It is the first data that we usually observe in the labeling of the foods we consume and for many, it is of great importance if we seek to obtain how much energy we consume every day. So, we ask ourselves, how are calories calculated from food?
Kilocalories and non-calories
Although we are accustomed to talk about calories, the truth is that we should always always name the kilocalories that are what we actually consume and spend.
In food labeling we can see your energy intake indicated in kilocalories per 100 grams or per serving and a kilocalorie (1000 calories) represents the thermal energy needed to increase the temperature of one gram of water by one degree centigrade to a normal pressure Of an atmosphere.
Thus, foods indicate the amount of energy they offer in terms of kilocalories and our body burns in equal energy.
How are calories calculated from food?
The method used traditionally to know the calories that a food has, or rather, the kilocalories of it, consists in the use of a calorimeter, by means of which the production of heat of a product is evaluated directly, and thus, it is estimated energy supply.
However, there is also indirect calorimetry that measures gases that are eliminated by burning a food.
At present, as food manufacturers not only must notify the calories that offer their products but also the nutrients of the same, uses the method of the scientist Wilbur Atwater, who through a special calorimeter averaged the energy input of the different nutrients we consume For more than 100 years.
Thus, it is known that proteins and carbohydrates offer 4 kilocalories per gram, fats 9 kilocalories per gram and alcohol 7 kilocalories per gram. With this data, the total kilocalories of each product is estimated and the energy value reported in the labeling is obtained.
Then, by means of a calorimeter or by using tables that determine the calories of each ingredient that makes up a food, we can obtain the final kilocalories of a product. With this last method we can also estimate the energy input of our dishes, using databases such as the US Department of Agriculture with information of more than 6000 foods.
Generally, the food industry standardizes its processes and therefore, evaluates by calorimetry only one food to determine the energy offered per 100 grams and then per serving.
Are these calculations accurate?
Although the calorimeter clearly gives reliable results on the kcal content of a product, the reality is that since neither product is equal to another and that no organism metabolizes food in the same way as another, the calculations can be very imprecise .
The amounts of each ingredient that is incorporated into a food or dish can vary from one to another considerably, as does the final weight of the product, which may give rise to calories very different from those declared.
On the other hand, the Atwater method does not consider the process of each food in our organism, that is, we do not consider what our body metabolizes, burns to digest and finally absorbs, so there is one more factor that can modify the Calories we eat.
A study published in the British Journal of Nutrition made with pistachios showed that these offer our body 5% less of the calories that are determined by the method currently used.
This difference that can overestimate the calories of the healthiest foods is due to the fact that our body finally metabolizes less energy than a product actually brings, because it has, for example, a high amount of fiber or resistant starch than the body Human can not fully digest or absorb .
So the calories are determined with a method that at present, is not yet the most adequate or accurate and will never be if we think that there are organisms that digest more or less than others as well. Therefore, basing our diet or our choices only on calories is a serious mistake.
In fact, not all calories are the same for our body because depending on the nutrients they provide they can be more or less recommended and have different effects on the human body.
Then, when choosing what to eat or what ingredients to elaborate our dishes, we can observe the energy input stated in the labeling but also, it is important to look at other factors such as the nutrients that make up the food.