The aim of this paper is to identify, if any, a relationship between obesity and food intolerances, it does not discuss their general veracity and does not question their potential role as a cause or contributing cause of pathological conditions or symptoms of different nature. The writer acknowledges that many people undergo such tests and that their main motivation is mainly to identify if the cause of their overweight is intolerances.
The facts
With the studies of Lavoiser, dating back to the second half of the 18th century, the foundations were laid for the current knowledge on bioenergetics. Today we know that in animal organisms there is a perfect conservation of energy. The heat developed in vivo by a subject is equal to that which the food it has ingested produces by burning in a calorimetric bomb 1 .
During life, every part of our body is subjected to a continuous material exchange. The processes that lead to the synthesis of new structures occur at different speeds depending on the tissue we are considering. With food we take in the nutrients and energy necessary to ensure that the aforementioned repair and synthesis processes take place regularly.
When we absorb energy and nutrients in sufficient quantities to meet our needs without accumulating body fat, we are in a condition that we define as energy balance and the weight remains stable 2 .
If the absorbed energy exceeds the metabolic needs ( positive energy balance ), the excess fraction is accumulated in the adipose tissue and the body weight increases. Conversely, when our energy needs are not met ( negative energy balance ), the body to meet its demands demolishes the reserve fats, an event that can manifest itself with a reduction in weight.
Our body is able to extract energy from proteins, carbohydrates and fats. We know that in the bonds that hold together the atoms of the aforementioned molecules there is an amount of energy available for humans equal to 4 kilocalories per gram of carbohydrates, 4 kilocalories per gram of protein and 9 kilocalories per gram of fat. For the purpose of our reasoning we must underline and remember that the value of these energy coefficients is independent of the food we use to feed ourselves . For example, from 10 grams of fat contained in cheese our cells are able to extract the same energy (90 kcal) that they would extract from 10 grams of fat contained in soy or any other food.
Our organism has no reserves of proteins or carbohydrates (we deliberately neglect the glycogen content – the storage form of glucose in animal cells – which is irrelevant for the purposes of our discussion because it is potentially responsible for modest weight changes). If consumed in excess, proteins and carbohydrates are transformed into fat and only subsequently used as a source of energy ( fat in human tissues also provides 9 kilocalories per gram ).
All the energy transformation processes described above occur with different efficiency from subject to subject. The returns of the metabolic pathways and their intrinsic characteristics depend on a multitude of factors that are not subject to our voluntary and conscious control.
Some reflections
We come at this point to the initial question: What role can food intolerance play in this context?
Proponents of the causal role of food intolerances in weight gain, as far as I know, do not explain it. But even in the event that these immunological and extraimmunological mechanisms that should be at the basis of food intolerance reactions are not known but only hypothesized, those who support this cause-effect relationship should agree with the writer that a reduction of energy requirements following the intake of non-tolerated foods.
If it were really intolerance to foods to determine the deposition of body fat, in higher quantities than when the same foods are absorbed by a non-intolerant subject, we should demonstrate a link between metabolic efficiency and food intolerance. All other conditions being equal (quantity of food and level of physical activity) the energy contained in a food should be deposited in the adipose tissue of intolerant subjects with greater efficiency than in non-intolerant subjects.
In reality, the articles on food intolerances that I have had the opportunity to read do not address the subject in these terms and do not demonstrate what has been argued above, they simply claim that in some subjects obesity is associated with food intolerances .
In some publications, however, this link does not even emerge, it is the case of a book written by two American doctors (one of which is a member of the Clinical Ecology Society) and by a scientific journalist. It lists the signs and symptoms that may indicate reactions of sensitivity to food, but the word obesity does not appear in that list .
Finding a relationship between two quantities does not necessarily mean proving that there is a cause and effect relationship between the two variables. For example, in industrialized societies there is a correlation between childhood obesity and hours spent watching television, but it would be superficial to conclude that television is the cause of obesity.
A not too thorough analysis leads us to easily demonstrate that children watching television, sitting in an armchair, eating French fries and other foods rich in fat, easily achieve a positive energy balance. If the kids watched TV on exercise bikes or eating lettuce and drinking just water, things would probably be different.
A recent study shows that regular consumption of pizza can counteract the onset of various types of cancers of the digestive system. However, the authors state in an interview that eating pizza can simply be an indicator of healthy eating. In fact, it would be difficult to argue that eating pizza regularly without observing the other indications provided by the main agencies for the study and prevention of cancer represents a valid strategy for not getting cancer.
Thus, similarly to pizza, obesity in subjects who also show a food intolerance, simply represents an indicator of an overall unbalanced and excessive diet. The alterations and metabolic imbalances, of which obesity is the tangible sign, could also manifest themselves with a positive response to some laboratory tests, normally used to assess the level of intolerance to food, but this cannot lead us to conclude that the intolerance to food is the cause of excess weight.
At this point, let’s try to imagine a hypothetical scenario, in which two subjects, A and B, with A intolerant to food X, eat the same amount of the suspect food. Let’s assume that the energy contained in it is 1000 kcal and sufficient to create in both a condition of energy balance according to the definition made above.
Considering that it is not possible to create energy, arguing that food X is responsible for the deposition of fat in subject A means arguing that the interaction of X with A induces a positive energy balance through the reduction of energy expenditure, an event that never is. been observed and demonstrated. On the contrary, we have known for about a century that an increase in basal metabolism can be observed following food intake.
It is evident that the hypothesis that the ration X is excess for both does not make sense to discuss it, in that case the deposition of fat would be true for both subjects and certainly determined by the positive balance achieved.
So far we have hypothesized that the absorption of food is potentially not tolerated. If, on the other hand, as in the case of the intolerances we know, the nutrients were not absorbed, they could not provide energy. In this case, to justify the deposition of body fat we should necessarily argue that following the interaction of the food with the intestinal wall, mechanisms are activated that can reduce the energy requirement and start all those metabolic pathways capable of transforming the other available nutrients (proteins and carbohydrates) effectively removing them from their main functions 3 .
A similar mechanism appears very unlikely and even the evolutionary interpretation is not convincing. What evolutionary advantages would determine the synthesis and deposition of fat when the organism does not absorb nutrients?
In reality, the data in our possession and more simply the daily experience, prove exactly the opposite. In the absence of food and therefore of nutritional absorption, mechanisms are activated that lead to the demolition of fats in adipose tissue. In fact, the existence of what is now more correctly defined as adipose organ is explained precisely by supporting its very important task as a source of energy in periods of food shortage.
Obvious conclusion
I would like to conclude by responding to the many who wonder why relatives and friends lose weight after having undergone food intolerance tests and eliminating suspicious foods. For an obvious reason, the elimination of commonly used foods results in a significant reduction in nutrient intake, making the energy balance negative. That’s all. I also believe that essential components in these dynamics are those of a psychological nature (how could it be otherwise?): It is easier to take it out on some food and trace the cause of our excess weight to it, rather than investigating more deeply and questioning our own lifestyle to understand what are the real reasons that end up making us take more food than is necessary for us, unique true proven cause of body fat gain.
