How Jessica Simpson Lost 100 Pounds By Working Out Only 3 Hours a Week (Exclusive)

The businesswoman's trainer is sharing how she shed the weight!

Jessica's Simpson's trainer is sharing how she bounced back in shape after welcoming her third child.

A little over six months ago, Simpson's daughter, Birdie, arrived. Since, she's lost 100 pounds and has been showing off her new figure on social media. So, how exactly did the singer-turner-businesswoman manage to shed the weight? ET's Nischelle Turner spoke with trainer, Harley Pasternak, to get some answers.

"She lost the weight because of everything she did when she wasn't in the gym. Of the 168 hours of the week, she's only working out around three of those," he revealed. 

This begs another question: What was the 39-year-old doing outside of the gym that helped her lose the pounds? Walking 12,000 steps a day!

"After she gave birth, we kind of had to work up to that," Pasternak said. "We went from four, to six, eight, ten and then to twelve. And there are some days she knocks out fourteen." 

However, he said that some lifestyle choices also had to change in order for Simpson to get the results she wanted. Besides walking 12,000 steps a day, she also got better-quality sleep and, perhaps hardest of all, did away with all sugar.

For people who struggle to give up sugar, Pasternak has co-created a product to help ease the transition to healthier habits. His Sweetkick mints are designed to assist people in managing their sugar cravings and maintain their diets.

Pasternak also shared a policy he has: "I don't believe in a 'cheat day' but I believe in 'free meals.' So, two 'free meals' a week. Do them on different days, the same day, it's up to you."

Simpson hopped on Instagram in September to post photos of her svelte figure, writing beside: "6 months. 100 pounds down (Yes, I tipped the scales at 240 ?) My first trip away from #BIRDIEMAE and emotional for many reasons, but so proud to feel like myself again. Even when it felt impossible, I chose to work harder. ?."

After revealing her weight loss, Simpson appeared on HSN, where she shared that she's eaten a whole lot of one item ever since her pregnancy.

"It's been a lot of hard work. I have to say that I have worked very hard," Simpson said. "Everything that I've been eating is mostly made with cauliflower. "

She also shared a piece of advice that helped her stay accountable as she worked to shed her pregnancy weight.

"I don't like the word 'diet.' I just ate a bag of Cheetos in the back," she shared. "I do think that writing down what we eat is important to keep ourself in check." 

Check out ET's full chat was Pasternak above.