But after years of working with the fitness guru, who has also transformed the likes of Madonna, Nicole Richie, Kristin Davis and Kate Hudson, Gwyneth and Tracy have become business partners to help other women get the body they always dreamed of.
OKMagazine.com got to hang out with the business partners at the launch of their brand new fitness studio in Brentwood, California where Tracy dished on how best to get bikini ready during OK!'s 12 Week Countdown To Summer.
"Don’t believe any quick fixes because there aren’t any," the mother-of-two told us. "They aren’t sustainable. They don’t work. They actually cause your body’s metabolism and metabolic rate to get confused. So they cause much more harm than good."
"You know, your muscles are the one thing in your body that you can transform. Like don’t make them bigger than you want to. Compartmentalize them and make them strong to burn calories. So pick a program, hopefully mine, because I worked a really long time on it.
"You know you’re going to get the results that you want. Commit to it and before you know it, when you make it a lifestyle in one month you’re going to see changes, in a year you’re going to be a totally different person."
Gwyneth added that she soon realized that "there are no shortcuts" to getting the body you want but "consistency and discipline" is the way to go.
Tracy and Gwynnie's new flagship space has five studio rooms, VIP training rooms, on-site nutrition consultations and even a blow-dry bar to beautify yourself after your workout.
Meanwhile, new mom Molly Sims also gave her advice on getting bikini ready.
"Start looking in that mirror and I would say exfoliate. I would do a spray tan or some type of self-tan," Molly said. "That will really help. That will make you lose three pounds automatically for sure."
Who do you think has the best body in Hollywood? Weigh in below or tweet us @OKMagazine!