Elizabeth Moss, Christina Hendricks and January JonesCurves are so in on 'Mad Men' that some actresses from the show have been warned to stay away from the gym.

StyleList reports that January Jones -- who plays troubled housewife Betty Draper on the hit AMC series -- tells the new issue of Tatler magazine that 'Mad Men' creator Matthew Weiner has warned her and fellow castmates Christina Hendricks and Elisabeth Moss to avoid hitting the gym so they'll stay curvy.

"He would prefer we didn't work out and that we eat really well, so we look like healthy women," says the 32-year-old blonde beauty, who was scolded last year for being too thin, according to the newspaper.

Jones, who admits that she loves beer and carbs, is happy to follow Weiner's orders, especially because she's sending the message to 'Mad Men' viewers that "it's OK to have curves and be a woman," she explains. "I wish more women would realize that's what men like."

Another benefit of carrying a few extra pounds: the sexy hourglass silhouette Jones gets from the girdle she wears for the show. Says the star, "It gives you such a nice shape."