The star triumphed at last night`s Screen Actor`s Guild (SAG) Awards, picking up Best Supporting Actress for her role in `The Help`, but is worried her about her size.
She told People.com: "I am not healthy at this weight. Any time you have too much around the middle, then there is a problem.
"And when you reach a certain weight, you are less valuable."
But Octavia claims it isn`t just overweight actresses who have a problem getting roles in Hollywood, she also has a lot of sympathy with stars who are too thin.
She added: "I feel for the overly thin women as much as I do for the overweight women. It has to change.
"We have to start standing up for ourselves and saying, `This is who I am.`
"And If more women ate, they would be a lot happier. Let me tell you, I am a lot grumpier when I don`t eat."
Octavia also recently won a Golden Globe for her role in `The Help` - which tells the story of African-American maids who take a stand during the Civil Rights era in the US - although despite her two wins she doesn`t think she is a dead cert to claim an Oscar in February.
She added: "I would be lying if I didn`t say to you I would love to win an Oscar.
"But we have a group of brilliantly talented actresses, and it`s not a foregone conclusion that because I`ve won these awards then I`ll win [the Oscar].
"I would never be that presumptuous. I mean, Melissa McCarthy, Jessica Chastain and Janet McTeer are in that category. Pretty brilliant."