It is probably safe to say that the most commonly held belief in nutrition today is that “a calorie is just a calorie”. In Nutrino, we always like to remind people to take this sentence with a grain of salt. The goal of this post is to explain why in Nutrino we don’t like to emphasize calorie counting.
So what are calories?
Calories are nothing but a unit of energy. Calories were invented in 1824 by the French physicist Nicolas Clément. More precisely, a calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree celsius (at sea level). In nutrition, we typically use kilocalories (although people often refer to them as ‘calories’ as well, which is a misnomer). 1 kilocalorie is equal to the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree celsius (in fact, Clément used the word calorie because in Latin calor means heat).
Then what do calories have to do with nutrition?
In the early 1900’s a German doctor named Carl von Noorden tried to use concepts from physics to study obesity. Van Noorden hypothesized that “a calorie is just a calorie” and claimed that no matter what you eat, if you consume more calories than you burn you are going to gain weight. In his view, there is just no way around it. This he said, is the result of the first law of thermodynamics, stating that
energy must always be conserved.
The energy you get from food cannot vanish. According to von Noorden, you either use it or store it as fat. We will later see that it can be used in other ways as well.
How do we know how many calories food has?
The original method was to place the food in a sealed container surrounded by water. Then the food was completely burned to ashes and the resulting rise in water temperature was measured. The number of calories in the food is defined to be the energy required to burn the food (and was measured by the change in temperature). This method is no longer used. Today we know that every gram of carbs or protein requires about four calories to burn, and every gram of fat requires about 9 calories to burn. This allows one to estimate the amount of calories in food just by knowing its composition of macronutrients.
Although “calorie in-calorie out” is a commonly held belief in nutrition and people are often obsessed with calorie counting, there are in fact a lot of problems with it.
Now I’m not going to argue that the first law of thermodynamics is false (the author is a trained physicist…) But what I am going to argue is that the notion of calories is misinterpreted in nutrition.
There are two issues with the caloric theory of food:
First, the driving mechanism behind caloric intake in the body is absorption, and not combustion. Our body is not a giant engine that burns the calories, it tries to absorb the calories to use them. This means that in the process of absorbing food, the body uses energy. Since the body is a complex biological system, it absorbs different calories in different ways. The absorption depends on the composition of the food. This means that a person who is eating a 2,000-calorie diet only from fat should burn a different amount of energy than if he would be eating a 2,000-calorie diet from carbs (by the way, this has to do with the second law of thermodynamics ).
This means that not all calories are created equal. In a 2012 study researchers followed 21 kids who ate the same number of calories but from different sources. They concluded that the type of calories consumed influences the number of calories burned . As a second example, we’ve already discussed how adding nuts to the diet can actually aid in weight loss despite the naive calories in-calories out equation. This is a relatively hot topic in nutrition research, and today organizations like the Nutrition Science Initiative (NuSi) are using more rigorous methods to better understand these results [3, 4].
The second problem with the caloric theory of food is that our body doesn’t necessarily digests all the nutrients from foods. A lot of the energy is lost in feces and urine. The first law of thermodynamics holds for isolated systems. This means that the lost energy should be taken into consideration as well. This would be something that is very individual and depends on the fiber content, as well as the gut bacteria of the individual.
To prove my point, imagine drinking one liter of olive oil in one shot. A litter of olive oil contains almost 9,000 calories which is equivalent to one kilogram (or almost 2 pounds) of fat. Now do you really think you will gain two pounds of weight if you do so? Of course not. The most you are going to get from this is a very unhappy stomach (needless to say – please don’t try this at home).
For this reason, Nutrino does not emphasize calorie counting. We recommend focusing on fresh whole foods and to eat in moderation instead of counting calories. For more specific recommendations, please download the Nutrino app.