Restraint does have its pitfalls. When a man suddenly materialized during our interview to hand Ms. Kardashian West a large container from Pinkberry (and a plastic cup of sprinkles on the side), she was delighted. When she removed the lid and discovered her frozen yogurt was vanilla and not pineapple sorbet, she was deflated.

“Damn, that’s so annoying,” she said, more to her nearby chief marketing officer than to me. “I’m not going to waste my calories if it’s not perfect.” Texts were sent, and the unseen man — or someone, perhaps another man — was dispatched back to Pinkberry. “If it’s not delish, it’s not worth it.”

Ms. Kardashian West’s diet and body image, like many things in her life, has always been an open book. When she was trying to lose weight after childbirth, she used to post photos of her scale on social media.

Skims’ most recent product drop is her signature waist trainer in a new nude color. (A waist trainer is a corset that “sculpts you perfectly to accentuate your body’s natural curves,” according to Skims, but also “crams all of your organs together,” according to an Atlanta physician.) The Kardashians have long evangelized waist trainers, wearing them at the gym or, especially, while relaxing at home.

This is how Ms. Kardashian West will get to a billion dollars, if she does indeed get to a billion dollars: by convincing people of the radical idea that shapewear is casualwear and loungewear, too, when its domain has previously been first dates and party outfits. The logic used to be that shapewear was like armor — supportive protection for moments when you may feel exposed. But now everyone is exposed, all the time.

Ms. Kardashian West said it makes her happy to FaceTime with her sisters when they’re at home and to see they’re wearing Skims, “you know, not for a photo,” she said. “It’s genuinely the most comfortable thing for them.”

“I feel better when I’m wearing shapewear,” she said. “That’s just me.”