Britain's Sarah Ferguson felt like she was "drowning in food" before she lost 42lbs.
The Duchess of York decided to drop the extra pounds after realising she was close to the weight she was when she was heavily pregnant with her first child Princess Beatrice 25 years ago.
She told HELLO! magazine: "Beatrice was an 8lb 8oz baby and I was only 6lb off my full-blown pregnancy weight. I decided to make a change. I used to be so angry - I believed that I had lost control. I couldn't fit into any of my clothes.
"I was just drowning in eating, drowning in food. It took courage to go out in public in all the years I have been overweight."
The 54-year-old royal - who was 224 pounds at her heaviest - took part in a gruelling daily boot camp session on a Swiss mountain resort, and managed to drop the weight in just five months.
She has also cut out sugar and maintained a healthy diet.
Meanwhile, the flame-haired beauty - who was once an ambassador for Weight Watchers - has become an official envoy for the Institute of Global Health Innovation at Imperial College London.
She said: "I want to help combat obesity."

George Michael thinks Britain's Duchess Catherine is "stronger" than the late Princess Diana.
The 50-year-old singer believes Catherine, 32, will be able to deal with the "lunacy" of fame better than her husband Prince William's mother, who died in a car crash in France in 1997.
George - who was friends with Diana - said: "I think Diana would have been incredibly happy for William and Kate.
"And I think she'd also be really, really pleased that William has met and fallen in love with someone who has the strength of character to be able to deal with the sorts of things that she couldn't."
The 'I Can't Make You Love Me' hitmaker sympathises with the royal couple - who got married in 2011 - as he understands what it's like to be judged on a daily basis and admits it almost sent him mad.
He explained to the Daily Star newspaper: "I do know just how challenging and exacting that level of fame can be.
"It's like living in a goldfish bowl. Sometimes, especially during the Faith years, I felt close to lunacy."
Meanwhile, Prince William and Duchess Catherine - who was known as Kate Middleton before she married William three years ago - now have an eight-month-old son Prince George together.

Iggy Pop has paid tribute to The Stooges' drummer Scott Asheton, who died on Saturday (15.03.14).
Scott - who retired from the band temporarily in 2011 after a stroke, but returned for their 2013 album 'Ready to Die' - died aged 64 due to an unspecified illness.
Scott formed The Stooges in 1967 with his older brother, guitarist Ron, who passed away in 2009, bassist Dave Alexander and Iggy, real name Jim Osterberg.
In a statement, Iggy said: "Scott was a great artist. I have never heard anyone play the drums with more meaning than Scott Asheton.
"He was like my brother. He and Ron have left a huge legacy to the world. The Ashetons have always been and continue to be a second family to me. My thoughts are with his sister Kathy, his wife Liz and his daughter Leanna, who was the light of his life."
The band's groundbreaking self-titled 1969 debut album was followed by 'Fun House' a year later and 1973's 'Raw Power', before the band split in 1974.
Scott went on to play in Sonic's Rendezvous Band, the Scott Morgan Band and Dark Carnival, before The Stooges reunited in 2003 and the line-up has included a number of contributing musicians over the years.
In 2010, Iggy and the Stooges entered the Rock And Roll Hall Of Fame and Scott was present at the induction ceremony.

Sir David Jason never expected to return to 'Only Fools and Horses' following the death of the show's creator.
The actor plays Del Boy in the popular British comedy - which has a special sketch for Sport Relief that will air on March 21 - and thought it was "the end" of the show when John Sullivan died in April 2011.
Speaking on 'The Michael McIntyre Chat Show', David explained: "As you know, unfortunately, bless him, John Sullivan, the creator of it all, very unfortunately died.
"And as Nick Lyndhurst used to say, Sullivan made the ammunition and we just fired it. So, he was the brains behind the whole thing. So when dear John died, we thought that was the end of it."
Retried footballer David Beckham came up with the idea of making a cameo appearance in the sketch, which also stars Nicholas Lyndhurst as Rodney Trotter.
The 74-year-old actor explained: "He said he had always loved 'Only Fools and Horses' and that it would be great to do something with me and Nick. So then the grapevine started to work as these things do."
David was captured by script and insists it all "came back" to him instantly and he didn't "even have to think about it".
He added: "Once I read the script that they intended to do, and I said yes I would do it, it was so much of Sullivan and so much of 'Only Fools and Horses' the original, that I said, 'Yes, let's do it'.
"When I got together with Nick for the first run-through it came back like that [clicks fingers]. I didn't even have to think about it.
"It's like anything, it's like falling off a log. As soon as I put on the gear and started to look at the script, back it came."

The 'I Can't Sing' musical has been forced to remove a joke about Andrew Lloyd Webber from its script.
The legendary theatre impresario went to see an early run-through of the West End show - which is based on ITV talent show 'The X Factor' - at the London Palladium in central London, which he owns, and executives decided to drop a line which mocks his recent production 'Stephen Ward' so as to not offend him.
A source told the Daily Mirror newspaper: "They didn't want to run the risk of upsetting him. After all, he does own the Palladium. Lloyd Webber is blissfully unaware."
Andrew's latest work - which is based on the Profumo scandal of the 1960s - opened in December last year but is now set to close on March 29 after poor ticket sales, which he anticipated.
Speaking before its opening, he said: "I'm resigned now to the fact that anything I do probably nobody is going to like."
'I Can't Sing' - which was written by comedian Harry Hill, with the financial backing of 'X Factor' mogul Simon Cowell - also pokes fun at a number of past and present employees of the show, including Dermot O'Leary, Cheryl Cole and Louis Walsh and will open on March 26.

Enrique Iglesias, OneRepublic and Jason Derulo will perform on 'The Voice'.
The BBC has drafted in big stars to perform on the singing competition's live shows this year, which kick off on Saturday (22.03.14).
The trio will join previously announced guest star Shakira, who is also a coach on the US version of 'The Voice' with Usher, Adam Levine and Blake Shelton.
'Talk Dirty' star Jason and 'Counting Stars' group OneRepublic will perform on Saturday's first live show.
Shakira and Enrique will perform the following week on March 29.
And BBC bosses are already lining up more big names for the grand final, which takes place in early April.
Jason said: "I'm thrilled and excited to be performing. 'The Voice' is an incredibly popular global brand and I thank them for inviting me to be a part of it. It's going to be a great show."
There will be just three weeks of live shows on 'The Voice' this year, with 12 acts competing to win the third series of the singing competition.
Viewers saw coaches Kylie Minogue, Sir Tom Jones, will.i.am and Ricky Wilson finalise their line-ups for the live shows on Saturday night (15.03.14).
Team Kylie will consist of Lee Glasson, Rachael O'Connor and Jamie Johnson. Tom's team includes Sally Barker, Georgia and Bizzi Dixon. Ricky has enlisted Chris Royal, Christina Marie and Emily Adams. Finally, will.i.am has taken Iesher Haughton, Sophie May and Jermain Jackson through to the live quarter finals.
One member from each group will be axed in Saturday's live show, with the eight remaining acts going through to the semi-final on March 29. Four acts will then compete in the final in April.

Louis Walsh won a bet with Simon Cowell to return to 'The X Factor'.
The 61-year-old music manager, who has been on the judging panel for the past 10 series, reportedly won a wager with Simon by agreeing to go on stage and dance with leprechauns at a recent showing of 'X Factor' musical, 'I Can't Sing'.
Simon, 54, challenged Louis to earn his place back on the panel by dancing in public with leprechauns, and Louis did just that at a preview of the theatre show in London last week.
A source told the Daily Star newspaper: "He certainly is game for a laugh. The audience gave him a standing ovation. Simon lost the wager and he clearly felt that anyone who is brave enough to do that deserves their seat back on the 'X Factor' judging panel."
'I Can't Sing' features caricatures of 'X Factor' judges Simon and Louis, who is depicted as a boy band-obsessed Irishman that dances with leprechauns.
Recent reports suggest Louis' place on 'The X Factor' is in doubt as returning judge Cheryl Cole wants him axed, but Simon is keen for his Irish pal to return.
Meanwhile, other candidates being lined up for a potential spot on the panel include LMFAO rapper Redfoo, former runner-up and 'Xtra Factor' presenter Olly Murs, and Black Eyed Peas frontwoman Fergie.

Holly Willoughby's son is over the moon about having a new baby brother or sister.
The 33-year-old star recently announced she is expecting her third child with husband Dan Baldwin and she says the best part about the experience has been breaking the news to son Harry, four, and two-year-old daughter Belle.
She said on Monday's (17.03.14) edition of 'This Morning': "It was lovely to tell the children, actually.
"When Belle came along, Harry was not even two yet, so he didn't really get it. This time he gets it and he came downstairs, and I was just waking up, and he went, 'I just wanted to come down and make sure you and the baby are OK.' It melts your heart! It's all lovely."
However, Holly - who also hosts 'Surprise, Surprise' and appears as a panellist on ITV2's 'Celebrity Juice' - admits it was difficult to keep her big news to herself for so long.
She added: "That first bit when you can't say anything is horrible because you just want to go, 'I'm pregnant!' But now it's nice that everybody knows and it's out there."
Holly and TV producer Dan announced their baby joy in a statement on the blonde beauty's official website last week.
She wrote: "Surprise Surprise (and it was a surprise!!) I'm really happy and excited to tell you that Dan and I are expecting baby number 3!!
"We feel blessed and very lucky to be giving Belle and Harry a little brother or sister later this year. (sic)"

Connor Cruise and mother Nicole Kidman have a "solid" relationship.
The 19-year-old DJ insisted rumours he is estranged from the Australian actress - who adopted him with then-husband Tom Cruise in 1995 - are wide of the mark and says his family mean "everything" too him.
He told Australia's Woman's Day magazine: "I love my mum. I don't care what people say. I know that me and mum are solid. I love her a lot. My family means everything. Yeah, I love my music, but the family comes before everything else."
It has previously been claimed that Connor and his sister Isabella, 21, have a strained relationship with their mother because of their ties to the Church of Scientology and Nicole - who has children Sunday, five, and Faith, three, with husband Keith Urban - even admitted they don't call her "mom" anymore.
Speaking in 2007, she said: "My kids don't call me mommy, they don't even call me mom. They call me Nicole, which I hate and tell them off for it."
She has also spoken of her sadness that the children opted to live with Tom after they separated in 2001.
She said: "They live with Tom, which was their choice. I'd love them to live with us, but what can you do?"

Amanda Seyfried thinks her kissing scene with Megan Fox was "really sexy".
The two actresses locked lips in 2009 movie 'Jennifer's Body' and the blonde beauty thinks she worked well with her co-star as they have "similar kissing styles".
She told W magazine: "We kissed really well together. We have similar kissing styles! If I watch the scene, it's actually really sexy."
However, the 28-year-old actress admits the scene in the film - about a cheerleader who killed and ate her classmates - was there "for the masses", but it still bombed at the box office.
She said: "We got it done for the masses, and, sadly, the masses didn't show up."
Despite a long line of movie credits, Amanda didn't feel famous until last year when her role of Cosette in 'Les Miserables' shot her to international stardom.
She said: "It may be that I'm older, and it may be that social media is everywhere now. I don't think I was really famous until last year - and I felt like no one paid much attention to what I was doing.
"That was good. But 'Les Mis' was an international hit, and that changed things. Before, I was a little more anonymous."

Lindsay Lohan wants nothing to do with her half-siblings.
The 'Mean Girls' star insists her father Michael Lohan's daughter Ashley - who was born in 1995 to Kristi Kaufmann, who he had a relationship with while separated from Lindsay's mother Dina - and son Landon, 13 months, who he has with girlfriend Kate Major, will never be welcomed into her family.
Lindsay - who has siblings Cody, Ali and Michael Jr. - said: "My dad has this whole other life with all these other people that he's created...and I do not want to be a part of that..
"They are not part of my life and they never will be."
Lindsay's comments came on her reality docuseries 'Lindsay' after she had a row with her father over dinner when she asked him to buy a car for 18-year-old Cody.
He protested: "I have child support...that's supposed to be for the kids."
Lindsay replied: "I do not want to talk about your two other random f***ing kids.
"Out of all of us Cody's the one that deserves something the most. It hurts me to see him not getting something that all his friends are getting...he doesn't have a dad to take him to soccer games...he needs his father."
However, Michael hit back: "Your mother cut me out of his life."
Later in the show, the pair also clashed again with the 27-year-old star furious at her father's criticisms of her friends.
She seethed: "They're people that you don't think were good for people. See, now you're getting me angry - because you weren't good for me for a long time in my life!"
Michael replied: "Well, if that's what you believe, that's fine, honey, I accept that though. I totally accept that."
Lindsay later added to the camera: "So my dad makes a nasty comment about my friends, it hurts me.
"They may go out and do what they want to do but they're not the kind of people who are going to do it around me, and that's what matters to me. They're good people.
"They've been there for me when I didn't have other people that were, you know, when other people weren't."

Charlie Sheen and Brooke Mueller threw a birthday party for their twins Bob and Max on Saturday (15.03.14).
The pair - who have been locked in a bitter custody war about their children - put their differences aside to plan the bash, which took place the day after the boys' 5th birthday.
Charlie's fiancée Brett Rossi - who also helped them work out plans for the celebrations - was also present at 'Anger Management' star's house for the party, gossip website TMZ reports.
The celebrations come after Brooke - who originally lost custody of the twins when she was placed on involuntary psychiatric hold at the UCLA Medical Center last year - moved back into the Mulholland Estates house the 48-year-old actor bought her.
The 36-year-old star is now taking care of her sons, rather than her brother, Scott, who was appointed their guardian before Christmas.
A source said: "Brooke has been living at the mansion in Mulholland Estates since before Christmas.
"The boys had been living at the house with their temporary guardian, Scott Mueller, but he hasn't been spotted at the house lately.
"He's been back at his house in Orange County [California] to be with his family. Brooke does have a nanny and a sober living companion also with her in the house. There just wasn't enough room at the condominium she had been living at for her staff."
Before Scott took custody of the boys, they had been looked after by another of Charlie's ex-wives, Denise Richards.
However, last November she relinquished care of the twins as she worried their violent behaviour was putting her daughters Sam, 10, Lola, eight, and Eloise, two, in danger.