The Notebook star recently told Glamour magazine she had to abandon her meat-free diet because it wasn't giving her the energy she needed to get through the day.
She says, "It made me very tired. I just ate pasta - I was the most unhealthy vegetarian ever! I'd like to try it again now that I know about (popular meat alternatives) quinoa and bulgur. I think I'd be better the second time around."
And PETA bosses want to help her give up meat for good - they have sent McAdams cookbooks The Conscious Cook and The Kind Diet, together with "a vegetarian starter kit and other fun goodies".
A spokeswoman for the organisation tells WENN, "I hope it can be a nice re-introduction for her to do veggie the right way."