The curvy actress insists she is not interested in dieting and would rather encourage young girls to have a healthy body image.
She said: "I am not a twig - and refuse to be a twig. I would like young girls who are screwed up about their bodies to think that it`s possible to have a healthy shape. Everyone gets a bit screwed up about themselves, physically, when you`re growing up.
"I don`t do crash diets or eat fish rather than meat and salads until they come out of my ears."
While she won`t diet, Kate does work out in order to stay healthy.
She told Reveal magazine: "I do exercise, with plenty of swimming, but never feel that I have the figure of a Hollywood actress."
The `Contagion` star also admitted she was a very "fat" child.
She recalled: "I was such a fat kid and reached 182lbs at one point. My sisters Anna and Beth would swap clothes but I couldn`t. I am the smallest at 5ft 6in and I`ve got my mum`s big feet and my dad`s round face."