She said: "The first thing is for your doctor to tell you that you need to lose 18kg
"I got rid of soda and juice, that was the first thing I did. That literally was 9kg. right there."
The 48-year-old star admitted she found it tough to lose weight because she has a sweet tooth, but credited her 'Ghostbusters' co-star Kate McKinnon for inspiring her to do more exercise when they were on set together.
Speaking on 'Live With Kelly', she added: "Every time we went to dinner she would make me walk to dinner, we would walk after dinner.
"And then it just started becoming - I would work out, I would do yoga, I really tried to watch what I eat. It's not always easy because I do have a sweet tooth that's a killer. But I do they best that I can."