Revenge Body with Khloé Kardashian trainer Lacey Stone says a mental transformation is necessary for any physical changes to stick

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Having made a transformative journey of her own, celebrity trainer Lacey Stone was thrilled to participate in Khloé Kardashian’s total transformation reality show Revenge Body.

“I created a program called 8 Weeks to Change, which is a transformative program taking people from their lowest point to their highest point, and I created the program through a hard time in my life,” Stone tells PEOPLE. “I’ve been divorced, I’m gay, I’ve struggled with transferring from New York to L.A.”

Stone joins some of Hollywood’s other top trainers on the show to help people achieve full body makeovers — which Stone says begins on the inside.

“Fitness starts in the mind, not the body,” she says. “The mental component is the most important. If a person isn’t motivated outside of something superficial, they’re not going to follow through.”

Stone says she tries to hone in on larger issues that may be blocking someone from reaching their full potential.

“I get to the root of what’s stopping them, and every day we come up with strategies to address that, and substitute what they would normally do with something more positive,” she says.

In addition to the mental aspect, Stone puts her clients on a healthy diet plan and rigorous exercise regimen.

“I put them all on a food program called Klean L.A. It’s perfectly portioned meals, organic, healthy, delivered right to your door,” says Stone. “In each meal there is a palm-sized protein — eggs, chicken, fish or red meat. The majority is vegetables, plus a very small amount of carbohydrates, because you do need carbs with the style of workout that I have. The problem in America is portion sizes — people eat way too much or way too little.”

WATCH: Khloé Kardashian Slams Critics over Weight Loss: ‘First I’m Too Fat and Now I’m Too Skinny’

Stone admits that her workouts are “not for everybody!”

“I am going to push you to your limit,” she says. “You work out two days a week one-on-one with me or my team doing an athletic-inspired, full-body, strength training-meets-dance class. Then during the week, we do two or three Flywheel classes. It’s different than any other indoor cycling class in that there’s technology to monitor every pedal stroke so you can see that you’re getting better every class, which creates a sense to work harder to get better results.”

Stone says working with Kardashian on the show has been “really inspiring.”

“She took this really negative thing in her life — she’s been made fun of for being the ‘overweight’ Kardashian — and she was like, enough,” says Stone. “She worked really hard to be the version of who she is now, and she’s really happy, and you can see it. Because of her, 16 people’s lives have completely changed, so I think she deserves a lot of credit.”

For anyone looking to start their own transformation journey, Stone offers some no-B.S. advice.

“Stop whining, stop the excuses,” she says. “Look in the mirror and ask, ‘Are you happy?’ because if the answer’s no, then let’s do something about it.”

Revenge Body with Khloé Kardashian premieres Jan. 12 on E!