Overview of the Low-Carb and Low-Fat Dukan Diet

What Makes the Dukan Diet Different

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The Dukan Diet is named after French physician Pierre Dukan, who created the plan. The weight-loss phase is very low in fat and carbohydrates. The dieter alternates between periods of eating "pure protein" and eating "protein plus vegetables" until reaching his or her "true weight." After the weight-loss phase, dieters advance to a long consolidation phase where some fruits and starchy foods are added, before culminating in a maintenance phase.

Problems With a Diet Low in Fats and Carbs

Although the Dukan Diet is usually billed as being a low-carb diet (and it is) the emphasis is even more on keeping fats in the diet very low. Fats are considered "the absolute enemy", worse than carbohydrates, and "representing every danger possible." In fact, one of Dr. Dukan's big issues with most low-carb diets is that "mistrust of fats is gone, and once gone makes any form of stabilization impossible." (Apparently, he isn't aware that for many of us, healthy fats are what make weight stabilization possible. For some, they even stabilize mood.) There are some inherent problems with attempting a diet that is low in both fats and carbohydrates, especially one that is structured the way the Dukan Diet is.

Big Protein Difference: Diet Recommendations vs. Dukan Diet Restrictions

The National Academy of Sciences, which carefully reviews the research, currently recommends that between 10% and 35% of calories come from protein. And the recommendations of most low-carb diet authors are within these parameters. The Dukan Diet, on the other hand, is in the neighborhood of 79% to 90% protein, depending on the specific food choices. This is not a good idea. The main concern with eating too much protein is that our livers and kidneys have to work to process the byproducts of protein metabolism, and there is a limit to how much protein they can deal with. Dr. Dukan says that drinking a lot of water will take care of this problem, but he doesn't provide any references to back this up.

People often don't feel very good eating an all-protein diet. The phenomenon known as "protein poisoning" or "rabbit starvation" (because rabbit meat is very lean, and people having to exist on it experienced starvation) shows itself in gastrointestinal disturbances, headache, low blood pressure and malaise. This could be why people don't feel like eating a lot on a protein-only diet -- it makes you feel sick after awhile. Additionally, if you are getting way more protein than you need, your body will convert a fair amount of it into glucose (gluconeogenesis). Although it's nice that this glucose is produced slowly compared to eating sugar (people on low-carb diets benefit from this), in excess it can counter some of the positive effects of following a low-carb way of eating. Also, too much protein will give you bad breath, in the form of ammonia. This is different than keto-breath, though the two can occur together.

The Importance of Fat Long-Term

Even so, early in a low-carb weight loss plan, it is probably less dangerous to eat a lower-fat diet, simply because the dieter is metabolizing a lot of body fat (although it still could be unpleasant and may not be sustainable for too long). As time goes on, however, weight loss slows and it becomes more important to add fat to the diet. Other than the issues of eating a protein-only diet, I find other problems with the Dukan plan, as well as some things I think are positives.

Positives of the Dukan Diet

I like the concept of a long consolidation phase. Many low-carb diet approaches have fairly short pre-maintenance or transition phases; this may be a mistake. There is undoubtedly a tendency for the body to resist maintaining fat loss, especially if that loss was substantial. Having a fairly long period of time where people are extra aware of this and taking steps to combat it is probably a good thing.

I also like the emphasis on a realistic expectation of a sustainable weight loss, which Dr. Dukan tries to achieve with his concept of the so-called true weight (similar to my lowest sustainable weight concept). While there are quite a few exceptions, I have seen quite large numbers of frustrated dieters who give up because they aren't able to achieve or maintain the goal weight they originally set. From my reading of the research, plus observations of several decades, I would guess that the vast majority of people will not sustain a weight loss of more than 20% of their body weight over time, and for many (and possibly most) it's more in the range of 5% to 10%. Happily, most of the health benefits of weight loss do occur in that range of weight loss. Our bodies were simply not designed to embrace large amounts of weight loss (which makes sense when you think about it).

More Negatives of the Dukan Diet

Adequate Nutrition: With about half of the days in the weight-loss phase being pure protein, with no vegetables allowed, there is a real concern with getting adequate nutrients on the Dukan Diet. Certainly, on the pure protein days, there are many vitamins that will be lacking. These may or may not be made up on the other days. Dr. Dukan takes a laissez-faire attitude about vitamin supplements (it's okay if you do or if you don't). Phytonutrients are going to be lacking as well. Also, if a person chooses very lean proteins, fat-soluble vitamins and some of the phytonutrients may not be absorbed well.

The diet is very calorie-phobic, especially for a diet that doesn't restrict the amount of food. It's odd to keep going on about calories when you aren't restricting portions; it could be confusing to people trying to follow the diet.

Salt is Minimized: This is a concern on a low-carb diet for a couple of reasons. First of all, it's usually an unnecessary reduction in the palatability of meals, which means it could be another nail in the coffin of your willingness to stick with the diet. In the standard American diet, the vast majority of sodium comes from processed foods. Low-carb diets are low in such foods, and so is the Dukan Diet. (Also, for most of us, salt is just not that big a deal.) Worse, especially in the first weeks of a low-carb diet, some of us actually need to eat more salt when eating a diet low in carbs, as sodium is lost.

Dairy vs. Vegetables: Fat-free milk and yogurt are on the unlimited list (and in some of the menus there are as much as 2 1/2 cups of yogurt per day). Dr. Dukan brushes aside the milk sugars in these products, saying the number of sugars is too small to worry about. But then he restricts low-starch vegetables, which are even lower in sugars/carbs. Drink all the milk you want, but forbid spinach? This makes no sense at all to me.

Factual Errors

There are many statements of "fact" in the book that are either false or highly questionable. Here are just a few:

  • Dr. Dukan puts the carbohydrates in root vegetables and whole grains in a category he calls "slow sugars," meaning that they supposedly break down into sugar slowly in our bodies compared to refined grains and sugars. This is very misleading. Many starchy vegetables raise blood sugar even faster than refined sugars, and the carbohydrates in any grain that is ground into flour, whether whole or not, raises blood sugar quickly.
  • Dr. Dukan states that the Atkins Diet causes "cholesterol and triglyceride levels to rise dangerously." In the case of triglycerides, the opposite has been widely documented. In the case of cholesterol, the situation is more complex, but certainly, HDL ("good") cholesterol usually rises, and the LDL cholesterol pattern changes to the less dangerous pattern A (in a person who has the more dangerous B pattern). This, again, is very well-documented.
  • Dr. Dukan writes that when needed we "transform our fat reserves into glucose." This is simply erroneous. One of the main reasons that low-carb diets work the way they do is that fats are used directly for energy. They do not raise blood sugar because they can't be turned into glucose.
  • He claims that there is a "golden proportion" of macronutrients that are easily assimilated by our bodies and that deviating from this proportion means that calories are not absorbed as well and weight loss is promoted. That proportion is 5: 3: 2 of carb: fat: protein. As far as I know, this is unfounded. (Dr. Dukan says it's true because human milk is in this proportion, but that means nothing to an adult.)
  • He says, "When they are combined, water and pure proteins act powerfully on cellulite." Again, 100% unfounded as far as I know.
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  • In summary, I think that not many people would stay the course for the whole Dukan Diet regimen, and if they did, I would be concerned about their health. This is a fat-phobic/low-carb diet that I do not recommend for any extended amount of time.
    Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005), Food and Nutrition Board, National Academy of Sciences.
    Leroux, MarcusFoster-Powell, Kaye, Holt, Susanna and Brand-Miller, Janette. "International table of glycemic index and glycemic load values: 2002." American Journal of Clinical Nutrition. Vol. 76, No. 1, 5-56, (2002).