Senior foods have less protein in it and older dogs need less protein, so I am told anyway unless all I read is a scam as well, wouldn't be surprised though if it was?
Susie is nearly 16 now and I buy her senior but not all the time, depends what is on offer, she is not fat so I am not worried about that aspect.
I know that tinned food makes her fart a lot, worse than my hubby!!!!! phew!!!!