
Unsurprisingly, De Niro described "Raging Bull" as the toughest role he's had to prepare for during an appearance on The Hollywood Reporter's Actor Roundtable. According to Head Stuff, De Niro rocketed up to 215 pounds which resulted in the actor suffering from breathing difficulties.

This was during the period where production for "Raging Bull" moved from Los Angeles to New York, which is when De Niro was scheduled to shoot for "The Godfather Part II" in Italy (via CNN). De Niro did the same, and ended up gaining 60 pounds over the course of four months to achieve the desired goal.

But in La Motta's decline, the boxer gained a considerable amount of weight.
