On tonight's episode of the new, groundbreaking A&E series "Fit to Fat to Fit," personal trainer Carrie Cox leaves her healthy lifestyle behind as she sets out on a mission to gain as much weight as she possibly can in a span of four months, just so she could lose it all alongside her new client, Kenlee.

The series pushes personal trainers outside of their comfort zones and places them in their clients' shoes. By gaining weight, each of the trainers learn the struggle each of their clients face as they adopt new, healthier eating habits and take on difficult fitness routines first-hand, because they're right alongside them for the journey. Tonight's episode features Cox, a 27-year-old gym owner who aims to inspire women.

"Health is the experience you live each day," Cox writes in her biography. "How much you can bench press has nothing to do with it. It took me 25 years to learn how to receive love-and how to give it."

"My life has been blessed by incredible women," she continues. "Teaching them to love and to give themselves some slack. To nurture and cherish the experience we call life."

Cox's client Kenlee is a wife and mom who struggles with making healthy eating choices and finding time to work out with her busy lifestyle. Cox aims to gain as much weight as she possibly can so she can lose it along with Kenlee.

"This is amazing," Cox says in a sneak peek for tonight's episode, as she adds more whipped cream to a milkshake.

"Hopefully you turn into back fat," she says as she stares down at a table full of pastries.

The rest of the clip cuts to Carrie as she consumes a giant cheeseburger, pizza and other high-calorie foods, then cuts to a clip of the trainer sharing a bottle of green juice with her client, post-workout.

"I'm willing to sacrifice my body because it's about empathizing with somebody really struggling emotionally," she says.

But Cox begins her own struggle to get back into shape, and she holds her hand over her face as she breaks down, sobbing.

Watch the full sneak peek below and be sure to catch the next episode of "Fit to Fat to Fit," airing Tuesday at 10 p.m. EST on A&E.