Comment by logicchains
1 year ago
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.
There's good evidence that metabolic rate does vary, but not significantly.
https://examine.com/articles/does-metabolism-vary-between-tw...
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.
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"Even when you’re sleeping at night, the brain consumes roughly as much energy as it does during the day."
https://www.brainfacts.org/brain-anatomy-and-function/anatom...
Does this change over time also?
I wouldn’t trust a site called BrainFacts to be unbiased given the source.
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.
Putting on 100 lbs of muscle is impossible without steroids for 99% of people even with 10-15 years of constant training.
Estimates vary but 50 lbs of lean muscle mass is generally considered the natural maximum for men.
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Someone in their first year of consistent serious training can realistically put on 15 pounds of muscle. The year after that it drops to 5 pounds.
That is an insane amount of training - big lifestyle changes!
I increased my calorific needs by 1000 a day by doing a 10K run (1hr) before breakfast.
Still a 160lb weakling :)
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Do you have a source? I would expect the first pounds of muscle to affect metabolism more than the 100th pound, but that's my immediate intuituion.
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.
A lot of skinny people have high metabolism, how do you explain that?
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.
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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.
[0] https://nymag.com/news/features/23169/
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.
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Skinny people almost always eat less even though they tell you otherwise. In closely observing most, they eat less
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.
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Those skinny people most likely have a very inefficient metabolism or at the very least a very adaptable one.
Their mitochondria use UCP1 [1][2] to generate more heat when producing ATP, thus wasting energy that would otherwise be converted to fat.
[1] https://en.m.wikipedia.org/wiki/Uncoupling_protein
[2] https://en.m.wikipedia.org/wiki/Thermogenin
so built-in DNP
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.
Yeah I agree muscle is a big factor, given you use it too
Casual factor. Higher base metabolic rate means less energy available to build body mass.
Fidgeting.
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.
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Well, now I have an excuse for when people asks me to stand still. "Sorry, I cannot, I'm burning calories".
How do you know those skinny people actually have high metabolism? Have they quantified it with a resting metabolic rate test?
I have two friends like that, both were diagnosed with thyroid issues
So to answer you question, hormones
Likely genetic, such as beta adrenergic receptors.
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.