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0 pointssdfhbdf1mo ago0 comments

> 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...

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helsinkiandrew1mo ago

> 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.

Nevermark1mo ago

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.

BobaFloutist1mo ago

>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.

In the same vein as much of the rest of what you're saying, the other thing that I feel like people always neglect with their "Calories in/calories out" and "Bodies can't violate thermodynamics" is that the human body can adjust how efficiently it processes food, colloquially known as a "slow" or "fast" metabolism.

While it's true that the human body has no answer to a true calorie deficit (except the incredibly powerful and effective one of tweaking satiety and hunger signals), as long as you're eating more calories than you're strictly burning, your body can simply take longer or less time to digest the food you put into it and extract more or less energy from what you're eating, which can make an enormous difference without you changing your intake at all. Which means that people can absolutely eat identically, have identical appetite levels, and have extremely different body types.

If you're exercising more, sure, your body will make you more hungry, but it will also work harder to squeeze every possible calorie out of what you're already eating. If you cut down on what you eat, your body will work even harder at it, to the point that you could literally eat less, work out more, feel hungry and tired all the time, while getting fatter, because your body is worried that you're in a famine and in a physically stressful environment and is desperately trying to signal to you to conserve as much energy as possible, eat as much as possible when you find food, and at the same time trying its best to make the most of the food you give it.

And at the same time, someone else's body might simply not do that. It's crazy!

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sanswork1mo ago

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.

jahnu1mo ago

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.

seec1mo ago

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.

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