Typical example is lactose intolerance caused by lactase deficiency. It is an acquired intolerance, rarely congenital. Sometimes, for example, after a food poisoning, there can be damage to the intestinal villi where the lactase enzyme is found causing a deficiency. Lactose intolerance causes abdominal pain, diarrhea, bloating due to hydrogen production. It is easily diagnosed through the Breath Test which measures the amount of hydrogen produced by bacterial fermentation after lactose intake.
The same is the intolerance to sucrose determined by the lack of sucrase.
In other cases, intolerance is congenital like phenylketonuria. Due to a genetic defect the enzyme phenylalanine-hydroxylase is missing. An accumulation of phenylalanine in the blood and in some tissues is thus caused. If the condition is not recognized early, considerable damage may occur. People with this disease should be fed with protein foods free of phenylalanine.
These are food intolerances recognized by official medicine.
In the market there are many tests that try to diagnose food intolerances, from kinesiological to those on blood. But there is still no scientific evidence to prove the validity of these tests. So it is a much debated field where there is a lot of confusion.
In recent times, for example, there is much talk of gluten intolerance, which is very different from the true intolerance represented by celiac disease. In reality it is a sensitivity to gluten that causes symptoms such as abdominal pain, nausea, diarrhea, skin disorders. It has a recurring pattern, that is, it can remain quiescent for some time and then reappear in some periods.
Celiac disease, on the other hand, is a chronic autoimmune disease with a genetic predisposition. Unlike celiac disease there are no specific tests for gluten sensitivity, at least for now. Diagnosis is based on the exclusion of foods containing gluten. The patient generally refers to a certain well-being. This, however, does not exclude the whole percentage of people who can have the placebo effect, ie they improve because something has changed, without that being the real problem.
Eating gluten-free is however a fashion, and many follow it because they are convinced that it makes them lose weight. The “gluten-free” diet is not a low-calorie diet. Gluten does not make you fat.
In the group of intolerances, again according to the European Academy of Allergology, also include pharmacological reactions. In fact there are a number of foods that have pharmacological effects. The most classic example is that of foods rich in histamine and histamine-liberators.
Foods rich in histamine: fermented and aged cheeses, wine, beer, dried fruit.
Histamino-liberating foods: strawberries, chocolate, crustaceans and seafood, egg white, tomatoes.
Another vasoactive substance is the tyramine present in red wine and aged cheeses. In some subjects an excess of these foods can cause urticaria, headache and nausea.
Pseudo-allergies are also defined because the symptoms are similar to those of allergies, however, in which the mechanism is mediated by antibodies of the IgE class.
The diagnosis of adverse reactions to foods requires a very accurate medical history in order to have an overall picture of the patient and then go on to specific tests that particularly concern the field of allergies. These are skin tests such as prick test, prick by prick and patch test and in vitro tests such as total IgE and specific IgE assays. Sometimes there are false negatives despite having a convincing clinical history. In these cases we move to a hypoallergenic diet to be followed for three weeks and we observe the answer.
In the case of non-conventional food intolerances, whose pathogenetic mechanism is not well known, surely a diet from exclusion from food suspected for a short period may be useful to disinfect the digestive system and then proceed to a gradual reintroduction.