Thermodynamics, for dummies

(versión en español: pinchar aquí)

First law of thermodynamics

It is the principle of conservation of energy. Applied to nutrition:

Energy Expenditure = What I eat + The Fat I Burn + The Muscle I Lose

The energy I spend comes from what I eat plus the fat/muscle I “lose”.


The grain diet (perfect for fattening the cattle)

Let’s say a man keeps his weight and body fat stable consuming 2000 calories / day:

Energy Expenditure = What I eat + The Fat I Burn + The Muscle I Lose

2000 = 2000 + 0 + 0

What happens if this person decides to follow the grain diet (i.e. living on bread, grains, pasta, pizza, etc.)? All these carbohydrates will skyrocket his blood glucose levels, and therefore also the insulin. Insulin gives a command to the adipocytes (fat cells) that they must store fat. Let’s suppose that from the total calories this person eats each day, 200 are stored as fat. Our organism has 200 Calories less available and therefore must adjust accordingly the energy expenditure and the food intake. The terms in red and blue must change to cope with this change:

???? = ???? + (-200) + 0

On the one hand the body forces the person to reduce his energy expenditure, for example making him more sedentary. A reduction from 2000 to 1900 Calories in energy expenditure. But he also needs to eat more to compensate for the Calories that are stored as fat instead of being used as fuel. That person goes from an energy intake of 2000 calories to 2100 calories.

1900 = 2100 + (-200) + 0

And day after day that person is storing a little bit more fat … not because he is sedentary and gluttonous, but because of an excess of carbohydrates in his diet. A sedentary lifestyle and an excessive appetite are consequences of being fat. And he becomes fat because of his bad food choices.

Trying to lose weight with calorie restriction (and failing)

Again, let’s say a person keeps stable his body fat consuming 2000 Calories/day:

Energy Expenditure = What I eat + The Fat I Burn + The Muscle I Lose

2000 = 2000 + 0 + 0

He burns 2000 Calories per day, which is the same amount he ingests. Now that person decides to lose weight by eating less: only 1500 Calories/day. The very first days of this new diet the energy expenditure is still 2000 calories, so his body is forced to burn fat and muscle:

2000 = 1500 + 300 + 200

As time goes by, his body reacts to the food restriction by cutting the energy expenditure. Now he spends 1500 Calories/day, the same amount he ingests and he stops burning fat:

1500 = 1500 + 0 + 0

But energy expenditure lows further to 1400 calories, and he begins to accumulate as fat those calories that are not used:

1400 = 1500 + (-100) + 0

There has been fat burning, but only temporarily. Soon he regains the lost weight. He ends up with more fat and less muscle than before. And always hungry.

Lose weight with carbohydrate restriction

As we did before, we start with a person who doesn’t burn fat:

Energy Expenditure = What I eat + The Fat I Burn + The Muscle I Lose

2000 = 2000 + 0 + 0

We restrict carbohydrates, which makes blood insulin levels fall and our body begins to burn fat. Suppose that now our body has suddenly 500 extra Calories, those coming from the body fat, and our body has to find a way of getting rid of them!

???? = ???? + 500 + 0

Our body has to change the terms in red and blue to accommodate those 500 calories:

  • a) it increases our energy expenditure, it “gives usmore energy”, urging us to move more, and increases the body temperature, and
  • b) reduces hunger with the aim of lowering the caloric intake, since it already has some calories from fat and there is no need to eat as much as before:

2250 = 1750 + 500 + 0

Thus, the person ends up burning fat (500 calories), with more energy (2250 Calories) and eating more than people on other diets (1750 calories intake compared to 1500 of those trying to lose weight by “eating less”, plus 500 Calories from fat). The 1750 Calorie intake may seem like a “calorie reduction” because this guy started with 2000, but it is not, since there are 500 Calories more from fat. In total the organism receives 2250 calories, so there is no “caloric restriction”. Our body does not feel under attack, it does not miss food (rather the opposite) and it will not react by reducing the metabolism. This situation is sustainable in the long term, which can allow us to lose weight significantly.

Thoughts on the irrelevance of appetite and calories

Some people believe that diets low in carbohydrates are useful to lose weight because fats/proteins have the effect of reducing the appetite and therefore the caloric intake. Decreased appetite causes reduced intake, reduced intake causes weight loss. It is an erroneous reasoning, based on the erroneous theory “Calories In Calories Out” (see). The reality is that, as we have seen, eating less with low-carb diets is a consequence of burning fat, not its cause.

The official dogma tells us many ways to control our appetite, as if it was true that not eating or eating less would lead to losing weight. Focusing on appetite control is focusing on caloric restriction, and that does NOT work to lose weight. To lose weight you have to focus on what you eat, not on how much you eat. If you count calories, you end up choosing foods that make you obese (see): counting calories is not just useless, it’s worse than that, it is counterproductive.

Eat so you activate fat burning. When you burn fat your body has “extra calories” to get rid of. How is it going to do that? It’s not your problem, nor should you worry about that. Do you need to count how many times you breathe per day to do it right?

Maybe all this seems like science fiction. It seems to me that fits well with scientifically proven facts, e.g. that caloric restriction diets do not work (see), and diets low in carbohydrates make people lose more weight than other diets, even when eating the same amount of calories (see), they do not reduce energy expenditure as much as other diets (see) and they naturally reduce the appetite (see).

Low-carbers say they feel more energetic throughout the day ( see ), and with a constant supply of energy, without ups and downs, and they also say that on this diet they notice their body warmer (seesee) . And I’m not talking about the different thermic effect of the food we eat, but of the effect caused by burning fat.

I recommend the graphic explanations of Lindha about the laws of thermodynamics.


2 thoughts on “Thermodynamics, for dummies

  1. Vicente, what an excellent mathematical treatise to explain how low carb works. Being mathematically inclined (i’m an auditor and use a lot of statistical sampling in my work, which is literally a numbers factoty) this made everything perfectly clear to me.

    I admire your ability to present complex issues in a simple form, always supported by credible studies.

    I have a question for you: I always read conflicting opinions on hard cheese in a low carb diet. Some say, eat all you want, some say limit it to 4 ounces daily and some say avoid it because although it is low in carbs and high in fat, it raises insulin. The same arguments are made for whey protein powder. What is your opinion?


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    • Hi Tony,
      for sure this is not the proof that low-carb works, but it explains that the “metabolic advantage” is possible and in no case that idea goes against the “universe laws”.

      AFAIK dairy creates an insulin response bigger than that predicted by its carb count. I am not sure that is something bad if you are healthy and in the context of a healthy diet. I eat cheese in moderate amounts and I also drink kefir on a daily basis. I believe there is no hard rule for this, but N=1 experimentation.

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