The 46-year-old This Morning presenter – who is a UK size 28 – said she is happy and comfortable with her body shape, but that the embarrassing moment in 2007 made her resort to weight-loss surgery.
Hammond writes in her new book You’ve Got To Laugh, serialised in The Sun, how she noticed when sitting down to interview Damon for the third Bourne film The Bourne Ultimatum that her chair felt a bit tight.
She goes on: "I was interviewing Matt! What can I say? Hottie! Fittie! He was incredible. I was so pleased to meet him. But halfway through the interview, something awful and embarrassing happened.
"My size and weight went against me and suddenly the side of the chair broke. It was a horrible, shameful moment. My girth had broken the chair while I was interviewing Matt Damon, one of my idols! I was mortified. I wanted the world to swallow me."
She said the 50-year-old actor was very "nice" and asked if she was OK and offered to get her another chair.
She revealed she told him: "'Don’t worry about it,' and I ripped the arm off the chair and flung it on to the floor. That made him laugh and, instead of bursting into tears, which would have been the natural thing to do, I started laughing as well and we carried on with the interview."
But despite laughing it off, Hammond admitted she felt "mortified" and asked for the incident to not be aired on TV.
She revealed that afterwards she decided: "I’m having a gastric band. I didn’t want to be fat any more."
Hammond had the operation later that year but had the surgical procedure reversed two years later after her body rejected it, causing her to suffer regular vomiting.
The former Strictly Come Dancing contestant admitted she is actually very happy with her body the way that it is.
She said: "I’m beautiful and a lovely person, and I know it. I’m not one of those people that hates myself. I actually love myself."
Hammond found fame on the third series of Big Brother in 2002 before launching a successful TV career.
As well as being a presenter and guest host on This Morning, she has appeared on numerous reality shows including I'm A Celebrity... Get Me Out Of Here!, The Great Stand Up To Cancer Bake Off and Celebs Go Dating.
Watch: Alison Hammond's hilarious Trick Or Treat confession