The former Ladette to Lady star, who runs her own cookery school in Tunbridge Wells, admits: 'I have been on every single diet you can imagine in life.
'To me, when you say diet you say failure. So it's all about mindset. I have been big forever and I have never found something that I can sustain.'
However, Rosemary has now finally found a balanced diet that works for her, featuring one very special secret ingredient - prunes.
'I love prunes - this is not a wind up! I seriously love them, and I have always loved them, and I eat them like sweets,' she says.
'I've lost two dress sizes and I feel a lot better in myself – my skin is clearer, my arthritis has eased, everything is better.'
Rosemary, pictured in January 2016 on the left and December 2016 on the right, says she doesn't weigh herself, but has lost 14cm and hopes to slim to a size 18
The diet Rosemary has been following is based around the California Prunes Eating Plan, which was created by dietitian Jennette Higgs after research from the University of Liverpool showed that 'eating prunes as part of healthy lifestyle eating can aid weight loss by inducing increased feelings of fullness'.
'I have found that my tastes have changed,' Rosemary explains. 'Prunes give you that sweetness if you need a little bit of a hit - I don't have my fizzy drinks at all anymore!
'I had some bread the other day and I was in agony. Your body becomes attuned and that's when your mindset changes and you automatically start to lose weight.'
She adds that she hopes to start exercising soon, saying: 'I've got a plan in action - but I am naturally lazy so it's going to be tough. What I've got to do is find something I enjoy.
'I used to be quite frightened to walk to the shops, because I was worried I wasn't going to get back. That's how bad I was. But I walk everywhere now.'