Fans have wondered for years how Jennifer Aniston keeps her stunning figure. Well, wait no longer, as Aniston’s fitness instructor has revealed the secrets to her slim physique.

Mandy Ingber, the former Friends star’s instructor, explains that Aniston stays in amazing shape all of the time, however when she has a few secrets for when she needs to tighten up quickly.

“Jen’s a very consistent exerciser and eater,” Ingber explained to ABC News. “But when she has something she needs to focus a little more on, she just tightens it up a little bit.”

Aniston and her fiancé Justin Theroux recently jetted off for a vacation in Bora Bora to celebrate their two-year anniversary and Theroux’s 43rd birthday. Aniston wanted to tune up her look so she just turned to her self-discipline. “She won’t have the extra chips,” Ingber said. “It’s kind of like just being disciplined, she’s like anyone else that she goes through those times when she can lose a little but pretty much, she’s always in great shape.”

Ingber also revealed that Aniston turns up the cardio when she is needing to tone up quickly. “We up the cardio a little bit, if she’s looking to sort of trim down,” Ingber added. “So we add a little more cardio to the yoga, but also what she puts into her body is essential. That really is 80 percent of it … it’s not a big deal if you have a bite of this or that if you are mostly eating well.”

So, what is Aniston most worried about when it comes to her body? According to Ingber, it’s her bottom. “She focuses on butt exercises for sure, I’ll add some squats into the yoga routine,” Ingber said. “For me, there’s no better thing to lift your butt than squats. Pretty much, that’s gonna do it … she likes to focus on that like most women. Most of us want that area a little higher.”