The Oscar-winning actress turned to gym guru to the stars Tracy after she gave birth to her second child Moses seven years ago.
Tracy said the Sliding Doors star "had 35 extra pounds on her" at the time.
"Her butt was long and she had outer thigh problems," Tracy told Into The Gloss. "I felt so badly for her, and thought I could really help.
"So, I agreed, and she did everything I asked. Now, seven years later, she looks younger every year; she's totally transformed."
An Instagram photo of Gwyneth posted by one of her closest A-list friends Stella McCartney this week is sound proof that the mother-of-two really does look fabulous.
With her lean body and flawless skin, the 40-year-old understandably jumped for joy in the fun snap.
"Sexy lady in Stella swimwear!" fashion designer Stella captioned the photo. "Summer never stop! x Stella."
The sexy snake print two piece showed that Gwyneth's healthy and active lifestyle has clearly paid off.
Gwyneth is keen for others to adopt wholesome habits too. She released her second cookbook earlier this year. It's All Good promises to make you "look and feel great".
Avoiding gluten is one of the central tenets of Gwyneth's healthy eating philosophy.
Every single nutritionist, doctor and health-conscious person I have ever come across… seems to concur that (gluten) is tough on the system and many of us are at best intolerant of it, and at worst allergic to it," she says.
All of the recipes featured in the lifestyle guru's latest achievement are 'for the foods she eats when she wants to lose weight, look good , and feel more energetic', according to the blurb on Amazon.
But the American actress admits to indulging in guilty pleasures from time to time.
"I often have a glass of red wine in the evening and smoke a cigarette on a Saturday," she said "I love those moments because they are just the right amount of naughty.
"That balance keeps you vibrant. You have to live your life, after all."
Gwyneth started her own online lifestyle publication Goop in 2008 'to share all of life's positives', providing readers exclusive access to recipes and wellness tips as well as travel guides and fashion.