The actress revealed that intimate scenes for her new series The Client List will force her to forgo some of her favourite foods in order to stay slim and look good in her underwear.
"I will be in lingerie a lot, so I'll be working out," Hewitt explained to People.
"I will not be eating for the holidays. This year will be loads of fun for me."
Earlier this year, Hewitt signed on to star in the big-screen adaptation of Broadway's Jewtopia.
In August, Hewitt was forced to deny rumours that she was romantically involved with former Bachelorette contestant Ben Flajnik.