is fast metabolism really a myth?

[rumiakthar]

I realize a lot of people who claim they have a fast metabolism are really just not eating enough but is there really no such thing as a fast metabolism? I feel like some of us get away with eating more while not getting noticibly fat.

 

[esperanza20]

@rumiakthar Your basal/resting metabolic rates will vary with your age and body composition, are generally higher for males than females, and vary between individuals even if those factors are all the same.

meta-analysis

 

[kvolm]

@rumiakthar You have to understand the difference between BMR and TDEE.

BMR (basal metabolic rate) is the amount of calories your body would require to function if you were in a coma. The variability of BMR between people varies somewhat, but not much.

TDEE (total daily energy expenditure) is the total number of calories you burn in a day both at rest and through activity. This can vary WILDLY between people for a huge variety of reasons. Usually when people refer to a “fast” or “slow” metabolism, they’re actually talking about TDEE.

 

[rumiakthar]

@kvolm do we really need to know our tdee if we know how many calories we need in all?

 

[kvolm]

@rumiakthar Do you mean BMR? If so, no, it’s not important. TDEE is the one that matters.

 

[rumiakthar]

@kvolm yea but it says online you have to use or bmr to calculate tdee so wouldn't you need to know both?

 

[kvolm]

@rumiakthar No you don’t. Go on a TDEE calculator website and type in the stats it asks for (usually height, weight, age, and activity level). That will give you a ballpark estimate of TDEE.

Based on that number, adjust your calories according to your goals. Weight yourself regularly in the morning before eating and track the weekly average of that number. If it isn’t moving in the direction you want at the rate you want, adjust calories accordingly.

 

[rumiakthar]

@kvolm not sure why my trainer is telling me I don't need to worry about my tdee but I may stop paying for sessions

 

[davebhere]

@rumiakthar Because there is a prevailing narrative even among a lot of fitness professionals that "(kilo)calories don't matter" as if the laws of thermodynamics don't exist

Yes it's vastly more complicated than that and there are huge social, behavioural and endocrinological variances between people and there are so many different feedback loops and ways to fail that 90+% of people don't long term succeed...

But 4,184 joules is 4,184 joules, and no amount of activists saying "some people still get fat eating less than their TDEE" makes it true.

If you eat less calories than you burn, long term, you lose weight. If this is not true, then entropy is not true.

 

[rumiakthar]

@kvolm nvm I think I read it wrong

 

[thunderchildau]

@kvolm do you know if theres a way i can find out my BMR?

 

[kvolm]

@thunderchildau There isn’t a practical way to directly measure it but you can calculate it with an online calculator. This isn’t particularly useful because it doesn’t actually matter. Only TDEE matters.

 

[veroch]

@rumiakthar

I feel like some of us get away with eating more while not getting noticibly fat.

I think everyone overestimates and underestimates how many calories they're actually consuming. I was once severely underweight due to an illness and had to count my daily intake so I could steadily increase it. It was really eye opening. I thought I was eating a lot but in reality my average daily calorie intake was relatively low.

 

[kayardee]

@veroch Ahh you must be better now then.
I think its great to be the ideal weight for your height.

 

[n1k0l4t35l4]

@veroch So many skinny people try to say they just have a fast metabolism, meanwhile they're never finishing a meal lol. I don't think they realize how much some people eat. It's just like how fat people say they don't even eat that much.

 

[anon103]

@rumiakthar Your metabolism is just an umbrella term for all the chemical reactions going on in your body at any one time (not only the ones involved in burning calories!) It's not really accurate to call it "fast" or "slow", so the term "fast metabolism" isn't scientific.

That said: yes, people burn very different numbers of calories. The bigger you are and the more active you are, the more you'll burn, in general. But even if you have two people the same size and the same activity level, one might burn 2500 and one might burn 3000 because people are different! Your calorie burn also changes over time and with different circumstances.

So these things can be true at the same time:

• Some people have an easier time than others staying skinny.
• Everyone has a calorie intake level that will result in gaining weight. That number will be very high for some people and very low for others.

Here's a deeper dive on that question: https://macrofactorapp.com/metabolism/

 

[rumiakthar]

@anon103 I used to think that people who have an easier time staying skinny have a fast metabolism and those who can fat much easier have a low metabolism.

 

[londonmum]

@rumiakthar Quite the opposite! The bigger you are the more calories you need to maintain weight and vice versa.

 

[mommajulesberry]

@londonmum that being said

if the small person with a higher BMR bulked, their maintenance calories would all else being equal be even higher.

if the fat guy with a lower BMR cut, their maintenance calories would all else equal be even lower unless they built a bunch of muscle or became a lot more active because they felt better/made conscious lifestyle changes.

 

[stchristopher]

@rumiakthar Basically, yes. When most people claim someone has a “high metabolism” they are really referring to their overall energy expenditure (TDEE). What “fast metabolism” scientifically refers to is the BMR (basal metabolic rate) which is how much energy your body expends completely at rest, like in a coma. I’ve made several observations on comments about people who seem to be able to eat as much as they want without getting fat:

• their TDEE may be higher because they exercise frequently. This is the most obvious one.
• their TDEE may be higher because they are more active in daily activities. I believe this is most responsible for the “fast metabolism” belief. Some people expend a lot of energy just doing… seemingly nothing. They move a lot. People with anxiety who fidget constantly, keeping their heart rate elevated a lot. People who pace while they talk on the phone. People forget things and walk back and forth constantly because they forget where they left things. These things add up and it accounts for more energy expenditure than you might think.
• their BMR may be higher than average for their weight/height. This has been shown to vary from person to person but not much, maybe +/- 100-300 calories which isn’t even half of a Big Mac.

People with “fast metabolisms” may have a combination of all three. Also, we usually don’t spend every waking minute with these supposed fast metabolism folks. Some people eat one enormous meal and that’s it. They might eat a lot when they see you and eat little to nothing the rest of the day. Eating habits vary a lot and you don’t know how much someone’s eating unless you count their calories for a week.