Fat promotes the conversion of some of the free testosterone to Estrogen,
and that's the main reason for gynecomastia.
It usually happens in early puberty when T levels have not yet fully ramped up,
thus the resulting to T to E ratio resulting from T conversion is is low.
Higher T to E levels later in puberty lessens the impact of E and most often
the small breasts dissapears.
In some with susceptibility to E, they don't disapeer.
If you have substantial obesity, they also won't disapeer.
If your substially fat, the T to E level from the testes ouput is still not
enough to suppress estrogen's action on the receptor and fat accumulation
in female areas occur. Thighs, breasts, buttocks. The problem is once
there, those fats are very hard to get rid of unless E levels go down,
but they can't go down unless you lose mucho weight. Its a vicious
circle.
One solution is to build the muscle mass to increase metabolism and T.
