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one single food group, the only possibility is lean proteins—a satisfactory solution as far as taste is concerned. It also avoids the risk of clogging up the arteries, and by definition it excludes protein deficiency.
    When you manage to introduce a diet limited to protein foods, the body cannot use all the calories contained in the food. The body takes the proteins needed for survival and for the vital maintenance of its organs (muscles, blood cells, skin, hair, nails), and it makes poor and scant use of the other calories provided.
    Assimilating Proteins Burns Up a Lot of Calories To understand the second property of proteins that makes the Dukan Diet so effective, you need to familiarize yourself with the idea of the specific dynamic action (SDA) of foods. The SDA of a food represents the effort or energy that the body has to use to break down the food until it is reduced to its basic unit, which is the only form in which it can enter the bloodstream. How much work this involves depends on the food’s consistency and its molecular structure.
    When you eat 100 calories of white sugar, the work the body must doto absorb it burns up only 7 calories, so 93 usable calories remain. Thus the SDA for carbohydrates is 7 percent.
    When you eat 100 calories of butter or oil, assimilating them is a bit more laborious. The body burns 12 calories in absorbing them, leaving only 88 usable calories. Thus the SDA of fats is 12 percent.
    Finally, to assimilate 100 calories of pure protein—egg whites, lean fish, or nonfat cottage cheese—the task is enormous. This is because protein is composed of an aggregate of very long chains of molecules whose basic links, amino acids, are connected to each other by a strong bond that requires a lot more work to be broken down. It takes 30 calories just to assimilate the proteins, leaving only 70 usable calories. Thus the SDA of proteins is 30 percent.
    Assimilating proteins makes the body work hard and is responsible for producing heat and raising our body temperature, which is why swimming in cold water after eating a protein-rich meal is inadvisable, for the change in internal body temperature can result in immersion hypothermia.
    This characteristic of proteins, annoying for anyone desperate for a swim, is a blessing for overweight people who are usually so good at absorbing calories. It means they can save calories painlessly and eat more comfortably without any immediate penalty.
    At the end of the day, after eating 1,500 calories worth of proteins, a substantial intake, only 1,050 calories remain after digestion. This is one of the Dukan Diet’s keys and one of the reasons why it is so effective. But that’s not all.
    Pure Proteins Reduce Your Appetite Eating sweet foods or fats does create a superficial feeling of satiety, all too soon swept away by the return of hunger. Recent studies have proved that snacking on sweet or fatty foods does not delay your urge to eat again or reduce the quantities eaten at the next meal. On the other hand, snacking on proteins does delay your urge for your next meal and does reduce the amount that you then eat. What is more, eating only protein foods produces ketones, powerful natural appetite suppressants that are responsible for a lasting feeling ofsatiety. After 2 or 3 days on a pure protein diet, hunger disappears completely, and you can follow the Dukan Diet without the natural threat that weighs down most other diets: hunger.
    Pure Proteins Fight Edema and Water Retention Certain diets or foods are known as being “hydrophilic”—that is, they encourage water retention and the bloating this causes. This is the case for mostly vegetable diets, rich in fruits, vegetables, and mineral salts. Protein-rich diets are the exact opposite. They are known to promote elimination through urine and, as such, provide a welcome purge or “drying out” for tissues gorged with water, which is a particular problem during the premenstrual cycle or during