It is very common for patients to relate certain symptoms to the ingestion of certain foods. This may be due to various reasons: sometimes it is the consequence of a genuine food allergy, sometimes it is due to malabsorption of certain carbohydrates, in many cases it is an intolerance to certain foods, and – often – it is just the result of chance.
In this regard, it should be remembered that a food allergy is defined as the immunological response induced by the proteins of certain foods. It is distinguished from food intolerance (which is much more frequent) because the latter is a non-immunological reaction produced by the constituents of certain foods such as toxins or pharmacological agents (e.g. caffeine). On the other hand, malabsorption is the defect in the absorption of nutrients from the intestinal lumen into the lymph or blood, and the term maldigestion is reserved for cases in which intestinal absorption is impaired as a result of a deficit of certain digestive ferments.
The dreaded lactose
Lactose malabsorption is caused by lactase deficiency in the intestinal mucosa and can be congenital or acquired. It is important to remember that there is a poor correlation between lactase deficiency and clinical manifestations. There are important racial differences in its incidence. Thus, in white adults in northern Europe it is 5%, in Spain 15-30%, and in black Americans, Bantus and Oriental races 60-90%.
Other sugars: fructose and sorbitol.
Sorbitol and fructose are sugars that are present – in different proportions – in fruit and are also used as sweeteners in beverages, jams, diet and diabetic products. Large amounts of sorbitol cause diarrhea even in healthy subjects.
Diagnosis
To establish which foods produce a food allergy, it is necessary to perform specific blood tests and, frequently, skin provocation tests.
There is no test that is truly useful for establishing food intolerances (“which foods are bad for you”). There is insufficient scientific data to show that blood tests for immunoglubulin G (IgG) are useful. The most effective and simplest test for the diagnosis of food malabsorption is the breath test. It consists of obtaining samples of exhaled air (by blowing) after administration of a known amount of the carbohydrate to be studied (lactose, fructose, sorbitol, etc).