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Most people tend to view exercise through the lens of the ‘additive’ energy model: More exercise = more calories burned.
But back in 2016, Herman Pontzer and colleagues published a study that put forth the ‘constrained’ energy model: Energy expenditure does increase with added activity, but only to a point. 1
In other words, if you go from being sedentary to active, you’ll see an increase in energy expenditure. But if you’re already very active and increase physical activity levels further, you aren’t likely to see energy expenditure increase linearly because the body adjusts other processes to maintain total energy expenditure within a narrow range.
Additive model (left): the more activity you do, the more calories you burn. The constrained model (right): As levels of physical activity increase, the body adjusts other aspects of energy expenditure to maintain TDEE within a certain range
For example, a recent paper found weight loss was only half of what was expected in a group burning 2000-2500 kcals/wk. The researchers explained this was likely due to behavioural adaptations that reduced 24-hour energy expenditure. 2
At the time, this was an interesting finding that seemed to offer a tentative explanation for why people don’t always lose the expected amount of weight despite doing a bunch of physical activity.
Then, this area of research went pretty quiet, and there were questions about the validity of the constrained energy model. After all, it was just one study––did we jump the gun?
Well, two recent studies have added to the constrained energy model.
In the first, Careau and colleagues looked at total energy expenditure in 1,754 adults living normal lives and found energy compensation averaged 28%.
In other words, if someone increased their physical activity levels by 500 kcals, you’d assume this would mean their total energy expenditure also increased by 500 kcals. However, according to this study, the actual increase in energy expenditure would only be 360 kcals. 3
But the researchers also found something else: Leaner individuals compensated less (29.7% compensation) than individuals with more body fat (45.7% compensation).
As the researchers explain:
Not just because the amount of exercise required to achieve this is impossible for most people, especially when you’re not paying attention to how much you eat, but because the number of calories you think you burned during exercise isn’t how many calories you really burned due to the compensation that takes place. This compensation seems to increase as fat mass increases.
The goal of training during a fat loss phase is to maintain muscle and strength. If you enjoy cardio, do it for the health benefits, not to burn more calories. Of course, cardio can be implemented to increase the deficit, but be mindful of how much you’re doing so you don’t inadvertently end up in too big a deficit, which then increases fatigue, and results in less movement the rest of the day.
2- Your energy balance status likely impacts the degree of compensation
If you’re at maintenance or a surplus, you could probably get away with a bit more physical activity without experiencing the same degree of compensation you would during a deficit.
This also adds to the point above: If you do more exercise in the hopes you’ll ‘speed’ up fat loss, the more likely the compensation is to kick in. Hence why the goal of a fat loss diet is to coax (not force) fat loss.
3- Stop paying attention to your smartwatch.
While this point isn’t directly related to the topic, I think it’s still worth mentioning. Or, well, mentioning again because I still get questions from people on whether or not they should ‘eat back’ their exercise calories.
Let’s forget that smartwatches are terrible at accurately estimating energy expenditure (see this and this). And even if they were accurate, they wouldn’t be able to account for the compensation that occurs.
That said, smartwatches seem pretty accurate for tracking step counts, and you can use this to your advantage. If you know how many steps you’re doing at the start of a diet, you can try to maintain the number of steps throughout the diet to help keep energy expenditure up.
But that isn’t what the constrained energy model suggests. As I mentioned above, the constrained energy model states that physical activity does increase energy expenditure, but only up to a point. It’s when physical activity becomes excessive that the increase in energy expenditure plateaus.
Putting aside all of the obvious benefits of exercise, one of the biggest benefits of regular exercise is its role in weight maintenance. In fact, according to the latest systematic review on the subject, it’s the “most consistent positive correlate of weight loss maintenance.” 5
So exercise is definitely important. And contrary to what a lot of people say, exercise will increase your energy expenditure, just not as much as you’d want it to, and the extent to which it does will decrease, and eventually plateau, as you reach higher levels of activity.
It’s time we shift the focus away from using exercise as a way to burn calories and put more emphasis on using physical activity as a way to improve our health and support our fitness goals. Any increase in energy expenditure should be seen as a nice add-on, not the sole reason for exercising.
But back in 2016, Herman Pontzer and colleagues published a study that put forth the ‘constrained’ energy model: Energy expenditure does increase with added activity, but only to a point. 1
In other words, if you go from being sedentary to active, you’ll see an increase in energy expenditure. But if you’re already very active and increase physical activity levels further, you aren’t likely to see energy expenditure increase linearly because the body adjusts other processes to maintain total energy expenditure within a narrow range.
Additive model (left): the more activity you do, the more calories you burn. The constrained model (right): As levels of physical activity increase, the body adjusts other aspects of energy expenditure to maintain TDEE within a certain rangeFor example, a recent paper found weight loss was only half of what was expected in a group burning 2000-2500 kcals/wk. The researchers explained this was likely due to behavioural adaptations that reduced 24-hour energy expenditure. 2
At the time, this was an interesting finding that seemed to offer a tentative explanation for why people don’t always lose the expected amount of weight despite doing a bunch of physical activity.
Then, this area of research went pretty quiet, and there were questions about the validity of the constrained energy model. After all, it was just one study––did we jump the gun?
Well, two recent studies have added to the constrained energy model.
In the first, Careau and colleagues looked at total energy expenditure in 1,754 adults living normal lives and found energy compensation averaged 28%.
In other words, if someone increased their physical activity levels by 500 kcals, you’d assume this would mean their total energy expenditure also increased by 500 kcals. However, according to this study, the actual increase in energy expenditure would only be 360 kcals. 3
But the researchers also found something else: Leaner individuals compensated less (29.7% compensation) than individuals with more body fat (45.7% compensation).
As the researchers explain:
In the second study published earlier this year, researchers found energy balance influenced total energy expenditure such that when participants were at maintenance or a surplus, the additive model held true (to a point), whereas when participants were in a deficit, the constrained model held true. 4
Now, there’s a lot to unpack here. But a few key points we can take away from all of this.
1- Trying to ‘out-train’ your diet is a losing strategyNot just because the amount of exercise required to achieve this is impossible for most people, especially when you’re not paying attention to how much you eat, but because the number of calories you think you burned during exercise isn’t how many calories you really burned due to the compensation that takes place. This compensation seems to increase as fat mass increases.
The goal of training during a fat loss phase is to maintain muscle and strength. If you enjoy cardio, do it for the health benefits, not to burn more calories. Of course, cardio can be implemented to increase the deficit, but be mindful of how much you’re doing so you don’t inadvertently end up in too big a deficit, which then increases fatigue, and results in less movement the rest of the day.
2- Your energy balance status likely impacts the degree of compensation
If you’re at maintenance or a surplus, you could probably get away with a bit more physical activity without experiencing the same degree of compensation you would during a deficit.
This also adds to the point above: If you do more exercise in the hopes you’ll ‘speed’ up fat loss, the more likely the compensation is to kick in. Hence why the goal of a fat loss diet is to coax (not force) fat loss.
3- Stop paying attention to your smartwatch.
While this point isn’t directly related to the topic, I think it’s still worth mentioning. Or, well, mentioning again because I still get questions from people on whether or not they should ‘eat back’ their exercise calories.
Let’s forget that smartwatches are terrible at accurately estimating energy expenditure (see this and this). And even if they were accurate, they wouldn’t be able to account for the compensation that occurs.
That said, smartwatches seem pretty accurate for tracking step counts, and you can use this to your advantage. If you know how many steps you’re doing at the start of a diet, you can try to maintain the number of steps throughout the diet to help keep energy expenditure up.
Finally, before wrapping up, I want to emphasise that physical activity is important.
I’ve seen many people misinterpret the original Pontzer study to imply that physical activity is pointless.But that isn’t what the constrained energy model suggests. As I mentioned above, the constrained energy model states that physical activity does increase energy expenditure, but only up to a point. It’s when physical activity becomes excessive that the increase in energy expenditure plateaus.
Putting aside all of the obvious benefits of exercise, one of the biggest benefits of regular exercise is its role in weight maintenance. In fact, according to the latest systematic review on the subject, it’s the “most consistent positive correlate of weight loss maintenance.” 5
So exercise is definitely important. And contrary to what a lot of people say, exercise will increase your energy expenditure, just not as much as you’d want it to, and the extent to which it does will decrease, and eventually plateau, as you reach higher levels of activity.
It’s time we shift the focus away from using exercise as a way to burn calories and put more emphasis on using physical activity as a way to improve our health and support our fitness goals. Any increase in energy expenditure should be seen as a nice add-on, not the sole reason for exercising.
