Josh Hartnett Shares Matt Damon's Weight Advice During 'Oppenheimer' Filming

Hartnett reveals Damon warned him about the challenges of losing weight gained for roles, especially over 40.

Hartnett gained 30 pounds to play Ernest Lawrence in 'Oppenheimer'.
Damon repeatedly advised against weight gain for roles, citing his own experiences.
Damon's rapid weight loss for 'Courage Under Fire' led to health issues.
'Oppenheimer' won seven Academy Awards, including Best Picture and Best Director.
Hartnett is promoting his new film 'Trap', directed by M. Night Shyamalan.