![Before and after weight loss photos of super slimmers](http://web.archive.org./web/20170207101306/http://i.dailymail.co.uk/i/pix/2017/02/07/02/article-4197574-3CE891D800000578-256_964x407.jpg)
Harriet Jenkins (pictured centre) from Southampton lost an incredible 15 st in 15 months - going from a size 30 to a size 10 - but seven years later she is back to square one. She is one of several 'Super Slimmers' to feature in a new Channel 4 documentary exploring why weight loss is so difficult to maintain. These super slimmers have won some of the dieting world's largest weight-loss competitions, but most of those featured have regained much of the weight. Around 40 per cent of people who achieve extreme weight loss - up to 20 st - put it all, or more, back on, experts say. And it's not just extreme slimmers: each year 30 million of us try to lose weight, and 10 per cent put it back on within three years. Leroy Wilson, 50, (left) who appeared on the front of a magazine three years ago after losing 20st in seven months put much of the weight back on after 'losing focus' and now weighs 23st. Jane Hall (right) from Lancaster was crowned Rosemary Conley's slimmer of the year in 2012 after losing 8 st over two years - but today she has put 5st back on.