> Losing muscle as you lose weight is natural and good.
It's natural but that doesn't make it good. In particular, muscle loss can cause heart problems because the heart is a muscle. The body's catabolic processes don't distinguish between different kinds of muscle.
I don’t think this is true. My understanding is that the heart is a very unique muscle because it doesn’t grow. If your heart does grow, either by genetic defect or anabolic abuse, it works much worse. So you’ll live a shorter life.
Heart muscle can shrink in extreme calorie deficits which can lead to heart issues, therefore it must grow when leaving such calorie deficits, even if that growth has an upper bound.
It's natural but that doesn't make it good. In particular, muscle loss can cause heart problems because the heart is a muscle. The body's catabolic processes don't distinguish between different kinds of muscle.