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Protein Mythology... get the Facts!

[Part-2: The Dukan Diet]

One common tactic in fad-diet books is to attach various notions (false claims, baseless theories, etc.) to a valid piece of scientific information.

A consistent thread of this sort you will find among high-protein/low-carb diet books has to do with the fact that protein takes more calories to process than other calorie-containing macronutrients (carbohydrates, fat, and alcohol).

Dr. Dukan writes on page 19 of his best seller (The Dukan Diet), “the specific dynamic action of proteins is 30% while it is only 12% for fats and just 7% for carbohydrates.”

On page 21 of The 17-Day Diet, Dr. Moreno writes that “Digesting protein takes more energy (calories) than digesting carbs or fat does…”

The argument that these fad-diet authors attempt to put forth is that there is a metabolic-caloric advantage secondary to high-protein intakes. Not really.

As I have noted in earlier blogs (...Protein for Healthy Weight Loss), adequate protein intake is not just important but critical in order to maintain both your bone mineral density and lean body mass while following a reduced-calorie intake. Additionally, protein offers the very real advantage of keeping hunger at bay longer between meals.

You won’t however find a bullet point in my list of protein’s attributes that mentions that processing it burns more calories, despite the fact that processing protein does burn more calories than metabolizing “carbs,” fat, or alcohol. So, why the omission?

Before I go into the details of explaining why, we need to pause for a definition.

Thermic Effect of Food (TEF) refers to the energy (calories) required to metabolize energy-containing nutrients (protein, carbohydrates, fat, and alcohol). An older out-dated term for TEF is “Specific Dynamic Action” (SDA). Your daily total energy expenditure consists of TEF, resting metabolic rate and physical activity.

Protein does have the highest TEF with the cost of a) protein synthesis, b) gluconeogenesis (conversion of certain proteins to glucose), and c) urogenesis (making urea out of protein byproducts) amounting to 25% of the protein calories ingested. Meanwhile the cost turning carbohydrates into glycogen (and storing in your muscles or liver) costs only 7.5% of “carb” calories, and finally, storing ingested fats costs just 2.5% of fat calories.[1], [2], [3]

Please note that the numbers for TEF that I have just stated are averages identified by experts in this topic. While there is a wide variability in the TEF of different sources of both protein and carbohydrate, Dr. Dukan’s numbers, in the earlier quote, are not correct averages. In fact, his number for the TEF of fat simply appears to be a typo.

At first glance it would seem that the cost of metabolizing protein--on a high-protein diet--should provide a significant advantage. The fact is however that the magnitude of increased TEF on low energy diets doesn’t amount to anything of practical significance. Take a look:

The above chart compares the TEF of a high-protein, high-carbohydrate (CHO), and "balanced" 1,400-calorie diet. The TEF of the high-protein distribution is just 38-calories higher (per day) than the high-carbohydrate diet, and just 33-calories (per day) higher than the balanced diet. It would take around a 100-days to lose one additional pound based on that difference. Not only that, but if you have any experience dieting you know the chances of sticking to a highly-restrictive-regime for 100-days is also pretty slim. This is why the higher TEF of protein is essentially a mute point, not of practical significance, as Golay notes based on his data on this topic, "The relevance of TEF on low-energy diets must be questioned."[4]

That said, the above high-protein distribution looks more like South Beach, or The Zone, than Dukan. Nonetheless, go ahead and crunch the numbers. Even using the Dukan Attack and Cruise Phases you still won't be impressed at what little there is to be gained for your (extraordinary) efforts.


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*Calculation based on above stated average TEF values: 25% for protein, 7.5% for carbohydrates, and 2.5% for fat.[2]

[1] Stubbs RJ, et al. Annals of the New York Academy of Sciences 1997;819:44-69.
[2] Hall KD. Am J Physiol Endocrinol Metab. 2010;298:E449-E466.
[3] Kinabol JL, et al. Br J Nutr 1990;64:37-44.
[4] Golay A. Am J Clin Nutr 1996;63:174-178.

Reader Comments (2)

Excellent post and review!

July 31, 2011 | Unregistered CommenterSylvia White RD

Thank you, Sylvia!

August 1, 2011 | Registered CommenterDorene Robinson RDN CDN

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