"It was really painful, and I had to go to a rheumatologist who put me on a steroid. I was freaking out. I cut out the meat again, and it's calmed down."
The Skims owner admitted her preparations for the Met Gala were a "rollercoaster of emotions" because after finding the famous gown - which was worn by Monroe in 1962 when she sang Happy Birthday to then-President John F Kennedy - she wasn't sure she'd be able to wear it because of its small size, while everyone around her was concerned about it getting damaged.
She told Allure magazine: "It was a roller coaster of emotions.
"To even find the dress was a feat, and then to get them to allow me to wear the dress was another feat. You have [to wear] gloves and there are guards and you had to put down special paper. I think [the dresser] was shaking because if anything rips, if anything goes wrong, you know? This is Marilyn's dress. And it absolutely did not fit.
"Two weeks before [the Met Gala], I was 10 pounds (4.5kg) down and I was so proud of myself. Then I got down 15 [pounds] (6.8kg) and it fit. I couldn't believe it."
The 41-year-old beauty - who has four children with ex-husband Kanye West - faced criticism over her extreme weight loss but she thinks the backlash was unfair.
"If I was starving and doing it really unhealthy, I would say that, of course, that's not a good message. But I had a nutritionist, I had a trainer. I have never drunk more water in my life," she said.
"I don't see the criticism for other people when they lost weight for roles — they are [considered] geniuses for their craft.
"There are so many things out there that are so not accurate and not true."
