Debunking The Dukan Diet

By Nicole German (RD, LD)

2266-the-dukan-diet.jpgThe Dukan Diet continues to be in the media spotlight with help from Kate Middleton, Jennifer Lopez and Giselle Bundchen who have recently endorsed the French plan.

This modified Atkins diet continues to take the world by storm especially after it’s recent “official” release in the USA. It is the number one diet right now in France, so what is The Dukan Diet really? Is it just another fad diet?

Dukan Fundamentals

Phase One: The beginning part of The Dukan Diet lasts one to ten days. During phase one, you may eat unlimited amounts of lean protein including soy, eggs, and lowfat dairy. You cannot eat anything else except 1.5 tablespoons of oat bran for some added fiber.

Phase Two: In the second phase dieters can begin to incorporate some of the 32 approved non-starchy vegetables. Depending on how long you are working on weight loss, this Dukan phase can last for months.

Phase Three: This stage of The Dukan Diet begins when you reach your goal weight. During phase three you can alternate phase two eating with some days of fruits, one cheese serving, and two servings of whole grain breads. Dieters still must eat nothing but protein on one day of the week.

Phase Four: This is the least restrictive phase of Dukan where dieters can eat whatever they like in moderation, but must follow phase one on one day each week to help maintain goal weight.


High protein diets long-term are never a good idea, especially for weight loss. Our brains need carbohydrates to function. Without those carbohydrates you may start to feel fatigued, light-headed, and moody. Some even report flu-like symptoms.

Low carb diets are designed to stimulate ketone production which happens when the liver converts fat or protein into fuel for your brain and body. This can be counterproductive if not enough protein is consumed because muscle loss could result. It’s important to consume the correct ratios of protein, fat, and carbs to ensure that fat is being converted to ketones and not the amino acids in proteins.

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Eating a high amount of protein also can put kidneys at risk by having to process the large amino acids, therefore, those with kidney issues should avoid Dukan. Constipation and diarrhea could potentially be other side effects because The Dukan Diet is very low in fiber in the first phase.

The Dukan Diet can come with risks, potential side effects, and wouldn’t be a suitable weight loss plan for everyone. It probably will turn out to be just another fad diet.


  1. roy

    wouldn’t a person on a fat loss diet, have a lot of fat on their body that could be used to make ketones, even a reasonably lean man (15% fat) would have 10’s of 1000’s of fat calories on their bodies.

  2. Gus

    Human brain DOES NOT need carbohydrates to function, it needs glucose. Glucose is easily & routinely produced from carbs but due to adaptive profile of our amazing human digestive system, we also can produce a secondary source of cellular fuel from protein sources. It’s called ketones or ketone bodies. Our brains are perfectly capable of shifting gears into using ketone bodies as primary source of energy. This is how nations survived through hunger crises through the history.

  3. Amy

    It worked really well for me when Weight Watchers, MFP, etc., were not effective anymore even after months of dieting and exercising. I was able to lose 14 lbs (initially wanted to lose 11) and also reversed my prediabetes, dramatically lowered my triglycerides back well into the normal range, increased my HDL, lowered my LDL … overall my annual physical after doing Dukan showed excellent results, including liver and kidney function (which are tested frequently due to a med I’m on). So for me, at least, it worked very well (and I did go through Consolidation as well; for Stabilization I just ate a balanced diet, no pure-protein days, and maintained no problem as long as I didn’t go crazy, i.e. around the holidays). I’ve had some times of yoyo-ing (in a 5-lb range) but my my metabolism has changed now that I’m in my upper 30s and I’ve figured out what triggers quick weight gain for me so maintaining should be much easier now going forward.

  4. Kellie

    I had success with Dukan, it might be the only diet I ever stuck to. I lost 30 pounds and gained back 14. Unfortunately NOW for the first time in my life, I get light-headed when I eat anything at all. My homeopath has me on Cataplex GTF and that worked but I tried going without it and its a problem. Not happy.

  5. Alice

    French people are actually having second thoughts starting the Dukan diet nowadays.. It is considered as one of the most damaging diets for one’s health and studies show that most dieters regain their weight + extra kilos once they go back to normal…

    • Gus

      All the diet modifications will result the same way if you go back to your un-regulated un-healthy habits. All the diets are restricting the body and shocking it. Therefore, due to survival & evolutionary construction of human body, it restores the lost fat storage sooner than before the diet started.

    • roy

      Of course you gain weight when you go back to normal, normal is how you out the weight on in the beginning. All diets give you the ability to get rid of unwanted fat, if you go back to normal, after any diet, you will put the weight back on, find a diet that you like that will let you lose the unwanted fat, then stick to that diet, for 80% of the rest of your life.

  6. Angie

    I’m a vegan and at my lowest weight ever! However, it’s only because I lost all my muscles and fat weighs less than muscle – I have a very high body fat and virtually no lean muscle mass. Vegans still need to excercise, but not excessively.

    • roy

      read any thing about healthy life and healthy aging, you will find, lean tissue is the way to go. Fat, fat, or skinny fat is the same unhealthy problem.

  7. JeffV

    Right on. Agree with you, Krobe.

  8. JeffV

    Well said, NEMO. I agree with you 100%. There is no way I could have better retaliated this ‘debunking’.

  9. Leslie

    I just don’t get all the diet and nutrition fads from ‘experts’ (government, and best-selling authors–doctor or not, etc.) If a person eats meat/poultry/fish, vegetables, fruit, nuts, olive oil, cheese, and yogurt – is that not a diet that provides all the complete amino acids a human needs? Why do we need bread, twinkies, muffins, candy, fruit juices and soft drinks, et al? The extraneous stuff people eat is not *real* food–it’s had to be processed extensively from farmer’s field to your kitchen counter to be made into an edible product. North America is a land of plenty and we’re sick from poor nutrition because the non-essential food we eat fills up the place in our diet for *real* food. Another diet book to help people lose weight … sigh.

  10. Nicole German (RD)

    Ok, here is what I trying to get at:

    Fats make ketone bodies, yes. No problem there. But, amino acids/protein will also be used to be converted into glucose and sometimes using muscle mass to do this.

    We could really get into this about the percentages of calories from protein, carbs, and fat. But, I won’t go into detail. All you have to do is look up major studies published (try the Seventh Day Adventist Studies), and you will find that the healthiest diets tend to be mostly vegetarian (including plenty of healthy carbs), and small amounts of lean meat and fish.

  11. SueK24

    I recently read a blog about the Dukan Diet on the Zone diet weight loss website. The blog, titled “A really dumb diet from France”, was written by Dr. Barry Sears, the creator of the Zone Diet. He backs up his statements with a list of references to published studies (you can find the references on website along with the blog). Here’s what Barry Sears wrote:

    “After experiencing so many years of ridicule (now effectively past history) with the Zone diet, I never thought I would possibly criticize another new diet unless it was either dangerous or just plain foolish. The newest diet from France is both.

    Called the Dukan diet, this program is a strange combination of the Atkins diet with a French twist. As usual, there are number of diet phases that have to be followed. The first one is downright dangerous as it recommends unlimited amounts of lean protein, 1½ tablespoons of oat bran and lots of water. The reason this phase is dangerous is because there are virtually no carbohydrates or fats to counterbalance the protein. My best estimate is in this first phase more than 90 percent of the total calories are coming from protein. This will overwhelm the liver’s capacity to metabolize the excess protein leading to a condition known as “rabbit starvation” (1). This was a condition experienced by early Arctic explorers who only subsisted on lean protein. They quickly became dehydrated as the body desperately tried to excrete excess ammonia (the first breakdown product of protein) through the urine that could not be converted to urea by the liver. This leads to dehydration, diarrhea, nausea, low blood pressure and fatigue. At least on the Atkins diet there was a lot of fat coupled with the protein to help the liver metabolize the ammonia from the protein into urea that could be easily removed in the urine.

    The dehydration from such a severely ketogenic diet explains the need for lots of water. As far as the oat bran, it contains virtually no carbohydrate, but lots of soluble fiber to help expand the stomach. Yes you will lose weight (primarily water) and insulin levels in the blood will drop dramatically, but you will reduce the elasticity of the blood vessels (2) and increase insulin resistance in the liver (3). The decrease in the elasticity of blood vessels increases the likelihood of a heart attack, (4) and the growing insulin resistance sets the stage for liver dysfunction that always promotes weight regain. This first phase is called the Attack Phase, I assume because it attacks your liver and your metabolism.

    Phase 2 of this diet is just as wacky. Now you increase the oat bran to 2 tablespoons per day and have some vegetables every other day. This phase remains a highly ketogenic diet, meaning the liver and blood vessels are still in a metabolic mess. This is called the Cruise Phase. I guess this means you are cruising for a hard landing even though you are still losing weight.

    If you last through the first two phases (about two months), you enter into the Consolidation Phase that is just as wacky as the Cruise Phase, but in the other direction. Now you can add non-starchy vegetables every day and a piece of fruit (I applaud these additions). But then why does this diet let the person start eating bread every day and rice and pasta twice a week plus two Porky Pig meals including dessert and wine (that’s the French twist). It’s like an insidious plot to demonstrate how quickly you will regain the lost weight, but now as newly synthesized fat. Of course, by following this Consolidation Phase, it is virtually guaranteed you will consolidate the lost weight into new stored fat.

    Finally, there is the Stabilization Phase where you can eat anything you want (mac and cheese, fried chicken, etc.) as long as you eat only lean protein one day each week. Fat chance you will ever get there.

    You probably won’t die on the Dukan diet, but you will mess up your liver metabolism making it much more difficult to lose the resulting regain of fat mass on the Consolidation Phase.

    I am frankly getting a cold sweat as I write this blog since I am sounding a lot like Dean Ornish yelling at Bob Atkins in the old days. But even Bob would say the Dukan diet is just plain stupid.”

    • roy

      …..and yet, Barry, in spite of all that you say is wrong with this diet, 10’s of 1000’s of people have lost fat weight this way, and many of them have kept it off. if you follow the diet, through, 10 days max on attack, (and you are advised to see your doctor first), then as many non starchy vegetables, as you like, every 2nd day, then, some fruits and a little more fat, when you are at your target weight, adding more starchy carbs and fat till you find your right balance for a lifetime of a stable healthy weight. What is wrong with that?

  12. Cade

    Hey these have been some solid comments. I have been a believer of a high protein-low carb diet, because I have seen it work well for me when I do it. I think there is a bigger factor and that is excluding fructose (or sucrose) but I know that it works. Also the whole high protein-low carb thing seems so relative to each person what that means. It seems to skew quite a bit from person to person. Either way I am going to get the book. Thanks Nicole for the write-up and thanks Nemo and others for the comments. Also for those that have read it…any tips from your personal experience doing it?

    • MP

      I did the Dukan diet for almost a year. I’m quite fit, in my mid twenties, and after YEARS of trying to lose those 10 extra pounds, I did it in less than a month with minimal effort on the Dukan diet. It was my first diet and like magic. Maintenance was okay, too. Protein once a week? Easy! The problem? I went on vacation and went crazy…moved back to the USA, and started eating all sorts of unhealthy food. Now going back to protein seems like too much for my insides (here the meats feel heavier than other countries, for some reason), so I am trying the other extreme, organic and vegan. I want to see how my body reacts, and then I will probably choose the middle ground but it is good to see what really works, and what makes you feel your best. I do hot yoga 5-6 times a week and hike 2-3 times, so we will see which diet works best for my activity level. Good luck in finding what works for you!

  13. Dan

    Seventh Day Adventists who are Vegetarian live longer than the Adventists who are not Vegetarian, as well as longer than the average American. Also, in the July 2009 issue of the American Dietetic Association entitled, Position of the American Dietetic Association:
    Vegetarian Diets it states,
    “It is the position of the American Dietetic
    Association that appropriately
    planned vegetarian diets, including
    total vegetarian or vegan diets, are
    healthful, nutritionally adequate, and
    may provide health benefits in the
    prevention and treatment of certain
    diseases.” In it, they cite evidence that Vegetarian diets lower the risk for cancer, heart disease, as well as obesity.

    Very few Americans are deficient in protein. However, refined sugar consumption IS way too high in America. I eat SOME sugar, but I try not to eat too much of it. I don’t know of any study that shows that whole carbohydrates with a lot of fiber are harmful, except possibly when they replace all good fats, such as monounsaturated fats. Most Americans do not consume that much fiber. I don’t really eat a low fat diet, since I eat a lot of nuts everyday. Nuts are associated with a decreased risk of heart disease. Eating carbs with soluble fiber like oats and barley have been correlated with lower rates of heart disease. A meat heavy diet can be improved by regularly eating nutrient rich organ meats, such as liver. Eating a lot of fish also improves a meat heavy diet. A Vegan diet can be improved by regular consumption of greens, as well as sea vegetables. Of course, both kinds of diets should be organic- it would be nice if there was fish was completely mercury free.

    • roy

      … Dan so do the latter day saints, who eat a varied diet, maybe it is there faith, you will find that the one thing common with all the long lived people in different parts of the world, is they have a deep spirituality, they have a community that believes in the same things as them, which is normally a good positive outlook and a caring for things around them and that leads to a happier disposition, eat real food, find a reason to be happy, and you will live longer (barring accidental death) than you will, living a negative life.

  14. NEMO

    For the record, I did not attack vegetarian diets; vegan dietary practices are not found in any culture in our history with long-term survival. A fact is not an attack.

    You bike 140 miles a week. I’d say you can pretty much eat whatever the heck you want with that activity level. Americans don’t move for the most part and you took my words, which are easily confirmed by looking at the data, and took them personally because you are an outlier, so you don’t fit the average statistic.

    I wish you well in health; there are healthy vegetarians, just as their are healthy meat heavy diet eaters. When you switch from looking at the outliers and look at across a group – Americans have a diet that is rich with protein, but poor for amino acid profile. They lack adequate and proper fatty acids and excessive levels of carbohydrate.

  15. Dan

    It seems pretty obvious that most Americans are consuming a very high percentage of protein from animal sources. Americans may be eating less beef than before, but certainly more chicken. Americans also eat quite a bit of cheese, which of course is a source of animal protein. You made some good defenses of your own diet, such as the good point that Amino Acids can be converted to glucose, but when you strayed to attacking the Vegan or Vegetarian diet, that only 1% of all Americans follow, then I think you are on shaky ground. I have eliminated a lot of meat in my diet, and I still have the energy to ride my bike 140 miles a week and up. I eat some high carb sources of protein, such as beans and rice, but also lower carb veg sources of protein, such as nuts and seeds. Green vegetables are also a low carb source of protein. Vegetarian sources of protein can be very complete, such as in soy, hemp, quinoa, and Amaranth- foods that most Americans do not consume. I eat plenty of carbs, including some refined ones, but I remain at the lowest weight I have been in thirty years. My triglycerides are only 55 and my blood sugar is normal, as well as my cholesterol. Carbs are not harmful as long as enough fiber is consumed and the person remains active as well. Your diet can be healthy, but the Vegan or Vegetarian diet can also be super healthy, as well as supplying plenty of high quality, digestible protein.

  16. NEMO

    I’d contend that Americans are eating protein from the wrong sources. If you look up data in ERS at the USDA, Americans consume more of their protein from wheat, corn and other grains, than they do from animal foods. It winds up being too much protein with way too many carbohydrates – the point of being excessive with carbohydrates.

    Don’t believe me – look up the FAO data for global consumption and you’ll see that other countries that are in better health eat a higher proportion of the protein and fat from animal sources than we do. Japan, Italy, Spain, France – each has better health statistics and each consumes a higher percentage of their protein from animal sources and a higher percentage of their fats from animal sources or olive oil – all except Japan consume more fat than we do, but Japan consumes way more fish, so they eat the most omega-3 fatty acids from diet.

    Thse countries also consume a hell of a lot less added sugars and refined foods.

    Quality protein is the key – one needs a specific level of amino acids, in the right ratio, daily and the only thing that provides that ratio is animal foods. Soy has it, but it also has inhibitors that block one amino acid from being fully bioavailble!

  17. Spectra

    Ha, this is exactly what I was thinking. Nemo, that’s a pretty good summary right there. I always get annoyed when people dis higher protein diets and say that too much protein will cause weight gain. I’ve only ever experienced weight LOSS when I eat a lot of protein and decrease my carbs. Besides, the average American diet is really high in protein–the reason so many people are fat is because they eat WAY too many refined carbs and grains.

  18. NEMO

    This has got to be the most pathetic attempt at debunking I’ve ever seen!

    High protein diets long-term are never a good idea, especially for weight loss.

    For the most part, unless there is a metabolic derangement, protein is self-limiting – it is next to impossible to eat a high protein diet when choosing ad libitum and not forcing the issue with protein powders and supplements. ADEQUATE protein is easily achieved ad libitum and something most Americans are not achieving with the proper amino acid ratio, so this approach works well to get your body attuned to how much protein — QUALITY PROTEIN — you actually need.

    Our brains need carbohydrates to function.

    The brain needs GLUCOSE. From dietary sources, glucose can be formed when carbohydrates or amino acids are converted to pyruvate in the Kreb’s Cycle. Glycogen can also serve as a source of glucose. And lastly the liver will utilize gluconeogenesis on an as needed basis whenever needed to prevent hypoglycemia.

    Low carb diets are designed to stimulate ketone production which happens when the liver converts fat or protein into fuel for your brain and body.

    Amino acids are primarily converted for glucose; fatty acids, from both dietary sources and stored fat, primarily for ketone bodies.

    This can be counterproductive if not enough protein is consumed because muscle loss could result.

    First you say it’s high protein, then you say this? Seriously? So is it high enough to cover muscle? Sure!

    ADEQUATE protein will not result in muscle loss and the data is clear that low-carb diets are muscle sparing when done correctly.

    It’s important to consume the correct ratios of protein, fat, and carbs to ensure that fat is being converted to ketones and not the amino acids in proteins.

    Amino acids aren’t primarily converted to ketone bodies. They’re converted mostly to glucose on an as needed basis and to replenish glycogen stores beginning at about week 2 because glycogen stores are depleted and homeostasis kicks in and restores them to normal levels, not stuffed to the gills levels like most Americans have!

    Eating a high amount of protein also can put kidneys at risk by having to process the large amino acids, therefore, those with kidney issues should avoid Dukan.

    Level 1 or Level 2 data please! Not speculation, not anecdotal – but hard data. Oh, that’s right there is none! Nice try – it sounds scary – bogga-bogga!

    Constipation and diarrhea could potentially be other side effects because The Dukan Diet is very low in fiber in the first phase.

    No, it’s problem is it is low in fat. Fat is better for colon health than fiber when you’re doing low-carb.

  19. Alexie

    Everyone would be better off eating the normal French diet: lots of salad, vegetables, fruit and beautifully prepared main meals that include plenty of protein and fat, accompanied by a nice glass of wine.

  20. krobe

    American’s are so naive. Read the book instead of “dejunking” the book. Dr. Dukan stated he had been doing this diet for 35 years and their hasn’t been one person, no one who has suffered from the results. Not even a person with one kidney. Yes, we need carbs but not the ones American people like to eat. If it has help 5 million French lose weight it is worth a try. They haven’t dropped dead from using it. A great book.

  21. Mike Howard

    Interesting carbsane!

    I think the low carb extremists who lionize the work of atkins see anything else categorized as “low carb” to be a knock-off. In some respects they are right. Insofar as the scientific rationale for what they define as too low in fat and too high in carbs? well, another topic for another day : )

  22. CarbSane

    What is hugely ironic is the chilly reception that Dukan has received on this side of the pond by the “legit” low carb community. It’s too low fat in the beginning two phases, too high carb/junk in the latter two phases. Can’t win 😉