What causes Back Fat?
Basically, it is eating more in calories than working off in energy, really as with fat anywhere.
The body lays down all excess fat into fat stores to reconvert into energy when times are hard (part of our genetic make-up).
The problem is the fat that is laid down, sits in areas that are not easy to tone and this is the case with the back.
As you get older, of course, the tone of your muscles underneath shrivel, leaving the fat to sit and slide downwards. You're less active and your metabolism slows – but these are all issues that you can do something about.