The former 'Coronation Street' actress, who ties the knot in a fortnight, said losing the weight meant she put off buying her wedding dress.
She told Hello! Magazine: "I am the complete opposite of people who start trying on wedding dresses the day after the proposal. One of my bridesmaids, the actress Angie Lonsdale, was nearly sick at the thought that I hadn't sorted my dress".
She will be given away by her father Vin, and her youngest son Louis, 12, will be an usher at the ceremony in Portugal.
The 55-year-old said she is not worried about the age difference with her fiance, 40-year-old Lincoln Townley.
She said: "We are going to grow old together, it's just I'll be quicker at it."
"I hadn't been that weight since I was pregnant. It wasn't about trying to become stick thin or reaching a certain size. I just knew it was unhealthy for me to be so big. I know 11 stone 5 isn't obese but for me, who should be around nine and a half stone, it was," she said.
The star said giving up alcohol was easier because she and Lincoln did it as a couple.
She said: "We've said we couldn't have done it without one another, we were each other's anchor."
And the couple will not be tempted to raise a glass at their wedding.
Welch said: "Do you think if we could have two drinks that we wouldn't have two drinks?
"I love the thought of having a gin and tonic. We'd love the thought of sitting with a beautiful bottle of red wine between us and then let it go. It wouldn't. It might for a while but it would escalate.
"We'd be millionaires if we had money for every time people have said to us 'but you'll have a drink at your wedding won't you?' We don't drink."
Read the full interview in the latest edition of Hello! Magazine, out now.
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