Muscle burns more energy than fat. As people age, their muscle mass declines without sufficient exercise, so we'd naturally expect the average person's metabolism to decline via this even if "metabolism per kg muscle" didn't change.
In the paper they say that the daily energy expenditure matches well a function of the fat-free mass (a power-law function, at high masses the energy per mass ratio is lower than at low masses).
Therefore all their data is based only on fat-free mass, i.e. total body mass minus fat mass.
So all their conclusions are not influenced by the amount of fat vs. muscle.
But on the other hand, adding either muscle or fat burns more energy period, and we watch the average person's weight gain somewhere between 10 and 20 pounds over the first half of adulthood.
So we could easily expect the average person's metabolism to increase as well, simply to support the extra body mass regardless of composition.
Balancing out the two effects can only really be determined through careful statistics, and is going to be extremely variable per-person.
The article states the difference is small, but also notes “ The majority of the population exists in a range of 200-300kcal from each other”.
All things being even 200kcal difference per day is about 20lbs per year attributed purely to metabolic difference. Now you can say to just eat 200kcal less per day, but those little differences on a daily basis add up.
> All things being even 200kcal difference per day is about 20lbs per year attributed purely to metabolic difference.
As you gain weight, you burn more energy, even just being idle, so 200kcal doesn't means 20lbs per year (obviously so, as otherwise you'd gain 600lbs in 30 years).
An extra 200kcals per day implies gaining extra weight until the extra energy you burn cancels it out, and then stabilizing there. IIRC the rule of thumb is ~25kcal/day/kg so you'd just naturally balance out to being 8kg heavier than the baseline.
200-300kcal seems like an awful lot. Would the higher end of that scale, 300, apply primarily to larger men who burn alot more calories?
In the case of two small women who burnt <=2100 a day, a 300kcal difference would be the difference between one of them fasting for an entire day every single week and the other not.
Metabolic differences are why for a person of my height a weight of 68kg is normal but a weight of 86kg is also normal. Metabolic differences alone don't explain why many people of my height weigh 100kg and more.
totally valid point. I would expect most people to be surprised that the variance is typically smaller than a spoonful of peanut butter, but the nature of gaining or losing weight is such that even a spoonful of peanut butter over years could be the difference between many pounds of body mass.
It def. adds up. To get an idea, consider cancer cachexia , which is involuntary weight loss due to cancer. Weight loss in the setting of cancer is not just due to appetite loss from side effects of treatment and sickness, but also from metabolic changes. It's such weight loss that brings the cancer to the attention of the doctor, and can be quite dramatic despite the patient not changing his or her appetite or other routine or feeling sick at all. How much of an energy deficit is this? it's believed that cachexia only causes a deficit of only 200 calories/day, but this enough to produce dramatic weight loss.
muscle burns very little calories, and even pro bodybuilders who have lots of muscle quickly put on fat off-season when not dieting. I don't think this explains it.
Muscle tissue burns 7-10 calories per pound per day. This means someone who gains 100 pounds of muscle (e.g. from 150 lbs untrained to a 250 lbs bodybuilder) would increase their metabolism by 700-1000 calories, almost a 50% increase in the average daily male calorie requirements of around 2000 calories.
It is essentially impossible to put on muscle at their size without also gaining fat, because they need to be in a large caloric surplus. During the off-season, pro bodybuilders are still training, they just increase their calorie intake significantly. Muscle does burn quite a few calories passively, it's just not nearly enough on a 260lb man to cover 6k-10k calorie intake.
There are multiple factors in maintaining bodyweight: diet, activity level, muscle mass, metabolism, etc. We shouldn't expect a single factor to explain everything, but holding eveything else constant, more muscle and the physical activity necessary to maintain it will burn more calories. It's an important part of maintaining health as we age.
they put on fat because the body fat level they compete at is unsustainable for long periods of time. additionally gaining fat is unavoidable when trying to gain muscle past a certain point.
I would argue they are not "gaining" fat, rather they are "balancing" the amount of fat the body considers normative. Of course you can easily acquire more fat with an inappropriate diet consisting of too much sugar, but a healthy diet will see your body maintain the ratios that are optimal for your current requirements.
It never ceases to amaze me that we think that we know better, and yet the human body, as with other animals etc, have been around for quite some time now. Even if we had all the data from the past that we think is important now, we still wouldn't know better.
There was a post the other day regarding "The prosecutors fallacy" that might fit well with this sort of subject matter.
Over my life I’ve been close to a small handful of perpetually skinny people who thought they had high metabolisms. In every case, when I watched them closely, I realized they barely ate anything.
My ex-gf was one of these people and would routinely tell people about how she could eat anything and not gain weight. But when I would go on a severely calorie-restricted diet I was still eating more than she did on a normal day. I don’t think she was lying about being able to eat anything, I think she just didn’t realize how little she actually ate.
> In every case, when I watched them closely, I realized they barely ate anything
I know people (mainly Asian guys that are trying to build muscle) that seriously struggle to eat at a calorie surplus. So maybe it's not "metabolism" (which there are significant differences between humans) but also differing levels of hunger.
There is a biological feedback loop that dictates how hungry you are via hormones such as ghrelin and leptin.
My little brother is about 50lbs lighter than me at the same height and we have very different builds and all his attempts to bulk fail for the same reason: no appetite. Meanwhile I’m overshooting my bulks and have to cut harder because I love eating too much.
One individual, Michael Rea, weighed (at the time of publication) 115 lbs at 6-feet and subsisted on a diet of 1900 calories a day [0], which he tracked meticulously. It's hard to convey with words how incredible this is. To put this in perspective, Ansel Key's subjects had to diet down to 1,500/day to get almost as thin. Super-fast metabolisms that cannot be explained by undereating or pathology do exist.
Michael’s regimen of 1,913 calories a day is exactly that: 1,913 calories every single day, 30 percent of them derived from fat, 30 percent from protein, and 40 percent from carbohydrates. Cooking for him is the same elaborate exercise in dietary Sudoku it is for all CR die-hards, only more so.
This is more impressive than even Terrance Tao in terms of outliers...nuts. Unless you tried to lose weight of study this stuff, this is no small feat. Pro bodybuilders have to eat less than 1200/day to get super-lean and this is with tons of muscle helping. This guy does it at 1900. If there were a Tiger Woods of metabolism, this guy would be it if Tiger Woods could play better golf.
In my early to mid 20s. I had to go on intentional ingest nearly 5k a day just to gain 10 lbs. As soon I returned to my regular diet, I lost it all. In my early 40s, I dare not even eat half ass much as I did say 25, I will blow up like a balloon. My own lived experience makes me doubt the universality of that "metabolism doesn't change with age".
Maybe metabolism doesn't change, but my ability to convert what I put into my mouth into weight gain has definitely changed for me. As a young man, I used to eat way much more and poop way much more. It was like the food was just passing through, without really getting in my body. No matter how much i ate
Just came right out
Why is Michael Rea considered exceptional here? For that height and weight, that's pretty much bang on what you'd expect as a maintenance level of calories assuming he does any physical activity at all.
trying to get that low of a weight would entail significant metabolic adaptation, which calculators do not account for. Take a 180lb 6-foot male and try to get him to 115 and you can be sure it will take way fewer than 1900.
Was he sedentary, or did he run 10 miles a day? I see no reason to believe his metabolism was unusual without more information about his physical activities.
Michael can stand up in the morning, let alone jog twenty miles a week. But jog he does, and if the results of both his latest physical and the latest CR research are anything to go by
This is 3 miles/day. not that much. Minnesota starvation experiment subjects had to walk 22 miles/week.
I just spent the last six months dieting down to 6% bodyfat and I haven't once gone under 2000 calories. Other than women, I know zero bodybuilders who can sustain anywhere near 1200 a day. Hell, Neggy Shelton's death was just exposed in the Washington Post from extreme dieting and she was doing about 900 calories a day, plus 2.5 hours of steady state cardio, and she was a 124 lb woman.
Those Minnesota starvation study guys you're referencing had to use an extreme deficit to get down to concentration camp weights like that over the course of a year. It doesn't say in there, but that article with Michael Rea was written in 2006, and finding other stuff on him, he seemed to have been doing calorie restriction since at least 1999. A small calorie deficit can add up when you keep at it for a very long time. Even if his TDEE was 2200 or so, that would drop 30 pounds or so in a year eating 1900.
For whatever it's worth, I've been that size, and it was not on purpose. I grew very quickly in middle school and was extremely active. By 8th grade, I was 6'2" 120 lbs and it took many years before I got much bigger than that, and I used to buy entire boxes of donuts, Little Debbie snacks, and family-size bags of potato chips on the way home from school and eat them in addition to the pizza and cheeseburgers they served at the school. And when I got a car and started driving all my friends home, we'd usually go by McDonald's every day, and in addition to just the actual food, I'd get a McFlurry, pretty much every single day.
But unlike everyone else who seems to be wondering how that was possible and what happened when they were skinny in youth, it's not a mystery to me at all. I sometimes played basketball for 18 hours in a day. When I was driving my friends home, that was usually after cross-country practice, running for up to three hours after school. I walked or rode my bike everywhere. I almost never sat down. I rarely even slept. I could eat basically anything because it may as well have been the Michael Phelps Olympics diet. I was insanely active and using a ton of energy every day.
And yeah, when life normalized in my mid-20s, I too gained a bit for a short while, then I adjusted and ate less, and now I'm very lean again, but also bigger because I started lifting and learned to eat on purpose, in an intentional, measured way calibrated to actually meet my energy needs, not just ad hoc having whatever I crave at any given minute and not thinking about it. I understand why people don't want to do this. Even though I'm not restricting like him, at least not permanently, my diet habits are basically like Michael Rea's. I weigh everything, prepare all my own food, and eat pretty much exactly the same thing every day. It probably sounds like a slog and people want to just free graze and wonder why we can't live like humans must have lived for most of the past 300,000 years, when diets and hunger levels seemed to calibrate to energy needs automatically, nobody thought about it, yet almost nobody was fat except a tiny number of super rich idle nobility. But that isn't the environment we live in any more. People are extremely sedentary and randomly selected food from anywhere is utter trash loaded with extra calories in every possible form for no good reason. Unless you have the activity level of a middle schooler from the 90s or an Olympian, you need to actually try.
Show me their Cronometer.com food/calorie diary and we'll see if the proposition even holds. Until then I'm not even willing to grant it's a thing.
In every case I guarantee they eat a normal amount of calories but feel like they eat a lot because they eat slightly more calories than normal in a single meal.
Like me eating two entrees at dinner at 16 and wowing everyone even though I skipped breakfast before school to play Runescape and had a tiny school lunch.
One time I tried to gain weight just to check if I was able to, as I have been unable to gain any significant weight in a variety of situation (sport, not sport; young, not that young, better/worse diet). I ate a calorie surplus diet (I don't remember the exact numbers, it was a few years ago), which meant eating more than usual but not too much either. This was measuring calories, weighting everything, all the drill; meanwhile I wasn't doing exercise other than walking/biking to places. Again, I don't recall the numbers but I gained maybe 10% of what I was supposed to gain. I've also seen how eating the exact same as other people (sometimes more) results in the other person gaining weight and me losing it, despite the differences in exercise being fairly irrelevant.
I'm not saying metabolism doesn't vary among individuals, I'm saying for a given individual, their overall metabolism could decrease as they age due to having less muscle mass even if their rate per kg muscle didn't change.
What you say is true, but the main point of the paper is that they have measured a decrease of the metabolism after around 62 years even after correcting for the body composition, so the less muscle mass explains only a part of the decrease of the metabolism for older people.
The rest is likely to be due to slower rates of protein synthesis for the renewal of various body parts.
Then why can't someone just make an exercise program that replicates this fidgeting. How is fidgeting more potent than 10,000+ steps/day , which a lot of people do but still stay fat.
Fidgeting can make a big difference, at least it’s appeared that way in a couple sources I’ve seen referenced here in the past - failing to have those handy I found this:
https://pubmed.ncbi.nlm.nih.gov/15681386/
No idea how accurate it is, but an extra 350 calories burned is a pretty big improvement over _not_ having those burned.
I doubt fidgeting alone is sufficient to keep most people skinny. There’s a lot that impacts our weight. But if somebody’s automatically burning calories because they have a hard time stopping fidgeting, that might ease the load a bit so they could eat a bit more or walk a little less than would be the case without it.
EDIT: it feels worth mentioning that fidgeting can be an all day activity for some people, 8+ hours. Walking 10k steps takes maybe 1.5 hours, more or less depending on the persons speed. It wouldn’t be as much of a workout replacement as a whole lifestyle change.
You may as well ask if John Carmack is so productive because he's really motivated, why can't someone "just" make a productivity program that replicates this motivation, and then we can all be that productive. How is 'motivation' more potent than 8hrs/day which a lot of people do and still aren't as productive.
What makes you say fidgeting is /a/ movement? Fidgeting is likely a combination of many positive and negative things; I can imagine: more anxious people are subconsciously wanting an escape from a situation and fidgeting more, more energised and impatient people are itching to hurry things up, more musically or rhythmically interested people are grooving with internal beats and earworms, uncomfortable people are pushed to move by their chair/clothes/posture/tools, it could be a form of stimming behaviour such as enjoying the feeling of the movement of clothes against skin or the finger movements taking some concentration and helping focus.
And on the negative side, non-fidgety people might be more depressed or anxious mentally, more physically drained or fatigued or lethargic physically, may have had upbringings where movement drew negative attention from adults telling them to sit still, may have social upbringings where fidgeting was seen as 'acting out', may have been part a band or group where being still was trained into them, may find their own movements distracting or annoying...
The problem is fidgetting seems to be a feedback mechanism.
Often those who fidget a lot will fidget less on days where they have used significant energy intentionally. Or will fidget less if they are restricting calories.
It would be hard to purposefully fidget a significant amount, but I suppose it could be trained with the right monitoring and stimulus. It would probably be better to train some other behavior though.
The question is about base metabolic rate, not energy expenditure from exercise.
Fidgeting is a non conscious act performed throughout the day, it is not exercise. Exercise can actually reduce fidgeting and this shows up in athletes lower BMR that needs to be taken into account for meal programmes.
It is easy to eat more calories than are used in taking 10.000 steps.
This is exactly the kind of clear headed reasoning from prior knowledge I love coming to Hacker News to see. You're right. Thank you for the extra bit of gym motivation.
Therefore all their data is based only on fat-free mass, i.e. total body mass minus fat mass.
So all their conclusions are not influenced by the amount of fat vs. muscle.