Metabolism was an excuse when we could not reliably estimate it outside laboratory; today we can do that too, for completely free (we run a public benefit app for this).
Method here: https://macrocodex.app/knowledge/rethink/adaptive-tdee/
People can find the algorithm here: https://macrocodex.app/knowledge/macrocodex/smart-calorie-bu...
In fact, our claim on the app is results within 2-5 weeks for both weight gain and weight loss; I've yet to find a guy who did not achieve success with this.
Calorie deficit is the most effective method for weight loss.
What's funny is when people actually measure their metabolism with this approach, they realize they aren't far off from the average!
I'm not quite sure why or how estimating metabolism helps here?
I mean, observing the weightloss / gain or lack thereof itself will tell you whether you need more of a calorie deficit or surplus. What does an independent metabolism estimate buy you?
The claim is usually that A) people have an inflexible appetite and will be increasingly driven to eat while at a caloric deficit, B) at some point this is almost involuntary and that point differs between people (e.g. consider not eating for three weeks; some people can do it on a hunger strike or a fast, but it really sucks), and C) some people have a slower metabolism which puts them under greater pressure to eat.
I don't disagree that calorie restriction is effective. I just think that you're dropping appetite from the equation when GLP-1 agonists have proven that reducing appetite is effective too.