Credit: MB/; Kevin Mazur/

Is Zac Efron trying to slim down?

On Thursday, the actor, 23, visited an L.A. studio (he's doing voiceover work for a new Dr. Seuss flick) with a bag of grub from Z.E.N. (Zero Effort Nutrition) foods, a diet delivery service that helps stars eat calorie-controlled meals.

Efron has said he gained about 18 pounds (and got a much-scrutinzed buzz cut) to play an Iraq War veteran in The Lucky One.

"I was just eating, eating, eating," he told E! News of the beef-up. The Lucky One wrapped up shooting just before Christmas.

Another Z.E.N. Foods afficianado? His ex Vanessa Hudgens. "I'm so thankful there's a service like Z.E.N. Foods that tastes GREAT and makes it so easy to eat right," she says on the company's website.

Although the pair called it quits after almost five years in December, they were spotted packing on the PDA at L.A. nightclub Eden earlier this month.