Aidan:

Hello and welcome to episode 172 of the Ideal Nutrition Podcast. My name is Aidan Muir and I’m here with my co-host, Leah Higl and today we’re going to be talking about how differently do people respond to the same size calorie surplus/ deficit. So this partly stems from the fact that if somebody is in a calorie surplus consistently, they’re going to be gaining size over time. If somebody’s in a calorie deficit consistently, they’re going to be losing size over time.

That’s true. That’s just kind of factual information outside of like exceptions. Say if somebody was losing two or three kilos of tissue in the form of muscle and fat, and then they drank three and a half liters of water, like obviously, but like that’s why I say over time, right? Anyway, that’s true for everybody. Where things get a little bit individual though is how people respond to the same size thing. So going super basic, I’m going to talk about the whole like 7,700 calorie rule thing for a second.

I’ve talked about it before, but there’s 7, 700 calories in a kilo of body fat and around 1,200 calories in a kilo of muscle, but it’s energetically expensive to build muscle. I often say it takes around five times that number, but we don’t have specific numbers. It could be less than that, but it takes more than 1,c200 to build a kilo of muscle. Whereas body fat gets stored far more easily. There’s just 7,700 calories there. You could therefore oversimplified do some math and be like, okay, if 500 calorie deficit per day should theoretically result in half a kilo of fat loss per week based off of that maths. It’s a solid-ish type of rule to give you a bit of a baseline of understanding. But there are so many reasons why that won’t be accurate, because energy expenditure will change in response to changes in energy intake. And plus, there’s a lot of individual variation, which is what we’re going to explore today.

Leah:

We’re going to start by unpacking the theory, and then we’re going to move into more so research-based stuff. But when you change your habitual energy, calorie intake, there are going to be inherent changes to your calorie output. And this can actually be through several mechanisms. So it can get quite complex. So firstly, we do have our BMR, so our basal metabolic rate. And this is just how many calories we burn at rest on a day-to-day basis through our quote-on-quote metabolism. And this is going to adapt in accordance with our habitual calorie consumption.

You may have heard us talk about this previously in regards to metabolic adaptation, where when we increase food calorie intake, there is kind of this up regulation of certain bodily functions that then goes on to burn more calories. And then on the flip side, when calories are reduced habitually, we see this reduced calorie output through a down regulation. So it’s like this constantly somewhat moving target in terms of our basal metabolic rate. So it kind of adapts to what we are putting in on a habitual basis. How much your intake changes your total basal metabolic rate will depend on a few things. The first thing being the size of the surplus or deficit, the length of that particular phase, but also we know genetics can play a fair bit of a role here.

Aidan:

So talking through how there’s other changes in intake that can lead to changes in age expenditure directly, you’ve touched on like basal metabolic rate with metabolic adaptation. The next one I’ll go through is the thermic effect of food. So when we eat food, takes calories to eat and digest food as well and we call that the thermic effect of food. I often call it about 10%, although it’s obviously variable. If you had higher protein, higher fibre, unprocessed food, it typically goes higher than that, maybe 15%.

If you went significantly lower than that in terms of low protein, low fibre, very processed food, maybe just as low as 5%. But using that logic, if say somebody went into that mouse I talked about before, like a 500 calorie surplus per day, if we use the 10 % rule, then like, well, 50 calories suddenly goes missing through the thermic effect of food instantly. So your intake obviously changes your expenditure based on just that, as well as all the other stuff we’re talking about.

Leah:

We also have our neat, which can potentially change. So this is more our like, incidental movement, so non-exercise activity thermogenesis. So for someone who is in a caloric surplus or where we’ve increased calorie consumption, we might find that we just have more energy, so we’re just more energetic, and this could lead to more incidental movement. Even things like fidgeting can play a big role here. And then on the flip side again, we have when we go into a caloric deficit and cut calories, we potentially experience being less energetic and therefore have less incidental movement in our day to day lives. Whether that’s kind of just moving around a little less or whether it is less fidgeting, of all these things fit into here. But there could be quite a shift in how much you are burning through your neat.

Aidan:

And then talking about formal exercise, you could have changes there. It’s probably less relevant than the other stuff that we’ve talked about. Maybe you want to train less, like maybe you do less actual formal exercise. Another thing that’s been proposed is sometimes people start exercising more efficiently is they might burn less calories for the same movement potentially. And very big picture as well, obviously less relevant than today. This is not so individual, but like if somebody lost say 10 kilos and did the exact same exercise, they’re going to be burning less calories through that exact same exercise. That’s not too relevant to say, but it’s just another point about how intake obviously changes the expenditure over time as well.

Now we’re going to talk through other theoretical stuff that’s not as direct as that. So one is that the absorption of food can change as well. This plays a little role. The example I always use is research looking at almonds basically found that people typically absorb 70 to 80% of the calories from almonds. And that is not talking about the thermic effect of food. That’s literal absorption of those calories. If we were consuming sugar, it’s probably much closer to 100%.

This probably also scales based on your intake of food. Like I would make a small wager that if you had a lower intake, you’re probably absorbing a larger percentage than if you had a larger intake. Probably no big deal, but it’s just a small factor. Other stuff that can change. And like I supposed to be clear, this is also coming back to individual variation as well. Just being like some people will absorb more than others, which is the key point I’m getting at there too. Another thing is difference based on muscle fat versus gain, fat gain. So muscle versus fat gain and the different caloric values.

Like if we’re looking at how people respond to the same size calorie surplus, what if one person was gaining a lot of body fat, not much muscle, and somebody else is gaining a lot of muscle and not much fat. If one is 7,700 calories per kilo and the other is 1,200, even though it’s a little bit more energetically expensive and everything like that, it’ll still come out less than 7,700. So that will change how much we’re affected here. The crazy thing, food for thought, this matters way more in the deficit. In a surplus, you know how it says energetically expensive?

It’s not energetically expensive to lose in a deficit. Low key, if you’re losing muscle in a deficit, you can lose more total body weight because if a kilo of muscle is only made up of 1200 calories, let’s say you do create a net over the course of a decent period of time, 7,000 calorie deficit. If you are only losing body fat, you might lose just around one kilo of body fat. If you’re losing muscle, it’s a much larger number. Food for thought with the individual variation. Some people hold on to muscle better than others.

Then other stuff that is very indirect here. Adherence to the plan can obviously change. Two people could be in the same size surplus or deficit and have different responses. That’s separate today’s podcast episode, but in the real world, that matters more than almost everything we’re talking about today, which is really another key variable too.

Leah:

So delving a little bit into the research, we’re going to start by using one single study as a bit of an example to highlight what we’re talking about here. So this is going to be linked in the show notes if you want to have a deeper look.

But the study itself had 24 participants, so not a huge study, but they basically overfed the participants for 84 days by 1000 calories per day. So technically it was a 100 day study, but there were, every seventh day was more, it was at maintenance. So not every single of those 100 days was an overfeeding day. They also did a maintenance phase leading into the study to confirm it was a 1000 calorie surplus. So they kind of individually assessed each person and then added the same size surplus to everybody as a way to standardise it. And then all exercise was also standardised to a 30 minute walk per day for all participants. And then the average gain there was 8.1 kilos over that 100 days.

But there was a bit of variation between how much each person had gained. So somebody gained as much as 13.3 kilos, while someone else only gained 4.3 kilos. So like pretty crazy range there with that average being 8.1. So assuming a decent level of compliance, we’ll probably come back to that, but assuming that, this study does highlight how differently each person may respond to a calorie surplus and potentially even then a deficit even if theoretically it is the same size surplus slash deficit.

Aidan:

13.3 versus 4.3 is such a huge difference. I’ve posted this study on Instagram before, I think I’ve talked about it on the podcast too, and like people tag like all of those, like the kind of like Layne Norton’s TNF on TikTok and Dr. Ids. Like there was a few people who just like tagged all three of them being like. Nah, this guy’s making this up. Like trying to dispute calories in calories out.

And like, it’s not, it’s just like, literally there is a difference in response to this, but the difference is due to the stuff that we talked about. It’s not like calories in, calories out don’t work. let’s look at that again for just half a second. Every single person gained size. Everybody was in a surplus and everybody gained size. The difference was how much they gained. And that is largely due to what was the net size of the surplus after accounting for things like absorption and changes in energy expenditure.

Let’s go a little deeper on this though. Like this might sound like a lot of maths. I think it’s interesting. I’m going to do it anyway. So for context, if you do the maths on it, theoretically, because it was 84 days at a 1000 calorie surplus, the combined total surplus, not net surplus, but total surplus was 84,000 calories. For context, if the 13.3 kilos was 100% body fat and nothing else, that would actually require over 100,000 calories due to the 7,700 calorie rule. So therefore we know that there’s a little discrepancy there by definition.

This therefore means that if the mass was perfect, that person must have had no increase in energy expenditure whatsoever and maybe even a small drop and then gained some weight in the form of non-fat. For example, muscle, which had a lower calorie thing as we talked about, glycogen, which technically is made up of calories, but there’s less calories in that. Food weight, water weight, et cetera, which is obviously very reasonable because it’s like you’re eating a 1000 calorie surplus, of course, you’re going to gain some weight, like a couple of kilos in the form of food, water, glycogen, if you that for a long period of time. But then the next little variable to chuck in is potentially the maths wasn’t perfect. Like I do feel like some people read these studies and like I know that they actually did this pretty well. Like they control a lot of variables, they do the maintenance studies.

And sometimes people just make the assumption that it’s like, that was exactly their maintenance calories. But it’s like, well, what if that person was already, what if the mouse came out a little bit skewed and they were already in a 200 calorie surplus at the start and it had just kind of presented itself as a, it looked like maintenance. Like there’s a little bit of margin for error, which therefore meant the actual surplus could have been larger. So that’s another thing to chuck in.

But then like, let’s look at the big key takeaway. I just thought that the 13.3 number is interesting when you factor in that stuff that was talked about, the person who only gained 4.4 kilo clearly had a huge increase in calorie expenditure and or decrease in calorie absorption. That’s the only way to kind of explain that with such a large surplus. Keep in mind that once again, maybe the math wasn’t perfect, maybe they were in a small deficit at start of it, but still 4.4 is so low that even a small discrepancy wouldn’t explain that.

Leah:

Yeah, and that is just one very small study. So it’s a very small sample size. It was just one study but it’s safe to say there was a huge variation in responses and particularly when factoring in other ways that we might respond to kind of a surplus or a deficit, like one person’s appetite might change more than another and therefore that could impact kind of general compliance to that surplus. So there are other things to consider there. Finding research on this topic is a bit harder than you would think. It would be lovely if we had like a bunch of these studies with way bigger sample sizes. But theoretically there is a lot of research out there since we can look at any controlled study that does have a surplus or deficit involved. It’s just hard to find compilations of useful data that we can actually kind of see these responses.

Aidan:

Yeah, that’s the tricky thing. Like theoretically, like literally any controlled data with a controlled surplus size, like we could use to talk about here. It’s just hard to find something like. It’s the narrative, well, it’s hard to find something that like has those clear discrepancies, which allows us to talk about all of those other things. And that whole thing I about with like the maintenance phase at the start, then leading to the surplus. So we know it’s roughly that size surplus. Like that data is rare. It takes a lot to find that. It does exist though, but it’s just hard to find.

So that brings you to obvious question. Like, does this all have to be research based? Like what about stuff in practice? And that’s another thing being like, we have heaps of research on that. We also have heaps of stuff in person like working with real people. I think there’s a lot of merit to paying attention to that with individual variation, particularly given like we work with a lot of people, not only us, we can look around like even just the ideal nutrition team, have 10 dietitians now, like we’re working with lot of people and then all the other dietitians, all the other coaches, all these other things. But although we have that stuff, I do think it’s almost borderline ignoring that data when it comes to assessing individual variation in terms of responses to surpluses and deficits.

For example, I have a bunch of clients who are on higher calories than you would predict that they would need to gain weight at a relatively slow rate. But it’s not like we’re there all the time. I take their word for it, but we’re not there. Like in this thing that we just kind of talked about, like all the food was provided, they were standardised for a 30 minute walk. These people that I’m working with, it’s like, I’m not even, I’m not there like making sure they do exactly 30 minutes walking, exactly the training, especially like this, just, there’s too much stuff that’s like, making the self-reported data unreliable, which once again, every time self-reported data is looked at, there’s evidence that it is unreliable.

If somebody seems like they’re an outlier, they could be an outlier, or maybe their reporting could be off, or maybe it could be a combination of both of them. We can still work very effectively with them and see really good progress working with them, but I’d be hesitant to report that data back in podcast format or something like that, just because that data is a little bit unreliable as well.

Leah:

Yeah, so there’s like, there is clearly a difference in how each individual responds kind of regardless of general reporting data. It’s like, we know that different people, even in practice, like I have clients that are very similar on paper who respond very differently to like a similar size deficit or surplus. Their bodies just respond differently. Maybe their appetite responds differently. So huge kind of range in response.

This doesn’t break the calories in versus calories out model. And I think that’s an important thing to highlight because all of this stuff is literally just built into the model. So rather than thinking about it in like that very simplistic form, this equation is actually highly complex with many moving parts and things that as soon as you change one variable, that could change another variable. And it’s like, it’s, it’s quite complex. So I think if you’re thinking about it simplistically, yeah, it could look like it breaks this model, but in reality, it does not.

Aidan:

This has been episode 172 of the Ideal Nutrition Podcast. If you have not already, please leave a rating and review if it is a 5 star one.