> Losing weight without losing muscle mass is very hard.

Yes it is.

> It requires extreme diets like a protein sparring modified fast where 80%+ of your calories are from lean protein while running a 50% caloric deficit.

I’m not any sort of expert but that sounds frankly, dangerous. I don’t see how you do something like that without damaging your liver.

It’s very possible to lose weight and gain muscle, but you have to be at just the right body composition (not lean and not obese) and then there’s a question of “over what period of time”?

Any duration under a month is probably pointless to measure unless you have some special equipment. Any duration over a month and it’s kind of obvious that it is possible. Eat a balanced diet without junk, work out regularly, and keep the calories to only what is necessary.

> I’m not any sort of expert but that sounds frankly, dangerous. I don’t see how you do something like that without damaging your liver.

I haven’t seen any credible research that a healthy person can damage their liver from excessive protein intake. Someone suffering from liver disease needs to be careful, sure, but evidence that it would harm a healthy liver is practically nonexistent.

That said, PSMF is explicitly not a sustainable diet and proponents generally don’t claim it to be. It’s a short term diet meant to preserve muscle mass under extreme caloric restriction (under 1.2k calories).

> Eat a balanced diet without junk, work out regularly, and keep the calories to only what is necessary.

If it were as simple as that, we wouldn’t be having this conversation.