Grilla #2
Creative Commons License photo credit: Tsar Kasim


The argument that weight loss must comply with the first law of thermodynamics seems at first glance to be rather unassailable. The first law of thermodynamics is the conservation of energy law that states energy can neither be created nor destroyed. From this the idea arose that a calorie is a calorie no matter what macronutrient (carbohydrate, fat or protein) it may come from.

Stated differently the commonly held belief based erroneously on the first law of thermodynamics is that:

Calories in = Calories out

Therefore, following this wisdom to lose weight one must restrict calories to less than what one requires each day or burn more calories through exercise than what one consumes each day. Unsurprisingly, this calorie restriction approach to weight loss does meet with some initial success. Of course most people just gain it all back and then some doing more harm to their health than good and around we go again. There must be more to this picture.

And there is. The problem with all this is that there is more than one law of thermodynamics. In fact it is the second law of thermodynamics that applies to living systems involving chemical reactions such as you and me. The second law of thermodynamics says that variation of efficiency of different metabolic pathways is to be expected. To quote Michael R. Eades M.D “if substance A converts to substance B via a chemical reaction in the body, then substance B has a lower energy than substance A. In other words energy is lost to the universe in that reaction. There is no reaction that doesn’t end up without a loss of some energy to the universe. This loss of energy is called entropy.”

In fact the thermic effect of nutrients is approximately 2 – 3% for fat, 6 – 8% for carbohydrates and 25 – 30% for protein (reference).

So applying the second law of thermodynamics we arrive at a much more complete picture:

Calories in = Calories out + Entropy

(Edit: Note how the left side of the equation still equals the right side)

Using protein and carbohydrates to demonstrate we see that:

100 calories from carbohydrates in = 94 calories out + 6 calories in entropy

100 calories from protein in = 75 calories out + 25 calories in entropy

That is a 19 calorie difference based on the same total calories consumed. So in consuming 100 calories of protein at least 25 calories will be lost due to the inefficiency of the chemical process leaving us with 75 calories with which to fuel our existence. Thus although two people one of which consumes 100 calories of carbohydrates and the other of which consumes 100 calories of protein both consume 100 calories the net effect is the person who consumed the protein ends up with less calories and so all other things being equal that person drops more fat.

This effect is compounded by the fact that protein is highly satiating and will never cause a blood sugar spike and subsequent crash the way poor management of carbohydrate consumption can. So the metabolic advantage of protein may amount to a couple hundred calories each day and over a sustained period of time this will equate to steady fat loss and body composition improvement. The last point is important because consuming ample protein is muscle sparing which means it helps you to not just drop weight which might include losing muscle and see you simply ending up smaller but still at the same body fat percentage but rather to drop fat and thus improve body composition.

If you would like to read more you can check out this study. As a final note I acknowledge that nutritionists when setting the kcal value for protein at 4 kcal per gram take into account the inefficiency of digestive protein. The actual kcal value of protein is closer to 5 kcal per gram. This acknowledgement of the inefficiency of protein under all conditions is different to the increase in inefficiency when protein has to be converted to glucose because the carbohydrate content of the diet isn’t high enough to meet the body’s glucose needs. This increased inefficiency is above and beyond that considered in the setting of the caloric content for protein.

Next, you might want to read about why (and how) not enough sleep and constant exposure to light is making you fat and sick.


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