It is very common for patients to associate certain symptoms with the intake of some foods. This fact can be due to several reasons: sometimes it is the consequence of an authentic food allergy, in others it is due to a malabsorption of certain carbohydrates, in many cases it is an intolerance to certain foods, and - often - it is only the fruit of chance.
In this respect it is necessary to remember that the immune response induced by the proteins of some foods is defined as food allergy.. It is distinguished from food intolerance (which is much more frequent) because this is a non-immunological reaction produced by the constituents of some foods such as toxins or pharmacological agents (for example caffeine). On the other hand, malabsorption is the defect in the absorption of nutrients from the intestinal lumen to the lymph or blood, and the term maldigestion is reserved for cases in which the intestinal absorption is altered as a result of the deficit of certain ferments digestive
The dreaded lactose
L lactose malabsorption is caused by lactase deficiency in the intestinal mucosa, and may be congenital or acquired. It is important to remember that there is a poor correlation between the deficit of lactase and clinical manifestations. There are important racial differences in their incidence. Thus, in white adults of northern Europe it is 5%, in Spain 15-30%, and in black Americans, Bantu and oriental races of 60-90%.
Other sugars: fructose and sorbitol
Sorbitol and fructose are sugars that are present - in different proportions - in the fruit and are also used as sweeteners for drinks, jams, dietary products and for diabetics. Large amounts of sorbitol cause diarrhea even in healthy subjects.
To establish what foods produce a food allergy it is necessary to make specific blood tests and, frequently, provocation tests on the skin.
There is no evidence that is truly useful to establish food intolerances ("what foods feel bad"). There is insufficient scientific evidence to show that blood tests for immunoglobulin G (IgG) are useful. The most effective and simple test for the diagnosis of food malabsorption is the breath test. It consists in obtaining samples of expired air (blowing) after the administration of a known quantity of the carbohydrate to be studied (lactose, fructose, sorbitol, etc).