"Thank you so much for all the great compliments about how I look on Bake Off!" she wrote.
"Truth is I'm having a very happy old age, am not averse to fake tan out of a bottle and all the glamour is added by Bambi and Debbie (the glam team) Sharon (wardrobe) and Jane and Claire the GBBO's stylists!
"Isn't it mad that at any age we ALWAYS think we look grim, should lose a stone etc.
"In 1969 (aged 29) I thought I'd die of shame if I hit ten stone.
"Now I look at that picture and wonder what I was on about: today I live in dread of hitting thirteen stone."
"But I'm very grateful for all the positive messages," she added. "Thank you so much."
The star added a "#bodyconfidence" hashtag.
Prue Leith on stage during the Music for Marsden concert at the O2 Arena, Greenwich, London. Picture date: Tuesday 3rd March 2020. Photo credit should read: David Jensen/ EMPICS Entertainment
File photo dated 14/2/2017 of Prue Leith who has said the way she brought up her children would not be acceptable today.
File photo dated 13/03/18 of The Great British Bake Off judge Prue Leith, who had admitted to a "slight feeling of panic" at turning 80.
Prue Leith attends the opening night of English National Ballet's Cinderella at the Royal Albert Hall in London. (Photo by James M Warren / SOPA Images/Sipa USA)
Prue Leith attending the Virgin Media BAFTA TV awards, held at the Royal Festival Hall in London.
Prue Leith attending the Mary Poppins Returns European Premiere held at the Royal Albert Hall, London
The Duchess of Cornwall (left) with Prue Leith at a reception to mark the 25th anniversary of the National Literacy Trust at Plaisterers' Hall in London.
Author Prue Leith with her husband John Playfair at a reception to mark the 25th anniversary of the National Literacy Trust at Plaisterers' Hall in London.
Michelle Hemsley (left) and Prue Leith with the award for Food Programme Sponsored by SMEG for 'The Great British Bake Off' during the 2018 TRIC Awards at the Grosvenor House Hotel, London.
Prue Leith with the Food Programme Award at the 2018 TRIC Awards at the Grosvenor House Hotel in London. Photo credit should read: Doug Peters/EMPICS Entertainment
The Duchess of Cornwall greets Prue Leith (right) at the Women of the Year Lunch at the InterContinental Hotel, in Mayfair, London.
Prue Leith attending the Specsavers' Spectacle Wearer of the Year Awards 2017 at 8 Northumberland Avenue, London.
The Duke of Edinburgh meets Prue Leith at the Duke of Edinburgh's Award gold award presentations, at Buckingham Palace, London.
Prue Leith who has been tipped to replace Mary Berry as a judge on The Great British Bake Off, attends A Very Special Afternoon Tea, with nutritionist to the stars Jane Clarke and dementia sufferer Terry Jones, to launch Nourish website & community, helping people living with cancer and dementia through the power of good food, real nourishment and expert support at the Royal Hospital Chelsea.
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Leith's post comes days after Bake Off viewers said they were stunned to discover she was 80.
The cook revealed her age during an episode of the Channel 4 show and viewers posted messages on Twitter telling of their shock, with many saying they had thought she was much younger.