That is just not naturally possible, not at all. 80Ibs of muscle is HUGE amount. You wouldn't get that in 5 years of hardcore workouts & nutrition.
Bale also didn't look like he was on steriods. More reastically he probably gained 8–10Ibs of muscle.
Damn, I don't remeber that at all. Though I haven't read it since the 90's.
Actually it is possible. He filmed 'The Machinist' while weighing 120lbs after a weight loss of 63lbs for the role.
He had 5 months after filming finished at that 120lbs to get up to the 220lb weight required for Batman Begins.
You don't have to take my word for it:
Christian Bale's physique in this Batman revamp may not be the most spectacular on the list, but consider this — six months before playing the caped crusader, Bale weighed 120 pounds. Taking a page out of Robert De Niro's playbook, the Welsh actor had dropped over 60 pounds (mostly through a steady diet of coffee and apples) for his role as an emaciated insomniac in the psychological thriller The Machinist. When he landed the lead in Batman Begins, Bale only had half a year to get in shape. Wasting no time, Bale started a high protein diet while utilizing heavy core training, plyometrics and resistance training. By the time cameras were ready to roll, Bale had packed on 100 solid pounds. Ironically, director Christopher Nolan felt Bale had gotten too bulky and ordered him to drop 20 pounds.
Due to his part in The Machinist (aka The Machinist), Christian Bale was vastly underweight (about 120 pounds on his 6 foot+ frame) when he was under consideration for the part. After being cast, he was told to become as "big as you could be" by Christopher Nolan. Bale underwent a dietary and exercise regimen and ending up weighing about 220 pounds