In her new memoir, Open Book, the 39-year-old singer recalls a particular low point in her decades-long struggle with body image. This came in 2015 after she had given birth to two of her three children -- Maxwell, 7, and Ace, 6 -- with her husband, Eric Johnson. The couple has since welcomed a daughter, 10-month-old Birdie.
"I was so ashamed of my body at this point that I wouldn’t let Eric see me without a white T-shirt on," Simpson writes. "I had sex with it on and even showered with it on. I couldn’t bear to look at myself."
Because of this, Simpson decided to get a partial tummy tuck. In a recent interview with ET, which will air in full during Tuesday night's episode of Entertainment Tonight, Simpson opens up about her decision.
"That was after I lost a ton of weight and I had skin and stretch marks because I had two babies back-to-back, 14 months apart," she said, adding that she had "gained so much weight" during her pregnancies.
Despite her want for a tummy tuck, that plan was initially shot down by her doctor, who was concerned over her liver levels. Simpson's levels were high at the time due to her alcohol consumption, so much so that the doctor said to her, "You could die."
"I told Eric. We were in a sort of shared spiral, both of us in denial about how much we were drinking," she writes of telling her husband of the doctor's comment. "I’m sure we were wasted when we talked about it."
Despite the medical warning, Simpson decided to go ahead with the procedure, even opting to undergo a second, more intensive surgery when she wasn't happy with the first results.
"There was a sense that something was going to go wrong from the get-go, even though I stopped drinking to prepare," she writes. "The day of the surgery, Eric was puking his guts out because he was so nervous."
"The surgery took two hours longer than planned… It did not go well," she continues. "I got an infection -- colitis -- and was vomiting so much I thought I was going to bust my sutures. My mom and Eric were so worried. They had to rush me to Cedars, and I secretly stayed there for nine days. Doctors talked seriously about me needing a blood transfusion."
The experience, she writes, was "so hard on Eric, who was convinced he should have talked me out of going through with the surgery."
"Eric loved me at any size or shape, even if I couldn’t," she adds.
The tummy tucks were one in a long line of things Simpson had done to alter her body since she was told to lose 10 to 15 pounds when she was 17 years old. At the time, Simpson writes that she "immediately went on an extremely sick diet, and started taking diet pills," the latter of which she would continue for "the next 20 years."
As her fame rose, Simpson was encouraged to show more and more skin, told to get "Janet Jackson abs," and given a trainer. The pressure got so great at one point that she "would draw a six-pack" on herself with an eye shadow pencil.
She later started the Atkins diet. "Off the diet, I obsessed over how I looked 24/7; on the diet, I was also hyper focused on food. It made me nervous," she writes. "My anxiety had something to hold on to, and instead of examining my emotions, I could just block them out by focusing on carb counts and waist sizes. If I focused on controlling my outward appearance, I could avoid thinking about my emotions and fears."
Within a few years, she was down to 103 pounds. "Everyone went on about how great I looked, but I couldn’t enjoy it because I was so freaking hungry," she writes. "When I ate anything, I yelled at myself, asking why I was getting in my own way and why I hadn’t gone to the gym."
She went on to up her dosage of diet pills ahead of her 2002 wedding to Nick Lachey, before getting in the "best shape of my life" to play Daisy Duke in The Dukes of Hazzard a few years later.
"I saw Daisy Duke on the screen, and then just the teeny tiniest stomach shadow of Jessica," she writes. "I was in the best shape of my life, and I didn’t appreciate it, but also it just shows the absurdity of how we always find something to criticize about ourselves."
A few years later, Simpson's body was in the spotlight again, this time when she performed in a sleeveless black bodysuit top, high-waisted blue jeans, and a Fendi leopard-print belt, an outfit that "started a decade-long international discussion about my body" and made "a dysmorphia set in."
"I had created a gold-standard Jessica, the 'before' for every 'Is she fat or is she thin?' story for the rest of my career," Simpson writes of the result of starring as Daisy Duke. "The fact that I was that skinny and that I was deemed overweight still frightens me."
Open Book is available now. Tune in to Tuesday's episode of Entertainment Tonight to watch ET's full interview with Simpson, as she discusses body image and her memoir's other reveals.