No. It can't be.
Working out at the gym has health benefits. One of it would be to get a muscular and aesthetic chest. And for the same reason, it is hoped that lifting weights would help get rid of the excess breast tissue. The reason why it does not help has to do with the tissues which are responsible for gynecomastia.
Gynecomastia is comprised of glandular tissue, surrounded by varying amounts of fat. The muscle which gives definition to the chest is pectoralis major and is found behind the breast tissue. Working out at the gym and lifting weights can augment the size of the muscles. This can lead to a more anterior (forward) position of the overlying breast tissue. So paradoxically, lifting weights can make the deformity more obvious.
Losing weight can have beneficial effects on the appearance of gynecomastia. This acts by reduction of the fatty tissue. This will lead to an overall reduction in the size of the breast tissue. However, losing weight does not reduce the glandular tissue found beneath the nipple-areola. So there would be a persistence of the puffiness of the nipple region.
So what gets rid of gynecomastia?
In most cases, the answer would be surgery. Due to technical refinements, it is possible to treat this condition with very small incisions. Fat around the gland is treated with liposuction and the gland is removed with a small incision in the areola (the dark skin surrounding the nipple). In most individuals, these lead to very fine scars. The goal of gynecomastia correction is improved aesthetics of the chest. There is a role for medical intervention in cases of gynecomastia which are secondary to abnormal levels of certain hormones.
To conclude, cosmetic surgery offers a definitive cure for this condition which can't be attained by pumping weights at the gym. Otherwise, bodybuilders would have been immune to this condition.
For more information about gynecomastia, click here.
I like to keep it simple.