Someone with a fast metabolism or fast BMR burns a lot of calories even while at rest. If you have a slow metabolism or slow BMR, your body needs fewer calories to keep it going.

A fast metabolism does not necessarily lead to thinness. In fact, studies show that people with overweight/obesity often have fast metabolisms. Their bodies need more energy to keep basic body functions going.

It would be also good to add that thyroid disorders may lead to weight gain by means of metabolism change according to this source as well—it’s not just a matter of appetite.

Like 99.9999% of health, nuance is important and blanket statements like “fast metabolism has been disproven” are just… unhelpful.

[–] JeffreyOrange 7 points 4 months ago (3 children)

https://pubmed.ncbi.nlm.nih.gov/15534426/

"In humans, the coefficient of variation in the components of total daily energy expenditure is around 5-8% for resting metabolic rate."

That is nothing. That means the most extreme examples of this would be 200-300kcal. It's often just used as an excuse for a bad diet. And people believing in this myth is hindering them in making informed decisions.

[–] [email protected] 3 points 4 months ago* (last edited 4 months ago) (2 children)

5-8% is not nothing and it’s crazy that you would say that. (for reference, 200kcal is half of a nutrisystem frozen meal or an entire icecream sandwich.)

i encourage you to advocate for informed lifestyle choices, but if you mean that the coefficient of variation is 5-8% for resting metabolic rate, just say that, and don’t just open with “it isn’t even a thing in reality.”

[–] JeffreyOrange 4 points 4 months ago (1 children)

In my personal experience people judge it to be more like 25-100%. But I stand by 200kcal being nothing. It's not a make it or break it kind of difference. 200kcal more doesn't make someone obese or even fat. If you over eat by 200kcal a day it will take a long time to get fat and you will have years to intervene with a slight change that will fix it. And that would only be in the most extreme case. For most people we are talking about much less than 200kcal. If you have actually only a differnce of let's say 50kcal from the median and cite that as a reason for being over or underweight it's just wrong. But I have seen people use it as a reason so many times.

[–] [email protected] 5 points 4 months ago

Just to add to this, nutritional labels (in the US at least) can have up to a 20% margin of error, which is a much more significant source of uncertainty.