Comment by sdfhbdf
6 months ago
I've also been interested for some time in how metabolism works and wanted to debunk the popular myth for my friends that exercise burns a lot of calories, since I was under the impression that around 80% of energy we burn is just by "living" - breathing and thinking.
Reading this article I'm a little confused by the author's conflation of brain energy and the energy expenditure of the body as a whole. In the beginning they mention:
> "Your brain consumes roughly 20 to 25% of your body's total energy at rest"
while later they say:
> "Even chess grandmasters, who sit for hours in states of intense concentration, burn only about 1.67 calories per minute while playing, compared to 1.53 calories per minute at rest"
That second figure seems to refer to whole-body expenditure, not just the brain. And intense cognitive work doesn't happen in a metabolic vacuum - there's increased cerebral blood flow, elevated sympathetic nervous system activity, changes in heart rate variability, hormonal shifts (cortisol, adrenaline). These all have systemic metabolic costs that go beyond the glucose the neurons themselves consume. So the "it's just a banana and a half" framing might be undercounting by quietly switching between brain-only and whole-body measurements.
Also somewhat related - the link to businessinsider about chess grandmasters is broken, but another very interesting rabbit hole here is how energy expenditure is actually measured. A lot of what consumer devices and even many studies report is based on proxy biomarkers like heart rate, HRV, weight, age, and sex, run through linear regression models. True calorimetry (indirect via gas exchange, or direct in a metabolic chamber) is expensive and impractical outside lab settings. That means the precise calorie figures cited with such confidence - the "100 to 200 extra calories" from a day of thinking, or the per-minute burn rates of chess grandmasters - likely carry wider error bars than the article suggests. We don't really have a great way to measure real-world energy expenditure accurately at the individual level, which makes me a bit cautious about the neat narrative of "thinking is calorically cheap, full stop."
That said, the core point about adenosine accumulation and perceived exertion affecting training quality is fascinating and well-supported — that part of the article is genuinely useful regardless of the calorie accounting.
> debunk the popular myth for my friends that exercise burns a lot of calories
Can you expand on that please? Because I can tell you as a matter of fact that when I go for a run for an hour I burn well over 800 calories.
> Can you expand on that please? Because I can tell you as a matter of fact that when I go for a run for an hour I burn well over 800 calories
Sure - how did you arrive at the 800 kcal figure? Most likely a wearable or an app, and those estimates are based on rough linear regressions from weight, age, sex, and heart rate - not actual calorimetry. The error margins on those numbers are significant, but the devices present them with false precision that makes people treat them as ground truth.
Even setting accuracy aside, the framing is the issue. Your basal metabolic rate - just keeping your organs running, blood circulating, cells maintained - accounts for 60-70% of your total daily energy expenditure. Add the thermic effect of food (~10%) and you're at roughly 70-80% of your energy budget spent before you even lace up your shoes [1]. Exercise typically makes up the remaining 20-30%. So that hour of running, while genuinely beneficial for a hundred other reasons, is a relatively small slice of your total daily burn. And not all calories are equal on the intake side either - your body spends 20-30% of the energy in protein just to digest it, compared to 0-5% for fat, so "800 kcal burned = 800 kcal of anything eaten" doesn't hold up.
That's what I mean by "myth" - not that exercise burns zero calories, but that the popular mental model of "I ran for an hour so I earned X calories of food" is built on inaccurate measurements, treats all calories as interchangeable, and overweights exercise relative to what your body spends just existing. Curious though - do you track your intake with the same rigour, and if so, do you find the numbers actually add up in practice?
[1]: https://my.clevelandclinic.org/health/body/basal-metabolic-r...
> That's what I mean by "myth" - not that exercise burns zero calories, but that the popular mental model of "I ran for an hour so I earned X calories of food" is built on inaccurate measurements
Over the last few of decades there's been a lot of lab research calculating the gross efficiency of the human body with different factors (size, sex, fitness etc) and I think these estimates that sports apps give are very close.
If you cycle with with something that can measure power output you can calculate the mechanical work done by the body exactly during that exercise period and convert to energy "burnt" (1 watt/hour = 3.6 kJ = ~0.86 kcal). 220 Watts for an hour (I couldn't do that but a good cyclist can) is about 800 calories.
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I tracked intake, calories burned(from Apple watch with activity tracking turned on for any specific exercise) and weight for 12 weeks as part of 75 hard and found my daily weight decreases were exactly in line with what you'd expect given the estimated deficit 95% of days and 100% at the weekly level.
I don't track consistently anymore only when I'm working towards a goal but when I have more than 2 weeks data these days it seems pretty spot on to the point I can calculate the tracked captors to target to get the desired rate of change in weight pretty consistently.
Thanks for fleshing out your comment. Because initially it did kind of suggest to me you were saying it burns no calories or makes _little_ difference.
I agree with all you posted.
> Curious though - do you track your intake with the same rigour, and if so, do you find the numbers actually add up in practice?
To return the courtesy, for the purposes of discussion I picked a rough estimate and rounded down significantly the actual amount I typically run. More often it's 1.5 hours a run and supposedly >1000 calories given my weight, heart rate, terrain, and speed. I also assumed the calculations are way overestimating my actual calories spent so just went for something somewhat plausible for the sake of a HN comment. As you noted calories aren't accurately reported by devices. I do not pay attention to it in massive detail either. But in practice since I run an average of about 25km a week but can vary from 0 for some weeks to 50 for others and I keep relatively good eye on my diet I notice significant changes in weight over time that tallies with effort. Three months of below that 20ishk a week and I will put on 2-3kg. The next three months I increase to 35ish+ a week and it drops off again. Would I swear to it in a court of law that I'm not miscounting meals? No way. But I feel reasonably comfortable that this is an accurate description.
You are being idiotic. One hour of running is almost half of my minimum energy expenditure. All the other movements in a typical day only account for about half that, unless I make sure to walk a lot more than most people would.
The brain does increase energy expenditure with activity, but as said in the article, it's quite minimal.
I have been tracking caloric input very precisely and energy expenditure with an Apple Watch (one of the most precise trackers) for a while, and I can guarantee you it all adds up.
In fact, once everything is calibrated, I could predict my weight loss/gain with a 5-10% margin of error at worst (mostly due to imprecision in food calorie accounting and inaccurate energy expenditure tracking).
Too many people try to mystify something that is extremely simple. There are some things to care about (like not going too low on the protein), but it really is all about getting the same amount of energy that you are spending, and that's pretty much all there is to it.
I think OP may be referring to the idea that the total number of calories burned in a day doesn't meaningfully change under a workout regime. Working out does burn calories, but after a few session your body starts to compensate by burning less calories in other areas (e.g. immune and reproductive system). The net result is close to zero, except in very demanding workout regimes.
I don't have the background to fully evaluate how true that is. I read "Burn" by Herman Pontzer, which at least makes a very good case for it.
So this is about https://en.wikipedia.org/wiki/Exercise_paradox
I seems like it's only part of the story. If you increase exercise but also increase calorific input to match then you won't lose weight. But, the laws of energy conservation being what they are, I don't think anyone disputes that if you very significantly increase exercise but also maintain calorific input then you will lose weight as the energy must come from somewhere and there are only so many optimisations your body can make. You could of course maintain exercise levels and reduce calorific input for a similar effect, ignoring health benefits of exercise. Take an extreme case, Michael Phelps. He used to eat 12,000 cal a day because of the hours he spent swimming. Certainly not a small guy but pretty lean! So I'm totally prepared to accept there are bounds to all these statements but I still think I couldn't finish an 800 cal sandwich for lunch hehehe.
By the way, I feel the Wikipedia page there uses a lot of words suggesting that the paradox isn't at all fully understood and that there could be compensating mechanisms we aren't aware of. But I'm not in a position to dig deeper.
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Yep, pretty much exactly what I meant.
And also that the calorimetry from wearables is highly flawed and it seems to that we don't have super accurate data and what sort of activities burn the most energy.
I am also a big opponent of folks that start equating the "my wearable shows that i burned 300 kcal with that activity so it zero outs that sweet thing I ate earlier that was also 300 kcal" which is wrong on so many reasons but with a lot of workout apps and devices pushing the (inaccurate) kcal count front and center becomes more and more a of a thing.
I think it sort of depends on how you look at it. If 800 is an hour of running - that's probably "a lot" for quite a few people. But 800 is also just a sandwich. Which isn't all that much.
So if you view this from a time use perspective, just skipping that sandwich is way better than running for an hour. And many people can't spare an hour a day just to make up for a sandwich. Hence - "not a lot" - Its too expensive time-wise for the caloric balance effect it provides. Just skip the sandwich instead.
What kind of sandwiches are you eating? 800 calories is a ridiculously large sandwich.
Even Tesco's bacon & egg triple is only 550 : https://www.tesco.com/groceries/en-GB/products/260422235
I'm struggling to find anything I'd describe as a sandwich come close to 800 calories.
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I agree with the general message, but I'm curious what ingredients go in your 800 calorie sandwich. That's more than a double Big Mac with 4 patties (780 kcal)!
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That's a big sandwich :)
Big Mac = 580 Cal.
I'm going to eat lunch one way or another and for me it's going to be under 800. Skipping meals isn't really a good choice, imo, but ok.
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How can you know this "as a matter of fact"? Because your not-a-healthcare-device sportswatch tells you so?
Not running, but in cycling we have power meters, and some workouts (eg 2 x 20' threshold) will definitely burn in the range of 800 calories in an hour. The energy measured by the power meter for this workout is 800 kJ for me (my threshold being around 260W). Now it turns out the conversion factor from kJ to calories is 1/4, but the body is only 25% efficient when producing calories for cycling, meaning one has to burn 4x the amount measured by the power meter. So that's 800 calories for this kind of workout, for me. I wouldn't be surprised if runners of similar fitness doing similar workouts had the same energy expenditure.
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But you’ve never directly measured calorie expenditure while running, so how can you be certain?
> debunk the popular myth for my friends that exercise burns a lot of calories
Depends on your level of exercise. I often cycle 100km per day and can tell you if I ate only the 2000 kcal I hypothetically need I would go into a strong deficit.
There's been metabolic studies that show that this isn't true. Comparisons of total caloric usage of completely sedentary people and people who have high exercise load are indistinguishable. There is a large difference among individuals, but not correlated to exercise levels. Sedentary people who start training hard will have a spike in caloric usage for a few months, but their body adapts and calorie burn returns to the same level that it was when they were sedentary. This was new research, so there wasn't an explanation for it. The authors hypothesized that it could be that the body reduces caloric spend on other things, like stress responses, when it is adapted to high exercise levels/ They did note that some extremely elite athletes can temporarily increase their caloric burn (think Michael Phelps eating 10k calories per at some points when training for the Olympics) but its not something most people can achieve or sustain.
Absolute nonsense. The claim is that if I produce 2.5watts per kg in body weight for 2 hours, I’m not going to burn any extra calories? So when I “bonk” and exhaust glycogen stores due to underfueling that’s actually not true?
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100km is a lot of exercising...
Try doing 300km in one day, and 100km will seem like cake
> if I ate only the 2000 kcal I hypothetically need I would go into a strong deficit
Right, and that's kind of my point - the "2000 kcal" figure is itself part of the problem. It's a rough global average that doesn't account for your sex, age, weight, body composition, activity level, or even climate. It's a number on a food label, not a physiological reality for any specific person.
And even if you could nail down your actual total daily energy expenditure, calorie counting treats all calories as equal, which they aren't. Your body spends 20-30% of the energy in protein just to digest and metabolize it, compared to 5-10% for carbohydrates and 0-5% for fat. So 100 kcal of chicken breast and 100 kcal of butter are not metabolically equivalent - your body nets significantly less usable energy from the protein. This is the thermic effect of food, and it alone accounts for roughly 10% of your total daily energy expenditure.
Speaking of which - basal metabolic rate (just keeping your organs running, blood circulating, cells maintained) accounts for about 60-70% of total daily energy expenditure. Add the thermic effect of food on top and you're at roughly 70-80% of your energy budget spent before you even stand up from bed [1]. Physical activity - including your 100km rides - typically makes up the remaining 20-30%, though obviously that range is wide and shifts dramatically for endurance athletes.
So yes, of course people who cycle 100km need more fuel. Nobody is disputing that. My point is that most people vastly overestimate how many calories exercise burns relative to what their body spends just existing, and they use kcal as a universal unit of nutritional value when the body's actual energy extraction varies significantly by macronutrient composition. People optimizing purely on calorie numbers are working with a model that's far rougher than they think.
And this whole picture gets worse with wearables pushing calorie counts front and center. You see it all the time - "my wearable shows that i burned 300 kcal with that activity so it zero outs that sweet thing I ate earlier that was also 300 kcal" That's wrong on multiple levels - the device estimate is inaccurate to begin with, the thermic processing of that pastry isn't equivalent to the "300 kcal" on its label, and your body doesn't do neat arithmetic like that anyway. But with every fitness app and smartwatch plastering a big kcal number on your workout summary, it's becoming the default way people think about food and exercise, and it's reinforcing exactly the wrong mental model.
[1]: https://my.clevelandclinic.org/health/body/basal-metabolic-r...
> doesn't account for [...] activity level
That specific aspect might end up irrelevant for dieting, which is exciting since it flies in the face of intuition. It seems that when it comes to long-term modes of existence (as opposed to, say, the one day of the marathon) the "activity level" doesn't really affect how much energy your body uses.
> In this study, we used the doubly-labeled water method to measure total daily energy expenditure (kCal/day) in Hadza hunter-gatherers to test whether foragers expend more energy each day than their Western counterparts. As expected, physical activity level, PAL, was greater among Hadza foragers than among Westerners. Nonetheless, average daily energy expenditure of traditional Hadza foragers was no different than that of Westerners after controlling for body size.
https://journals.plos.org/plosone/article?id=10.1371/journal...
Thank you for your comment. I didn't know about protein and carbs and fat calories not being metabolically equal. I'm hoping that calories counting apps would account that in, but I know that it's probably not the case
Chess lol. Playing a competitive arena FPS a the highest levels will get your brain cooking.
Don't know what's here to 'lol' about chess. Are you implying chess isn't cognition intensive?
I'm suggesting there are other activities I'd expect to cause the brain to burn more calories.
Why would it be more than any other activity that involves making decisions?
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