Maintaining low bodyfat percentage is not unhealthy. However, there are methods of maintaining that low % that can be unhealthy. Correlation and causation are 2 different things.
It’s kind of similar to how for years scientists said “weightlifting stunts growth”… Yet there are still no real studies supporting this assertion or why it would be true. The assertion was made based on olympic weightlifters and gymnasts turning out much shorter than they were predicted to be as children.
However, steroid use has been proven to stunt growth (and olympians have a serious motivation to not be transparent and honest about this)…. So the mainstream media takes their word for it, and blames the exercises.
If you’re popping fat burning pills like candy, or starving yourself… THAT is unhealthy. Having low bodyfat % isn’t.
(Below 3% for men IS unhealthy…. but just to clarify 3% is where the skin on your stomach is about as thin as the skin on the back of your hand… It’s not very common, to say the least… And the phrase “low bodyfat percentage” would have to be changed to “EXTREMELY LOW” to mean 3% (average NBA players are 10-13%). Don’t worry about ever being 3% if you are eating a normal amount and not on performance enhancing drugs)