Jennifer Aniston shows off her tight tummy in a new ad for Smart Water.

“Working out feels great…afterwards,” the ad’s copy reads. “That’s why I drink Smart. It’s hydration I can feel. (And it’s one part of my routine I never sweat.)”

Jen has denied being put on the baby food diet by Gwyneth’s trainer, Tracy Anderson.

“Sorry, but the last time I had baby food, I believe I was 1,” she told People. “I’ve been on solids for about 40 years now.”