Jennifer Aniston took a break from filming The Bounty on Aug. 22 to enjoy a meal with co-star Gerard Butler and some pals at Freemans eatery on NYC's Lower East Side. Instead of nibbling on a salad, "she shared her dessert with her table and drank with her friends," an onlooker tells Life & Style. "She's tiny, but she looks strong and healthy. Her arms were amazing, she was in great shape and she looked comfortable in her own skin."

It's no wonder Jen seems so confident and flirtatious -- her toned curves, tight abs and perky assets are looking better than ever. "I feel more comfortable today than I ever did in my 20s or early 30s," Jen, who turned the big 4-0 in February, recently said. Part of that newfound serenity comes from incorporating fitness and food into her life -- instead of making them the enemy.

"Whenever she wants to look her best, Jen does this strict diet so she's able to lose 5 pounds in five days," an insider on the set of The Baster (a comedy Jen filmed with Jason Bateman before The Bounty) tells Life & Style."She did it during her past few films and doesn't find it hard at all. I saw her eat pasta only once!" But the yoga devotee -- who flew her instructor, Mandy Ingber, from LA to her NYC set -- always eats enough to keep up her energy. "She routinely gets up at 5 in the morning to run before filming starts," says the insider, who was on set with Jen as she filmed The Bounty at Monmouth Park race track in Oceanport, N.J., on Aug. 17. "We were filming from 6 a.m. until almost 11 at night, and she had a great energy level the whole time. She was upbeat and smiley and never flubbed a line -- and her body looks amazing!"

To read more on Jen's on-set diet tricks, pick up this week's issue of Life & Style, on newsstands now!