I hope nobody minds if I share my experience with the Dukan Diet. I don't want piss on the Dukan parade, but it should come with a warning.
Positives: if you follow it to the letter it definitely works as advertised.
Negatives: it can really screw your adrenal glands make you feel like crap.
I started it in April. Wanted to lose 5 - 8 lbs in a hurry, and absolutely followed the Attack Phase to the letter. Didn't feel hungry, really noticed weight loss in a hurry, but on day 5 of the attack phase, I started waking up at night at 1 am and was wide awake past 4 am, feeling my heart pounding and the blood racing around my body like I'd had four pots of coffee before going to bed. Same thing the next night and the next night and the night after.
Asked a physician friend of mine what might be happening (in the guise of "this is happening to my friend" :o and he said that an all (or mostly) protein diet lowers blood sugar so far down in the night that the body goes into a ketotic state and the adrenals start pumping out cortisol which has the effect of releasing glucagon where it's stored in the muscle and converting it to blood glucose to raise blood sugar. A massive adrenal discharge of cortisol will wake you from sleep and make you feel completely frantic and wired.
I immediately started adding complex carbohydrates (mostly vegetables and some low-glycemic-index fruit) to my diet. Minimal change. Awake from 1-4 am and dead tired the next day. Added more fruit and whole grains. Minimally better, again. Gave up the Dukan Diet but tried to eat healthy and increase excercise. Didn't help the night waking and general feeling like crap.
It took months to lower my daytime cortisol and start sleeping at night again, and I felt like utter dragged-through-the-road crap for all those months.
For me, the Dukan diet wasn't worth how much it stressed my adrenals.
Now, a couple of things may have worked against me - it would be unfair of me to blame it all on the Dukan Diet because I think I may have been stupid when I started it.
I may have been predisposed to adrenal problems with an all-protein diet because I was pretty stressed anyway. Also, I was not overweight when I started, I was average weight but wanted to return to my very slim days - I just wanted to lose those 5-8 lbs that had crept on since I completely gave up breastfeeding. And finally, I may have stretched the Attack Phase out too long. In the book it says (if I recall correctly) that you can do the Attack phase for up to ten days (I think, please correct me if I misremember). So that's what I thought I'd do, even though that wasn't what the book recommended for the little weight I wanted to lose.
I still think the Dukan Diet can work, and work extremely well, but I think it needs to be followed to the letter, especially in the Attack Phase, and I think if anyone starts to experience night wakening and feeling horribly distressed and wired, they should come off the diet completely at once.
I really hope this helps - I'm not trying to be miserable about the diet, I just really hope sharing this helps someone else avoid what happened to me.