Hillary Swank used to be a vegetarian, but she had to gorge on fish to prepare for her role of a female fighter in the movie 'Million Dollar Baby', which left her body riddled with mercury poisoning.
The double-Oscar winner, 36, needed a protein-packed diet to build up her strength during filming of the 2004 movie.
So she began devouring huge quantities of fish, leaving her with dangerously high levels of mercury in her blood.
After struggling to get her body back on track, Swank was forced to go back to her vegetarian diet.
"I put on 19 pounds of muscle: I was 29, I was a vegetarian and suddenly I was eating so much fish that I got elevated mercury problems," the Daily Star quoted her as telling You magazine.
"It plagued me for a couple of years after that movie. When I discovered that my health was suffering, I had to change my diet. So now I eat pork and beef."