JENNIFER Aniston says smiling keeps her slim. The actress — who’s set to marry Justin Theroux sometime this year — has learned that dieting is no longer important to keep trim, and instead likes to spend time in the sun with a big grin on her face. “I stopped dieting when I figured out that you just have to ear regularly and properly within moderation,” she said. “The fads are too much. I think it’s really about — honestly, this is going to sound silly — going in the sun for 20 minutes a day is really important, vitamin D, because we are now having a vitamin D deficiency because of all the SPF.               –SS