also happened during the phase, which offset it. So there wasn’t much of a difference. But yeah, it’s really fascinating that even no matter how you go about explaining it, it’s very clear that that person was an outlier in comparison to the other people because his energy expansion didn’t change as much as the other people. Super interesting but obviously super complex.
Leah:
Super, super complex for sure.
Aidan:
So I wanted to go through a few more things about how does this fit into other models we have about thinking about nutrition training, etc. So a very popular approach is reverse dieting. We’ve spoken about this on the podcast. And when you understand how energy expenditure is changed by calorie intake, it also makes it easy to understand how reverse dieting works. So for anybody who isn’t familiar with this, just very quickly going through it, reverse dieting is the concept of, say you finish a calorie deficit, you get as lean as you wanted to in that phase, you slowly add calories back in. Say you add a hundred calories per day as each week goes by. Something that a lot of coaches will talk about, they’ll be like, “Oh, this person was in a 500-calorie deficit. We added a hundred calories per day each week for 10 weeks before they started gaining weight again, which therefore means we’ve built up their metabolic rate because they were in a 500-calorie deficit, but took a thousand calorie gain before they got back to maintenance calories.”
And there’s a few things that are going on with that obviously. One of them is that their metabolic adaptation could reverse. That could explain a few hundred calories change. A second one that may or may not be relevant, but obviously we’d never know for sure how many calories somebody is on. We don’t know adherence, all those things. Adherence often improves as we start aiming for higher calories. There’s a few other just angles of looking at that from, I think. Is there anything you want to add on the reverse dieting side of things?
Leah:
I think just that noting that maintenance calories is an ever-changing target. So whatever your baseline maintenance calories are in a surplus, in a deficit, that’s going to change as you change your calorie intake. I think a lot of people see it as this is my maintenance calories instead of it being this changing target.
Aidan:
Yeah, for sure. There was a few other things I was going to touch on that I was blanking on. So one of them is basically that as you increase your calorie intake and you reverse dieting, by the time you start noticing weight gain, you might have actually been in a surplus for a few weeks before that actually occurred. So it’s like maybe they were in a 300 or 400-calorie surplus by the time they noticed that. So it hasn’t actually moved maintenance that much.
And then the final concept, the most important one I really wanted to get at is reverse dieting can have a place, but it’s also not magical because how would reverse dieting increase your metabolic rate any quicker than just jumping straight back to maintenance calories? Because if you start reverse dieting while in, say, a 500-calorie deficit and it takes at least five weeks to get back to wherever your maintenance would have been, you’re still spending more time in a deficit, which is prolonging all of these things.
Leah:
It’s a slower way of doing the same thing.
Aidan:
Yeah. Whereas you could jump back up that 500 calories to start off with and then see if you can increase a little bit more as these things reverse.
The other concept to very, very briefly touch on is the concept of building up your metabolism prior to a fat loss phase. When people learn about metabolic adaptation, they often go, okay, let’s say I do that full reverse dieting approach and everything like that or something along those lines, spend time on higher calories that should set me up for a high fat loss phase. And to be honest, I do think that is a good idea for many, many reasons. But from the metabolic adaptation side of things, it probably matters a lot less than a lot of people would think. And the reason for that is because metabolic adaptation happens quickly. It can go in both directions.
A lot of research that we’ve spoken about a fair bit as well is that if you spend say four weeks at maintenance calories after a calorie deficit, we can barely measure metabolic adaptation anymore because if you go through all these variables, we talked about the thermic effect food, as I said, that happens almost instantly. The effects on incidental movement once again after about four weeks is probably if you’re at maintenance calories, that goes back to the baseline. That efficiency with exercise, I don’t think that would take very long to get back to normal. And then the metabolism stuff that we spoke about is not really a large variable to start off with. So if you spent, let’s say months building up your metabolism and then you went to a deficit, it’s very likely that within say four weeks, you’ve got all of that work that you’ve done is back to square one in terms of the metabolic stuff.
Leah:
Yeah, it’s not like it’s going to have a huge lasting effect throughout months and months of a calorie deficit. So I think that is a good summary. Anything else to add there?
Aidan:
I would just say if you were going to do that, you’d do it for other reasons like spending time focusing on building muscle, building a better relationship with food, spending time just on higher calories and fueling training.
Leah:
Just building a good baseline of nutrition.
Aidan:
Yeah. I think it matters a lot for a lot of other reasons.
Leah:
This has been episode 107 of the Ideal Nutrition Podcast. If you haven’t yet left a rating or review, it’s always greatly appreciated that you could maybe do so because we love getting some good, positive reviews in there, but otherwise, thanks for tuning in.