from a medical term dictionary:
"Dowager's hump: An abnormal outward curvature of the vertebrae of upper back. Compression of the front (anterior) portion of the involved vertebrae leads to forward bending of the spine (kyphosis) and creates a hump at the upper back.
Dowager's hump is due to osteoporosis changes in the thoracic spine. It may affect men or women. Like most osteoporotic changes, it is often preventable."
So it is NOT fat and diet will not change it.
Treatments are listed here: en.wikipedia.org/wiki/Kyphosis