This is well known in emergency medicine. Not only do kids burn out quick, they also burn out completely because they, unlike adults, don't keep a reserve. This applies to homeostasis, too.
Consequently: young trauma victims that "look OK" need to be very closely attended to, because what you might be seeing is a kid burning the very last of their energy reserves just to maintain homeostasis, and they will NOT degrade gracefully once they're out of energy -- they'll just go right into the deep end of shock. Happy and talking to unconscious in 90 seconds is nothing you want to see.
Not as far into the end as shock but I've learned to watch for the signs that my daughter is tired and crashing. Sometimes it's as small as being a little distant (harder, many possible reasons) to full on tantrum (much easier).
If you've raised a baby, you'll know the concept of "overtired", but it was absolutely baffling to me as a first time parent.
You're tired kid, just go to sleep!! But they won't unless the conditions are right. Miss the window and they'll go into overtired which causes them to scream/tantrum for way longer than anyone wants, again baffling.
yeah, they behave like they're tired, but they have no idea what's going on and they're afraid of the feeling or just don't like how it feels but don't know what to do about it. it's like sleep is independent of their will.
This is very important for any water related activities:
many kids drowned because of this. Jumping, screaming and laughing in the water - the next moment gone. You have to pay attention. I do not mean, being overprotective, just pay really attention to them and you should notice, when they are about to reach their limits.
This made going to the beach pool or local lakes pretty much a full-time lifeguard job for me during the years my kids were young and didn't know how to swim well.
I would let them play, run around, go out in the deep water and even get that terrified "I'm over my head!!" look on their face while they flailed their arms around. It's get to let them stop panicking on their own. They learn their limits and I've only had to actually wade out and rescue them a handful of times.
But I was basically scanning the water and counting my kids (I have five) every minute the whole time they were in the water.
Very good point. My boys are 11 and 9, I can count 3 times I’ve gone in fully clothed with phone/wallet in pocket to pull them out of a pool after getting in trouble. For them, it was panicking when getting in over their head ( heh no pun intended). Panicking in deep water is bad news.
Edit: I distinctly remember one time being at a party surrounded by adults but the only one noticing the emergency. It’s like when a kid gets in trouble with water they become almost invisible… it’s very strange.
"It’s like when a kid gets in trouble with water they become almost invisible… it’s very strange."
Well, it can be hard distingishing kids playing in water loudly and just ordinary play screaming - and kids panicking in water. It looks and sounds the same on first glance in many instances. Or rather not. When they are loud, they still have energy and their head well above the water. (you cannot shout so well, with water in your mouth)
The scary part is, when they reached their limits and do not have the energy to panic anymore and just fade and drown.
If that happens, it is very important to not panic yourself, go in quickly (but not headless) and maybe know some CPR basics if necessary.
There are cases, where the drowned child got rescued, but the paniqued parent drowned dead. Or the other sibling.
(not in pool, but in river/sea type scenarios)
But better avoid that alltogether by paying attention before and choose the site accordingly. I mean I am also very often with my toddler at a river, where he can play at a shallow spot. I know it is dangerous if I stop paying attention to him, because the river has a strong current and rocks in it. And he already knows the dangers, but he overestimates himself quickly. He is the kid. I have the responsibility.
Very true. With two kids in the pool you have to be like one of those auto-tipping novelty birds: you check, you look away at something else, YOU CHECK, you have a splash and a look at the sky, YOU CHECK ...
It's not only about kids. Plenty of people drowning in the same way, without loud cries, just silently. That's just how human brain wired for some reason.
My family recently had norovirus ("winter" vomitting bug), which for healthy adults is pretty much nothing other than being stuck on the toilet for a day (as I was). My 2 yo however was in hospital for nearly a week on an IV because of this.
As soon as my wife realised it wasn't just simple vomitting she called a doctor and they told us to go to hospital, so we were there within 3 hours of the first episode. My wife stayed with them in hospital, but because of corona I wasn't allowed to see them - which wasn't particularly nice for me and I'm sure was very traumatic for our kid.
We have all recovered now, but yes it's somewhat surprising how quickly young kids can go downhill.
A noro or rotavirus ripped through my 2 years olds daycare recently, and in a couple classrooms (including my kid), tons of kids got sick as well as teachers, but did not hear of any hospitalizations.
The first evening was brutal though. 6 hours of drink, vomit, eat, vomit, drink, vomit, etc. My kid easily threw up 20+ times.
If my kids vomit more than once they go on a cycle we've developed over the course of having five young children.
First time, maybe a fluke. Check for other signs of illness, heat sickness, what did they eat recently, fever etc.
Second time they get no food or water for two hours. Then small sips of water/Pedialyte
If they don't vomit after the liquid they can eat a few bites of BRAT (banana rice applesauce or toast) if they do, wait another hour or two and repeat.
If they're still vomitting after 6+ hours, depending on the child's age, we'll call the pediatrician and ask for advice.
If they're still not keeping even liquids down after 8+ hours (again depending on age) we take them to the ER after consulting with the pediatrician again. We've only had to do that once.
If at any time the child shows signs of dehydration we skip to the last step.
Oh man, I always thought my kid had shitty homeostasis but thought it boiled down to just having little mass, I never considered it might be an energy thing!
When I was young I fell unconscious like four of five times and the doctors couldn't find why... If what you say is correct, it could be a possible explanation. Although I was never the very energetic running around kid due to having some complications at birth. I have learned though to notice when I'm about to go unconscious and find a chair or something so that I don't just fall on the ground and hurt myself. I once fell unconscious in a church which was fun because now I can joke that I was touched by the God.
It's quite interesting how much we still don't know, especially about ourselves.
Another thing to keep in mind with infants/very young children is that if they get diarrhea, they can lose 30% of their weight (mostly water) in 2-3 days and die without hospitalization. So that means waiting a reasonable time for improvement at home can actually kill them. (I don't know how that kind of illness affects their future development.)
Same with cats! It's a common reason why many house plants which are toxic to cats are potentially fatal. They die of dehydration, not strictly poisoning.
Personally, I was more surprised by the various groups of people who _don't_ have higher metabolic rates:
> Children’s metabolic rates stay high until age 5, but the rate slowly begins to glide down until it plateaus around age 20. Interestingly, adult rates are stable until age 60, when they begin to decline. After age 90, humans use about 26% less energy daily, Pontzer says.
> The study also found that pregnant women don’t have higher metabolic rates than other adults; their energy use and calorie consumption scales up with body size
> The metabolic rate didn’t zoom up in hungry teenagers either
This seems almost unbelievable to me. Almost everyone I know, with a handful of exceptions I can think of, had a dramatic change in what I can only say was metabolism at 30 declining steeply to 40. I can tell you personally my ability to lose weight when exercising daily has decreased significantly since 30. If it’s not metabolism, then what? Diet and exercise are almost identical.
Without more details if be inclined to blame "almost identical" as the culprit (not an expert):
Making all your meals 5% bigger would cause a weight gain of nearly 10lbs/yr, and the kind of switch in diet that can happen naturally with age (especially including eating out more with friends) can make it hard to spot incremental changes.
Moreover, a lot of exercise doesn't actually do much for weight loss (it's still immensely beneficial for your health; please don't stop). To counteract the aforementioned 10lbs/yr you'd have to walk an extra ~20 minutes per day. It isn't all that much per se, but if your exercise were 20 minutes of something high intensity and an hour of something low intensity every single day (a lot more than most people get) it'd still be a noticeable demand on your time -- enough that I don't think you'd call the extra exercise level "nearly identical."
It's also possible less visible culprits exist if you're used to average weight gains/losses of under a pound per month as a function of your diet/activity. E.g., iirc fidgiting and tapping your feet consumes nearly a pound per month in calories, and that doesn't seem like the kind of thing you'd recognize stopping/starting over a timespan of decades.
> Without more details if be inclined to blame "almost identical" as the culprit (not an expert):
Why? I mean, why do people find the idea of older people needing different diet due to body changes related to age so unbelievable? There are many changes related to age - how quickly injuries heal, how quickly you recover from something physical or tiring, how much or well you sleep. Your heartrate is slowly changing with age too.
Why would it be shocking that these has also impact on how food affects your look?
> To counteract the aforementioned 10lbs/yr you'd have to walk an extra ~20 minutes per day.
That is not how this works tho. The effect of exercise is not just in how many calories you theoretically spent running/walking exactly same distance. Your body adjusts to exercising way more - including on metabolism and body temperature. It has impact on how body works overall including on hunger - depending on exercise it can go both toward eating less or eating more. It has impact on how many muscles you have, how much energy you burn while building those muscles etc.
Experience of "I stopped exercising and keep eating the same, I gained a lot of weight" is not rare.
Because it's much more likely that they're one of the <nearly everyone> who can't estimate calories in/out well than that they're an outlier with a significant metabolic drop in some small number of years, especially given that small misestimations are large enough to yield the observed behavior. Maybe there's something else going on, but "without more details" it wouldn't be the first place I'd look.
> older people needing different diet
Absolutely! I hope nobody took away opposing statements to that from what I said. The double whammy of needing fewer calories and being less equipped to absorb vitamins and whatnot necessitates a significant change in diet with age. I was only commenting on this one person's experience aging just a few years in the middle of their life.
> walking
> That is not how this works tho.
Especially for walking, that's exactly how it works. Walking builds negligible muscle mass, and everything else you've mentioned (aside from perhaps impacts on hunger), adds up to well under a 5% error in calorie estimates -- well under the noise floor from applying a general purpose calorie estimate to any one specific person.
> Experience of "I stopped exercising and keep eating the same, I gained a lot of weight" is not rare.
It's not rare because calories add up immensely quickly. Say that you were burning 200 kcal per day exercising - and that is a low estimate. If you keep eating the same, you end up keeping 6000 kcal per month more - that translates to 1.7 lbs of body weight - per month. So, 20 lbs in the first year!
So the claim is, that simultaneously: 1.) when you stop exercising, it does a lot for weight. 2.) If you start exercising, it does nothing for weight loss.
>1.) when you stop exercising, it does a lot for weight.
Yes, if you also don't downsize your meals at the same time. Which a lot of people don't.
>2.) If you start exercising, it does nothing for weight loss.
Yes, if you increase your food intake because you feel more hungry, which a lot of people do. If you keep eating the same -- then it of course has a noticeable effect.
For exercise to matter in your weight loss, you have to always keep in mind your food intake. It is still very beneficial and should not be ignored!
Sure. I’ve got about 20lbs more muscle than I did at 30. I currently lift 3-4 times a week and run 3.5+ miles 5-6 times a week. At 30 I worked out or ran 3 days a week.
I eat out less now and generally pay attention to what I eat vs just eating whatever is in front of me. Nearly identical meaning proportions are the same but I eat less junk food now.
I was a college athlete, but there’s no way I carried the fitness forward ~6 years without maintaining my college level of workouts.
I realize it’s all anecdotal, but based on my personal experience, the study is really tough to take at face value.
People tend to massively overestimate how much the extra muscle mass matters, and how much they burn during exercise, though, and it takes very little to overcompensate with a little extra food here and there.
I lift too, and for many years I wrote down everything I wrote, and weighed myself every morning. I could tell very precisely how much I burnt, and it tended to shock people on lifting forums who were certain they needed to down lots protein shakes to get enough calories.
At my peak lifting I wasn't huge, but I was around qualification levels for competitive powerlifting for my weight class at the time (I squatted about 200kg, benched 150kg), and exercised 5 days a week.
I burned about 2000kcal/day on average. I tested that many times when bulking or slimming down by seeing how much I needed to increase it or drop it down. And it changed a little as I added muscle, but much less than you might think.
I'd have people arguing with me on fitness forums that there was no way I was burning that little, and that I really needed 3000kcal/day or more, and then complain about why they were adding weight.
People in a more active job would burn more than that, and people with a more active life outside of work and the gym as well, but people are notoriously bad at estimating their activity levels and apply calorie level assumptions that are often many decades out of date and based on far more labour intensive daily lives. Basically the only way you'll know is to track and measure.
I'm curious: how tall are you and/or roughly how much do you weight? Benching 150 kg with 2000 kcal/day absolutely does sound odd compared to recommendations. However, my personal experience also tells me that the regular recommendations might be a bit high.
6'1/185cm. At the time my weight was around 93kg, so 150kg bench was nothing special for my size. When bulking I'd do about 2400kcal. For people pushing towards competitive levels it may well have made sense to go higher to allow exercising accordingly harder, but for me it was just to stay fit so I prioritised staying reasonably lean.
Also worth mentioning that outside of lifting my life absolutely was/is very sedentary, so I did burn less than a lot of people.
EDIT: One thing that will confuse people here is that style of exercise will matter a lot. To reach a 1RM of 150kg on bench meant most of the time I did bench 1-2 times a week for 5 sets of 5 reps of ca 120kg or so. My bench routine took 10-15 minutes. My whole lifting program took about 40m x 3 days/week. I added some cardio to that, but that is not a lot of physical activity. Someone who does bodybuilding on the other hand will typically do a lot more volume.
Yeah whenever I’ve trained for marathons and I’ve not actively worked at keeping myself from eating too much more, I’ve gained weight during the training. Every single time. You do of course burn more calories than you would if you didn’t exercise but most people don’t realize how easily you can eat back those calories and more if you’re not careful.
Exercise isn't always aerobic. Resistance and weight training which causes a muscle buildup can help you lose weight because your Total Daily Energy Expenditure (TDEE) increases while you build more muscle.
Now if you combine aerobic and anaerobic training strategically, while you have your eating habits checked, you can lose that quarantine weight in no time. This is what i am doing now.
While there might be a very small decline in resting metabolism, most of those people are delusional. They overestimate their exercise and underestimate calorie consumption.
I recommend that everyone get an occasional resting metabolic rate test. It's an easy non-invasive test which uses your exhaled gasses to calculate your daily calorie burn. Most people who claim they can't lose weight due to a "slow metabolism" actually have a totally normal metabolism.
I can't say for the cases you named but its easy to overlook small lifestyle changes, like how much someone walked in college vs after. That was one shift for me.
Yes! I went from walking from home down to campus and then all around campus everyday. Plus I didn’t have much money for food. Lots of peanut butter and jelly sandwiches and noodles/pasta. Now, I drive everywhere and sit on my butt in front of a computer most of the day. Plus I can afford much more calorie rich food, and a lot of it. No surprise I’ve put on 40 pounds over the last 20 years since finishing college.
Not sure I noticed anything like this myself. I did see however, around 30, a massive change in work/life balance.
I went from a rather care-free person in my twenties, who took all vacation days he could, worked part-time for stints in junior functions, to becoming a manager and working 55 hour workweeks and less vacation. That tripled my disposable income and reduced my free time by a third.
My caloric intake before this had been somewhat restricted by these two factors: not enough money to have 'eating out multiple meals daily' be an affordable habit. And not limited enough in time to make that habit-of-convenience a necessary one.
Now I can both afford it and time-wise it helps not to have to prepare every single meal anymore. But for my caloric intake this new habit doesn't help.
We're not talking about massive changes here, but even a 5% increased daily intake stacked over the course of years adds up.
Not to mention changes in non-base metabolism caloric expense. Spending so much time on an office chair definitely leaves less time to move the body. Lots has changed about my behaviour. e.g. in my twenties I often spent two nights a month dancing from 1am till 5am, nowadays I'd still go out but it'd be more of a pub-setting, sitting & drinking.
So I do see changes, but I wouldn't necessarily relate them to base metabolism rates. In your case diet and exercise are almost identical but it definitely wasn't for me.
I think I could have this conversation with people of many ages. For me my mid 20's was when I started to notice more weight gain. I've put it down to now working an office job where I am sitting most of the day, as opposed to standing up and walking around in retail. My job is also more stressful which has led me to be less active after work as I just want to "relax" when I get home.
I have no doubt this also means I eat slightly worse food or larger portion sizes. Luckily I've noticed it and started to make lifestyle changes to prevent it further.
I track calories/food quality, weight, plicometry, and exercise (although not all of them all the time). With precise and systematic measuments, I find easily that it's a matter of food quality, quantity, and exercise.
I'm convinced that there are several external factors that make people over 30 gain weight, more than metabolism: work, children, stable relationships and independence.
I also used to think that teenagers are fit without any effort, but if I look at them, this is generally not true. I will start believe people who claim that it's a matter of metabolism when they'll start to track food, weight and plicometry, and will go on a sports (not walking) regime. But not before.
Like most things there's quite a lot of factors to play into this but I would say one of the main factors here is that generally men start reducing natural testosterone production and gradually losing muscle mass sometime after around age 30. Basically, the more muscle mass you have, the more calories you burn to maintain it.
Also to compound this your metabolism tends to adapt to whatever you are doing. Even if you are doing lots of exercise, your body does tends to become more efficient at doing that exercise, using less calories to do the same thing over time. The same is true of running on lower and lower calories, your body adapts to run on less calories so it actually helps to do something of a 'bulking' period every so often to keep your metabolism running at a higher rate and not letting it drop down to 'economy mode'.
If you change nothing from your 20s to 30s, keeping exactly the same calories in your diet and same amount of exercise then you will most likely start to gradually gain a calorie surplus from this loss of muscle and thus start gain some more fat from the excess calories. You'll basically need to reduce calories or increase exercise to compensate.
Also look into what you can do to help maintain/improve your natural testosterone production (better sleep, nutrients like zinc and magnesium etc) as this will help offset it to some degree (poor sleep alone will absolutely destroy your natural testosterone levels). Alternatively you can look into Testosterone replacement therapy, which seems to be quite common these days.
It can't be testosterone alone. I've got the levels of a 25 year old according to my urologist (and yes, he sent me to be checked for anomalies) and I've noticed a significant decline in metabolism after the age of 40, despite exercising and not gaining weight and sleeping more than before. My (unscientific) hypothesis is that it's mostly a mental thing due to work/life being less demanding at this point.
I think being moderately poor really helps with staying thin. A major shift for me going towards my 30s was replacing parties with dinner dates.
Last year during the short lockdown break I went to a birthday party followed by a rave followed by sleeping on a friend's couch followed by a walk of shame home... Like in the good old days. My Garmin said I did 30k steps that night, probably double my previous record. I also couldn't really eat much for two days after that, so there's that too...
I also noticed the same in many people, as well as myself. And I do not think the other commenters are correct in their explanations.
At least in myself, I can clearly see that in my 20s I had a much more sedentary lifestyle, sitting in front of a computer a heck of a lot more, having less social life and eating _much_ worse (processes food, sweets, coke) and still being able to maintain a normal BMI.
If its not metabolism it must be some other mechanisms that allows people to do it, but metabolism seems the simplest one.
I have this 'theory' about 'diet fatigue': the more times you lose weight, the harder it will be the next time. I hadn't associated it with age but with the count of times I (kind of successfully) lost weight through calorie deprivation and sometimes additional physical exercise.
I have this pet theory as well, at least for myself. After being quite sick for 3-4 weeks at 28yo and losing 12-15 lbs, I noticed that since then, my energy levels never returned and my ability to lose weight changed from pretty easy to needing to exercise and diet quite a bit.
What about everyday motions? At 50, I push myself gently up from my chair, while 25 year old coworkers leap up. They walk faster, they simply move with more energy through the day. Such things add up over the course of a day/week/month/year/decade.
They do, and I've lived that. Sincere advice: force yourself to stand up without any assistance from your arms. I had a knee issue for a couple of years, and got into that very habit -- at first out of necessity. Before long it was required. It took about a month (!) to build back up the core strength to stand normally again.
Your core strength will decline quickly, and soon you will have to help yourself up all the time. Don't let the slide happen.
It's a combination of your lifestyle changing and your kidneys beginning to lose function. Your metabolic rate may be the same but your GFR is declining.
Metabolic rates (caloric intake and use) may be the same, but the bodily priorities for where those calories go may differ. That would be my guess anyway.
Disclaiming expertise doesn't have to arise out of fear of lawsuits. It could just be letting people know as a friendly gesture that you're not an expert and that your comment may reflect a layperson's best understanding rather than specialized education in the field.
That’s because nobody knows anything about how our bodies burn energy, just like the article says, and the use of the term metabolism is complete pseudoscience to convey a misunderstood abstract concept.
It does make sense if you think about it in terms of overall calories consumed rather than metabolic rate.
Children are very small and light, so even with a higher metabolic rate they need less calories overall than an adult. However a teenager is usually reaching adult size, but still with the same higher metabolic rate as the child, meaning they will need more calories than a typical adult who is on a lower metabolic rate even at similar size, that is why teenager seem to eat so much.
Pregnant women likewise may not have a higher metabolic rate, but they still need to eat more calories overall then before they were pregnant as they are growing in size and weight. It's not much different to a bodybuilder eating more calories to build then maintain a greater muscle mass.
My 22 month old son wakes up at 5am, and doesn't stop running, climbing, singing and dancing, any possible "activity" you can think of until 7pm when we have to wrangle him for about an hour during "quiet time" until he eventually decides it's time him to sleep. The description "different species" seems apt because I really don't see how it's possible for such a tiny "human" to just have so much energy.
seems invariant across many mammals for toddlers at least: in dogs "the zoomies" for example fits the same description, cats too, unsure what else is comparable
Oh yeah, my two kittens (and any kittens for that matter) were notorious in this matter.
Play like nothing matters for half an hour, run, jump, sprint, crawl, scratch, everything like your life depends on it. And then just fall down on the spot for like an hour or two, followed up by a repeat of the same cycle.
It's cute to watch, but also kind of scary. They just look _empty_ after that intense a playtime.
Are the broad conclusions really that much new information?
Were we really particularly scientifically blind to the basic energy usage as a function of age, or is this a somewhat more precise measure than was available before?
Of course there is a lot of half-accurate folk wisdom about how much you eat when you're growing or old or whatever else, and it's useful to dispel and correct that a bit (but I'm assuming that data already existed)
It would be nice to have the actual advance this study made over previous information be the center of the show instead of an offhand remark which is basically just a joke (both in the title and at the head of the article). It just seems like the important part of the story is absent.
> Scientists know surprisingly little about how much energy we burn throughout our lives. That’s because such data require so-called doubly labeled water studies, an expensive test in which people drink “heavy” water with unusual versions of hydrogen and oxygen that can be chemically traced. Scientists measure the amount of these “isotopes” excreted in urine, blood, or saliva over 24 hours for 1 week or more to calculate how much energy individuals use on average in a day.
I remember an article a while back on HN or Reddit about drinking heavy water. Interesting it’s a way to measure energy consumption.
Seems pretty dumb to talk about them having fast metabolisms and brains all this other forest-for-the-trees. They are going to double their body mass over a year. See how much energy you need if you try that
Might have something to do with the fact that newborns barely move. Lots of kids will get increasingly chunky right up until the moment they start crawling/walking, when they start slimming down. I can’t imagine there’d be increased energy expenditure when you literally can’t roll yourself over, let alone move across a room.
We should also not call someone that wrote a message in a certain way an asshole. You very likely don’t know that person and whether they’re an asshole.
This is why parents are always shouting at their kids to dress warmly, but I remember always being hot in my clothes as a kid and needing to take them off.
In summers I would bathe in cold water until I was blue and then some. My parents said that they used to be worried by it, but they realised I was totally OK. They would keep an eye on me, but if I was out of the bath, pool, or ocean for a couple of minutes I would be right back to warm.
All I remember as a kid is being unusually warm in almost any cold conditions. Even now the cold doesn't bother me much, certainly less than my peers.
I'm sure metabolism isn't everything there, but it probably helps.
> Children’s metabolic rates stay high until age 5, but the rate slowly begins to glide down until it plateaus around age 20
It reminds me of the quote from Rimmer in Red Dwarf - which was also used in a popular student uk song "Surfin’ USM" by the band "Carter USM" - https://youtu.be/_BGlAWeNFOE?t=11
Rimmer/ Red Dwarf: "When you're younger, you can eat what you like, drink what you like, and still climb in to your 26-inch-waist trousers and zip them closed. Then you reach that age- 24, 25- your muscles give up, they wave a little white flag, and without any warning at all, you're suddenly a fat bastard"
This song stuck with me because it happend to me around 22-23, I gained crap loads of weight (around 3 stone/ 42 pounds/ 19kg)
Great quote, but I think the focus of the high metabolism in the research is mainly around the 9-15 months old period and so a sudden and dramatic weight chance in the twenties might be related to some other shift.
This part of the article shows the effect over time, which is much less as time goes on:
"Children’s metabolic rates stay high until age 5, but the rate slowly begins to glide down until it plateaus around age 20. Interestingly, adult rates are stable until age 60, when they begin to decline."
Nothing here that hasn't been a common knowledge in a long time.
As a skipper I have also went through a lot of training for emergencies and children are practically treated as their own category on every step. In particular increased metabolic requirements, decreased ability to survive without oxygen, inability to survive in cold water for any length of time, and so on.
Consequently, when I train my crews before I go for a cruise with them we have separate scenarios for emergencies with kids (assuming there are children on board).
Interesting that there is more variation between people at the same age than there is in the same person across multiple decades. Some of this is certainly genetic.
Stable weight simply means the intake calories are just enough for the spent energy (muscle and brain which still use 20% of energy for adult, for example a chess player can spend up to 6k calories/day when playing)
I wonder how on Earth did they get so much energy. They are active all day all night. I do sometimes wish that I do have that kind of energy after long work hours.
> Infants between the ages of 9 and 15 months expend a stunning 50% more energy in 1 day than adults do, adjusted for body size. These wee dynamos consume and use up energy even faster than pregnant women and teenage boys, most likely to fuel their energetically expensive brains and organs.
> “Little people are not burning energy like small adults,” says Duke University evolutionary biologist Herman Pontzer, who led the new analysis of data from around the world. “They are burning energy superfast … like a different species.”
This is well known in emergency medicine. Not only do kids burn out quick, they also burn out completely because they, unlike adults, don't keep a reserve. This applies to homeostasis, too.
Consequently: young trauma victims that "look OK" need to be very closely attended to, because what you might be seeing is a kid burning the very last of their energy reserves just to maintain homeostasis, and they will NOT degrade gracefully once they're out of energy -- they'll just go right into the deep end of shock. Happy and talking to unconscious in 90 seconds is nothing you want to see.