Not a fitness expert, but from what I know (spmeone crrect me)

Body builders aren't inherently strong. I mean, sure they are but all they mostly train for muscle definition, not strenght.

That's why you see jacked up body builders with tree trunks for arms lose an arm-wrestling contest against professional arm-wrestlers.

https://youtu.be/AAmCxXDkcdI?t=42s

Someone who trained for a very specific situation (in this case, Rousey on fighting) would be able to overcome the "supposed" physical superiority of the body builder.

That said, male physiology should still come into play. So, he would most likely win. 55 pounds is no joke, especially since they're of different genders.

If this was a hulking female body builder vs Rhonda Rousey though, my money would be on the latter.