sorry, but that's bullshit.
6 pack is visible at about 15% of body fat and below, which is about the recommended amount.
going lower than that doesn't have any negative effects either, its just that someone who is under 10% and not fit has other problems related to under eating.
PS: woman numbers are not different because they would be allowed to have more general fat, just boobs and ass has quite some of additional fat.
![](http://www.weightlossresources.co.uk/img/b/bodyfatb.jpg)