Joaquin Phoenix has long had a reputation for method acting, but his work for “Joker” has taken the job to a new extreme. The actor reportedly lost 52 pounds to play the title character, which he said did a lot more than give him a disturbing gaunt look — it also derailed his mental health.
https://www.insider.com/joaquin-phoenix-joker-weight-loss-eating-disorder-symptoms2019-10

