I think it is especially awkward for men, sometimes, to give a compliment to a woman about her appearance.
I had some male coworkers make the same comment to me. I just laughed and said, "Well I can assure you, there's no immediate danger of THAT!!!"
One, who I have worked iwth for quite some time, was more direct but still said, "It's really politically incorrect to say this, but have you lost some weight?"
Bear in mind, I didn't share the details of having surgery with my co workers.