In most cases, such sensations are associated with lactase deficiency, a violation of lactose absorption. Why is this happening?
What is lactose and how is it absorbed?
Milk and dairy products contain a carbohydrate called milk sugar (lactose). It consists of two molecules: glucose and galactose. When lactose enters the small intestine, it must break down into separate glucose and galactose molecules in order to be subsequently absorbed through the intestinal wall. This cleavage is possible only with the help of an enzyme called lactAse. With age, lactase activity gradually decreases, because dairy products cease to be an obligatory part of the diet (unlike infants and young children, for whom milk is the main food).
If the body lacks the enzyme lactase, the undigested lactose passes from the small intestine to the large intestine, attracting water with it. In the colon, under the influence of bacteria, it ferments to form gas and lactic acid. As a result, bloating, loose stools, nausea, or even abdominal pain may occur after eating dairy products. However, some of the lactose still manages to break down in the small intestine, which explains why small portions of dairy products are better tolerated (there is enough enzyme to process them). But if you eat or drink too much, the body will no longer have enough lactase to break down all the lactose, and then unpleasant symptoms will appear.
Genetic factors and enzyme activity
Lactase activity is regulated by two genes: MCM6 and LST. The MSM6 gene affects the function of the LST gene, therefore, depending on the MSM6 genotype, several variants of the lactase enzyme activity are distinguished.:
C/C genotype: low activity of the LST gene, associated with lactose intolerance.
C/T genotype: lactose intolerance may occur at an older age; the most common variant.
T/T genotype: high activity of the LST gene in adults, providing good lactose digestibility.
Secondary lactase deficiency can develop temporarily against the background of gastroenterological diseases, after damage to the villi of the small intestine (for example, with inflammation or after intestinal infections), as well as due to operations on the stomach and intestines. In these cases, the lactase enzyme is not enough for the duration of illness or rehabilitation. When the villi are restored, dairy products are tolerated normally again.
Congenital lactase deficiency is extremely rare (in newborns).
You can avoid the appearance of unpleasant symptoms by reducing the amount of dairy products consumed or temporarily eliminating them from the diet and monitoring your condition. But it is important to remember that milk and dairy products are very valuable components for the body.
Why eat dairy products?
Milk and dairy products are an excellent source of calcium, which is essential for the formation and maintenance of bone tissue. Calcium deficiency often leads to osteoporosis: bones become brittle, which increases the risk of fractures, especially in the elderly and menopausal women. It is worth thinking about bone health in childhood and adolescence, unjustified refusal of dairy products or unjustified restriction of them can negatively affect the condition of bones in the future. In addition, calcium is involved in the transmission of nerve impulses and muscle contraction. The daily requirement for calcium is 1000-1200 mg, and one glass of milk contains about 240 mg. Milk also contains important amino acids, saturated fats, and vitamins. "Alternative milk" is different in composition from cow's milk and usually does not provide such a variety of vitamins and minerals.
How much lactose can I consume?
Even with the C/C genotype (low lactase activity), many people can tolerate small amounts of lactose. In such cases, products with a low lactose content are suitable. Sometimes a person can easily tolerate the use of small portions of dairy products. For example, an average of 10-12 g of lactose per day (about one glass of milk) is tolerated without any problems. Fermented dairy products and hard cheeses are usually the best digested. It should be noted that skimmed milk may contain more lactose than regular milk. There are also special enzymes (lactase in drops or tablets) that can be added to dairy products before consumption. They break down lactose and help to avoid unpleasant symptoms.
Below is a table with the approximate lactose content in various dairy products:
Hidden sources of lactose
In addition to the obvious "dairy" products, lactose can be found in bread and pastries, dry mixes for sauces and breakfasts, ready-made baking mixes, freeze-dried foods, and breakfast cereals.
Methods for the diagnosis of lactase deficiency
It is possible to suspect lactase deficiency by characteristic complaints after eating dairy products. Doctors often recommend eliminating the "milk" for a while, and then reintroducing it into the diet in order to track which portions and types of foods cause unpleasant symptoms.
The "gold standard" of diagnosis is the determination of the activity of the lactase enzyme in the small intestine (during biopsy during gastroscopy). Genetic analysis and a hydrogen breath test after a lactose loading dose also help in the diagnosis.
Thus, dairy products do not always need to be completely eliminated: it is often enough to reduce their quantity or choose the right type of "milk". If the symptoms are severe, it is worthwhile to consult a doctor and undergo a diagnosis in order to find the best way to preserve valuable nutrients in the diet and at the same time not suffer from discomfort.