I agree with Greytness. And yeah, it may well be hormones. Yours may be going through puberty. Be careful how you handle and touch your guy/gal in case it's hormones -- you don't want to make things worse!
That said, Greys can suddenly refuse a favorite food -- mine has mostly gone off grapes.
But with the info you shared - I suspect it is nothing serious. Hormones may well explain it all -- esp if the regurgitating is a new thing. I would expect (with new puberty/hormones) he/she may suddenly develop a close relationship to a favorite toy, or the other parrot, or to you. Hence my advice to be careful in how you handle or touch him/her.
[Greys are complex creatures -- you may never know why the diet has changed. Keep offering healthy foods! The main thing is keeping an eye on your guy/gal, making sure there is no weight loss or signs/symptoms of illness. I mean, if things continue and he's actually losing weight, another vet visit may be called for. But I'd guess it's probably just puberty/hormonal changes.