Dukan is a low carb diet...and supposedly one of the more restrictive ones.
I have been doing a version of LCHF.....low carb,high fat. In 3 months I lost 1 1/2 stone,and was never hungry.
This type of diet is not faddy-it's been around for quite a few years,and is gaining more and more support as it is ideal in some cases for diabetics. It has been adopted by health officials in Sweden to help tackle that country's obesity problem. Apparently low carb works because carbs cause the release of insulin-which in turn causes the body to hold on to fat.
It's based on natural food....no processed rubbish or low fat ready meals.
There is some good information here -
http://eatlikeaswede....rb-high-fat-approach/
And here -
http://www.dietdoctor.com/lchf
It's worth checking out...but of course a diet has to work for YOU and your lifestyle.