[Jenda_]

I don't understand where does the excess basal energy expenditure go. Do persons like the OP when <25 y.o. produce significantly more heat (e.g. wearing only t-shirt and shorts even in winter, and "dying" in the summer)? Does the skinnier body mean way bigger heat losses, even when compared to bigger surface area after getting fat (i.e., way higher surface temperature)? (presumably yes, but to this extent?) The article states that the basal expenditure increases with "fat free mass", so someone fat but muscular will have this "overheating" problem even stronger?

[naijaboiler]

one possible explanation for me, calories ingested != caloric intake. I ate more, pooped more. So even if my body's metabolic efficiency didn't change, perhaps my ability to extract calories from what i ate changed.

Sitting down and eating 6 plates of pasta at Fazolis all-you-can-eat for $4 (or $6) + 12 breadsticks every wednesday evening, is not something you can misremember. i was a broke student, and it was most economic meal i used to have. Working at mcdonalds and eating double quarter pounder meal + extra quarter pounder + shake is not something i can misremember. clearing a tub (not a pint) of ice-cream at a sitting is not something i can misremember. setting timer to dliberately eat 6 times a day all summer in order to forcefully gain wait, is not something i misremember. emptying an entire box of cereal in a sitting is not something i misremember. Eating 25 big wings to the bone at a sitting is not something i misremember. And i was all of 130lbs max. It really is insulting to suggest that the likely explanation is that I am misremembering.

In my 40s now, eating a lot is day like today when all I ate was jamaican takeout that i ate most of it. and that's on the high end of what i usually eat. i strictly drink water and black coffee, nothing else. my entire 20s was pop and juice. thats easily another 400 calories daily. I am 150lbs now.

[layla5alive]

I believe you, naijaboiler.

Posts like Jenda's are depressingly unimaginative.

I wish HNers, and people in general, would learn some biology, and use some critical thinking to imagine that when something doesn't fit their very basic mental model, that's probably because there's exponentially more to know/learn(!). Maybe then they would stop thoughtlessly regurgitating such basic misconceptions.

Biology has so much complexity, but so many people want to insist calories in MUST balance calories out, without any exceptions. As if humans are just burning our foods at 100% efficiency in a bomb calorimiter. Biology isn't this boring.

Forgetting digestion and a host of other variably efficient processes, Mitochondria produce ATP from various possible substrates. These substrates are not equally efficient at producing ATP. So just here, in the simplest form, you have a mechanism by which input energy can be wasted or conserved.

Separately, when demand for ATP has suddenly ceased, Mitochondria can change modes to deterministically waste huge amounts of energy to avoid over-producing ROS. So even in the same cell, even provided the same substrates, efficiently can be dialed up and down rapidly.

And we haven't dug deeply into anything. There are so incredibly many processes with highly variable efficiency.

There's much more that we have yet to learn than that we know. Don't underestimate the complexity of biology.

[Jenda_]

> Posts like Jenda's are depressingly unimaginative. I wish HNers, and people in general, would learn some biology, and use some critical thinking to imagine that when something doesn't fit their very basic mental model, that's probably because there's exponentially more to know/learn(!).

That's why I was not disputing the premise (like previous commenters did), but asking for possible explanations!

[layla5alive]

I apologize, you're right - you were sincerely questioning "where does the energy go?" - which is laudible. I mistakenly read your post as insincere and lumped you in with the others who were being dismissive. I should have directed my criticism at grandparent posters.

There's definitely a heat-loss phenomenon - look for skinny kids in shorts in 40 degree weather - but it's also the case that a variable amount of input calories can be discarded without full digestion by the body - energy not even extracted for use. The religiously calories in : calories out folks assume a linear digestion efficiency relationship between total calories consumed and that this holds unifomally across the population. Given the complexity of biology, they should be unsurprised that there will be myriad outliers

[naijaboiler]

this. Yes the physics of weight is ridiculously straight forward. Its first law of thermo (calories in = calories out). The biology is incredibly complex and that's before we get to the pyschological, to the point of making CICO too overly simplistic to describe actual practical reality. The body is not some perfect energy converting mechanical machine.

People also forget "metabolism doesn't change with age" narrative is a based on a paper that used population-wide statistical model. That approach measures "average treatment effect" and is directionally useful in general but incredibly unhelpful in addressing individual differences and nuances. Something is true on average does not mean it is true "for every" or even "for any"

[lkbm]

Skinnier would mean more surface area to volume, but less surface area total.

If we're just looking at energy in and energy out, it could partly be less thorough digestion. I wonder if there are poop studies that find more leftover fat or carbs in faeces of children.

[layla5alive]

Yes - for example: overconsume fat to an extreme degree and watch the color of your stool turn towards white/clay, and watch it start to float, among other notable changes (size, shape, consistency, odor, etc.)