The theory behind it is that there are 2 types of metabloism - A and B. People with type A deal with carbohydrates normally. When they diet they can lose weight easily by following decreased calories in minus increased calories out = weight loss. For people with metabolism B they respond to carbs differently and in a sense carbs actually make them put on weight even if their calorie expenditure is greater than their calorie intake. For all those people who find it almost impossible to lose weight no matter how careful they are with their meals and how much exercise they do it is likely they have metabolism B. It's a bit hard to explain but when I first read the book it was like it had been written about me!
It goes in 3 phases. 1st phase is elimination of carbs for a maximum of 8 weeks only. 2nd phase you start to reintroduce carbs but in a specific order. You do this phase for as long as is needed to reach your goal weight the final phase is the maintenance phase where you introduce even more carbs but by now your body can deal with them provided you don't go overboard with them because you have reset how your body works and responds to carbs in the 1st two phases.
If you google Dianne Kress you'll find lots of info about it. Hope this helps.