[MichaelDickens]

In addition to activity levels, you probably just weren't eating that much food. It was similar for me when I was a teenager: some days I would binge on a ton of junk food, but other days I would forget to eat breakfast, and the latter happened often enough that I stayed skinny.

[naijaboiler]

No I legit ate way much much more in my 20s. I'm not misremembering. I ate more

[Loughla]

I had to supplement with calorie shakes for workout guys in my 20's, just to maintain weight. I ate trash, and a shit load of it. And that's not considering the amazing levels of calories I would've consumed from alcohol.

Same activity level now as then. But now if I think too hard about a candy bar I gain weight that never goes away.

[willcipriano]

> Same activity level now as then.

As you go from untrained to trained you burn less calories doing the same activity.

[bennyelv]

It's actually nowhere near as simple as that, and it depends on how you define the "same activity".

Moving your body from one location to another at a particular speed results in a fairly static amount of work done (in the basic physics sense). So if the same you hops on a bicycle and cycles up the same hill in the same conditions with the only difference being that one of you has trained hard for the last 5 years and the other hasn't (but somehow your body mass has stayed the same) then you'll burn exactly the same amount of energy. Untrained you will find it much harder, but the energy burn will be roughly the same.

There are some things that can be different as you go from "untrained" to "trained", for example lighter people burn less energy moving themselves around than heavier people. Trained people tend to do activities harder/faster so the "same activity" could actually be a much harder activity despite it not feeling that way. Although if the activity involves travelling a set distance some of the extra effort involved in doing it faster is offset by the fact that it takes less time, so the difference between the two is not as large as you'd think.

[paulpauper]

same here. the hockey-stick or v-shaped weight rebound if I even deviate a tiny bit. amazing how fast weight comes back on.

[goostavos]

>I'm not misremembering

It's the easiest explanation. As a gym bro that regularly cycles weight, it's is remarkably easy over/under estimate intake just going off recollection. I always think I'm dialed in until I write things down (I'm almost always eating way fewer calories than I think).

[lkbm]

Okay, so just to be clear: the OP is describing a phenomenon that is extremely widely reported, and is doing so in discussion thread about study that also reports finding this phenomenon, and your claim is that the simplest explanation is that OP is misremembering, and the research is just wrong?

Do you have any evidence for this bizarre dismissal?

[scythe]

The study says that TDEE is generally constant from 20 to 60. Multiple studies have shown that on average people do a terrible job of estimating their food intake ([1], [2] for example), especially when they aren't actively monitoring it. Meanwhile the person you're talking about (who isn't properly "OP") is claiming that they ate more in their 20s than they do today without corresponding health effects. This is not consistent with TFA nor with previous research.

1: https://www.nejm.org/doi/full/10.1056/nejm199212313272701

2: https://www.tandfonline.com/doi/abs/10.1080/08870446.2019.16...

[goostavos]

(This thread is now hella old, but only look at comments every once and awhile, thus the late reply).

I'll just say the same thing I always say in these kinds of "who are you to deny science!?" replies. For everyone championing how hard, complex, and subtle weight loss is, there's a "dumb" gym bro just weighing him self every day and dialing back calories until the scale starts going in the right direction. It works every single time. 100% of the time.

[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.

[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.)

[ashconnor]

I was rake thin until I started lifting weights with a buddy of mine at university. However it wasn't until I started GOMAD that I noticed any muscle and weight gain.

Before that I was eating crap. Lots of things that I that were high in calories but not enough of them throughout the day to exceed my metabolism or get close to the amount of protein I needed.

I think if you could go back in time and count the calories you probably were eating as much as you think.

[eastbound]

Maybe lifting weights => Body actually uses and stores all food => Fat at 40?

Whereas a thin man who doesn’t do sports never gets really fat?

[tuatoru]

N=1, but visceral fat starts building up sometime after age 40 anyway. About 52, in my case.

[carstenhag]

Yeah, but likely you walked more. Cycled more. Ran more. Stuff like that.