It is definitely possible i got him to almost lose but was short by 5 hit points. One tip I have is to use all of your +2 fitness cards in your deck he has cards that go through fitness but it takes him a longer time to get those cards also pay close attention to how many cards he has left and how many he has in his hand. I was right my deck defeated him I had 51/54 left and he was knocked out you get the it's all muscle card once you beat him
To add to this, be sure to add the fitness card from your previous fight! Costs 1 less and can add 1 more muscle with full hand than the normal fitness cards.
The guy is beatable and worth the try! You have to toy a bit with your deck building and use certain game mechanics to their fullest. It would also help to save weight from previous fights.
Oh, and for anyone interested in seeing more, try to lose a certain fight...