In order to get that ridiculously cut look, Hugh Jackman's routine involves intentionally dehydrating himself for several days before filming a shirtless scene, which is stupidly dangerous for a silly little superhero movie (or anything else), but it does make a difference: compare Wolverine in The Wolverine (where he first used the technique) to Wolverine in X-Men: Apocalypse (where the size of the cameo didn't warrant it), and you can see what expunging all the water from your body does.
Of course, the part you can't see is the strain that would put on your kidneys or the fact he's always constantly dizzy while trying to deliver lines and perform stunts.
