Comment by jahnu
6 months ago
> 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.
To the degree the body diverts any housekeeping or thermogenic calories to exercise calories, which from basic biological adaptivity and thermogenic control must be true at some level, that math will be misleading.
Not that doing x work doesn’t burn y energy, but that +x work in exercise does not burn +y energy at the end of the day.
Exercise is an alternate heat source, approximately 1-to-1 with thermogenic heat (albeit, not distributed as evenly). So much so that our body has to switch to cooling strategies.
And the body can respond to exercise expenditures by reducing other expenditures and using calories more parsimoniously in other dimensions.
It is interesting that during periods in which I have a habit of daily low intensity exercise, I feel like I have more energy than periods I don’t do any exercise, even if my calorie intake is the same.
Another noticeable effect is any allergies from local plant life I get clear up quickly during and after exercise. My immune system runs a tighter, less reactive ship.
Those baseline calories are not just often underestimated in a static sense, but are also dynamically adaptable.
One reason may be is that we evolved to burn far more overt calories through a day than our extra-exercise day burns. Our body has mechanisms for storing surpluses but almost certainly raises baseline use as well. Which is easily diverted back to exercise.
On the other hand, beyond any net expenditure from regular lifting weights (as work), to the degree greater muscle mass is achieved and maintained, weight lifting directly raises the body’s baseline expenditures.
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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.
> I don't think anyone disputes that if you very significantly increase exercise but also maintain calorific input then you will lose weight
This is exactly what is disputed by the link you posted. They measured directly the energy expenditure (the number of calories burned by respiration) in a high-activity hunter-gatherer tribe, and in relatively low-activity industrialized societies, and found they were almost the same. So the number of calories the people consumed was not measured or relevant (and must also have been roughly the same if neither group was actively gaining weight).
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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.
Footlong Spicy Italian at Subway ($10 sandwich) is 1320 cals.
EDIT: the trend holds pretty well at the footlong size (which is a big sandwich). 18/26 sandwiches they offer are >1000 calories.
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Fair enough, but so is 800cal/h exercise. And I'd rather overestimate the intake.
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)!
Maybe the Elvis sandwich
https://en.wikipedia.org/wiki/Peanut_butter,_banana_and_baco...
Lots of mayo.. and butter. It's more like a butterich, realistically. ;)
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.
You need to eat roughly somewhere between 1300 and 2000 Cal every day to maintain your weight even if you are doing to exercise at all.
If you want to lose weight, it's far easier to remove 800 Cal from your diet, at least time wise, then it is to exercise 800 Cal's worth every day.
Either way, if you're losing weight at any appreciable rate, you will feel hungry (at least if it's not chemically induced in some way, such as chemo or GLP-1 inhibitors or similar). That's just something you have to get used to if you want to lose weight.
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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.
I'm not arguing that your body burns that much energy, that follows from the first law of thermodynamics.
But whether that means that your body will have a calorie deficit of that same amount, that is much harder to prove.
But you’ve never directly measured calorie expenditure while running, so how can you be certain?