She's a fashion icon and now a princess. So how did Kate Middleton manage to squeeze into that size 2 wedding dress? Was it pre-nuptial nerves or were the rumors true that Kate and her mother Carole turned to the controversial Dukan Diet, developed by French Doctor Pierre Dukan. It's all the rage in Europe and was just introduced to the U.S. in late April.

Clinical Nutritionist Brian Higginson from Swedish Medical Center says the diet may be new, but the concept isn't.

It's a diet that is very similar to the Atkins Diet where it is very, very high in the protein content, but then it does vary a little bit because it does focus on leaner protein foods, said Higginson.

That means skinless chicken breasts, fish and lean cuts of meat.

The diet is divided into four phases:

First up -- the Attack Phase. You eat only lean protein, add in a little oat bran and do 20 minutes of exercise a day. A walk is fine. This part lasts 2-7 days depending on how much weight you have to lose.

Sports Nutritionist Susan Kleiner says that jump-start can be a good thing.

The concept of giving you this kind of initiation phase where it's very black and white..for a lot of people that's helpful, said Kleiner. Too many choices can be difficult.

Holistic Nutritionist Beverly Kindblade agrees.

Being mostly high protein not having very many other foods, you're probably going to lose a lot of water weight and start feeling great, said Kindblade.

Next is phase two -- the Cruise Phase. You alternate protein only days with with protein and non-starchy vegetable days. Continue on this path until you reach your personal weight goal.

Phase three -- the Consolidation Phase. Add in bread and some fruits. Have a celebration meal once a week. Stay here five days for every pound lost. A 20-pound drop means 100 days.

Think you're finished? Not quite. Whether you're a princess of a pauper you never completely go off the diet.

Next starts the Stabilization Phase for lifetime maintenance. Eat what you like, but have a protein-only day once a week.

Follow these simple rules and the Dukan diet promises quick weight loss -- as much as seven pounds in the first week -- and long-term results without being hungry or counting calories. Sounds like the perfect weight loss plan, doesn't it? However there are some downsides.

Beverly Kindblade says the diet is likely to affect your mood.

The grain-fed meats are really high in Omega 6 fats which promote inflammation, so I think people are going to feel a little inflamed, a little achy, maybe not be sleeping so well in the long term on that diet, she said.

Susan Kleiner wonders how dieters will be able to keep up their energy levels.

I love that they say you should exercise. I'd like to see someone really exercise on this diet. There's not enough carbohydrate in these first couple of weeks, even in the first five days to fuel any exercise. In fact they say the side effect of the diet is fatigue, said Kleiner.

Brian Higginson points out that the diet can be downright dangerous for some.

The Dukan Diet might be problematic for people with any sort of kidney disease or decreased kidney function. because the high intake of protein, he said.

Those concerns aside, will the Dukan Diet work long term? Our panelists weigh in:

  • Beverly says that depends on your motivation and discipline
  • Brian believes you can lose weight, both in the short-term and in the long-term
  • Susan is skeptical that dieters will be able adhere to the diet indefinitely

So overall, how do our three panelist rate this diet? We asked them to give us a thumbs up or a thumbs down.

The verdict: a unanimous thumbs down for the Dukan Diet.

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