Lactose intolerance

Lactose intolerance

Lactose intolerance, or the inability to digest milk sugar, is a disorder caused by the lack of the enzyme lactase.

The milk contains a lot of lactose, which is a sugar, but different from the table sugar. Milk sugar is composed of glucose and galactose. Before passing through the intestinal wall into the blood stream, it needs to be broken in two constituent parts. The process of digestion takes place in the small intestine, with the aid of digestive juices which contain the enzyme lactase. The latter breaks the bond between the two parts, which are then individually absorbed into the blood stream.

Sometimes, there is not enough lactase in the intestine, which causes the lactose to remain undigested. Thus, lactose moves forward into the large intestine, where the bacteria in the intestinal microflora begins to feed on it. The bacteria can break down lactose, but when doing so, they produce a lot of gas as well as other metabolites which stimulate a faster bowel movement. This results in bloating, which can also become painful, gurgling, rumbling in the intestines, and diarrhoea.

What is lactose intolerance?

Lactose intolerance is not an allergy.

Allergy to milk is a different disorder, caused by intolerance to the protein in milk, and exhibits other, sometimes serious consequences. In the case of milk allergy, a repeated complete exclusion of dairy products from the diet is required.

In some exceptional cases, the patient may suffer from both diseases at the same time, so the diagnosis must be always confirmed by a doctor.

Galactosemia is a rare metabolic disorder which is revealed in early childhood. These patients must not drink any milk, not even lactose-free milk.

Basic information about the examination

Locations of lactose intolerance examinations

  • Bled | Pod skalo 4, 4260 Bled
  • Ljubljana | Barvarska steza 4 (Vila Urbana), 1000 Ljubljana
Appointment - referral Appointment - self pay

Frequently asked questions


What kind of problems are caused by lactose intolerance and when?

In the case of lactose intolerance, the ingested lactose cannot break down completely and remains in the lumen of the small intestine. It binds a lot of water and the intestinal contents travel forward into the colon. A part of undigested lactose is excreted, but the other part is decomposed by the bacteria of our normal intestinal flora. During this process, gases (CO2, hydrogen and methane) and short chain fatty acids are produced. The latter are partly used in the intestinal cells. 5-10% of the ingested lactose is excreted with the faeces. Since lactose binds much water, the faeces can be liquid, and some of the produced fatty acids irritate the intestinal mucosa, which results in diarrhoea and possibly leads to unpleasant burning skin inflammation at the rectum.

The activity of lactase in humans declines within a few years after the cessation of breast-feeding. In environments where lactose intolerance is common, the first symptoms emerge already at the age 2-7, while elsewhere the decrease in lactase activity may be delayed until the age 20.

Despite the disrupted decomposition of lactose, some people do not exhibit any symptoms. It appears that this is in part connected to the bacteria species in the large intestine. Different bacteria produce various acids, which may irritate the intestinal mucosa to varying degrees. Also, different bacteria produce a variety of different gases.

The main symptoms of lactose intolerance are, bloating, gases, flatulence, gurgling, increased urinary frequency, liquid stool, and pains, which depend on the sensitivity of an individual's gut.

The amount of ingested lactose affects the severity of the symptoms.

Avoiding lactose is of course necessary only when unpleasant symptoms ensue because of it. The fact is that the ingestion of lactose does not cause any long-term health damage or dangerous acute consequences even in those people who are unable to digest it.

The easiest way is, of course, the home test. If you have problems that are consistent with lactose intolerance symptoms (bloating, gas, diarrhoea, etc.), try to completely avoid milk for a week. After a few days, the problems should subside. After a week, drink half a litre of milk in the morning, on an empty stomach, and observe. If you end up at the toilet, this is already an almost reliable evidence that milk has an adverse effect on you. On the next day, repeat the same test with lactose-free milk, after which you should have no problems.

Home test is the most practical and the easiest to perform, but also the least reliable. Often, it is not enough to remove from our diet just milk, because lactose can be also found in many processed food products. If during the trial diet lactose is not removed from our menu entirely, the problems do not pass and we continue to falsely believe that the symptoms are not related to lactose. On the other hand, the re-occurrence of the problems after you introduce the milk back to your diet is not unique to lactose intolerance, but it may also apply to other disorders, for example, to milk protein allergy.

Today, as a rule, we carry out several different laboratory tests to diagnose lactose intolerance.

The most widely used is the blood lactose tolerance test, for which you can make an appointment with the doctor. On an empty stomach, in the laboratory the patient ingests a test meal with lactose. Then, the patient's blood is collected several times in a row and the increase in blood glucose is monitored. If the at a given time glucose does not increase sufficiently, this proves that lactose has not been broken down and absorbed into the blood stream. Blood lactose tolerance test is most easily accessible, but only measures your blood sugar, which is not always associated with the patient's problems. The blood glucose levels depend on other factors as well, so can many times this lead to false-positive or false-negative results.

At Diagnostic Centre Bled we prefer to use hydrogen breath test, which is also the world's most renowned test to confirm the diagnosis. On an empty stomach, the patient ingests the test amount of lactose, and then exhales into a special bag for 4 hours, once every half hour. The exhaled air is analysed for determining the level of hydrogen and methane. If a bacterial fermentation of lactose occurs, the resulting gases are partially excreted through the lungs and are present in the breath. Therefore, if the exhaled air contains a characteristic increase in these gases, we know that lactose has not been broken down completely.

Hydrogen breath test is the most sensitive among simple laboratory methods. Its usefulness is significant also due to the fact that it allows us to measure the actual production of gases which cause problems for the patients.
At Diagnostic Centre Bled adults can undergo an examination as self-paying clients, without a referral from their physician. For more information and making an appointment please call our appointment scheduling service.
More technologically demanding and expensive is the 13C-lactose breath test, where following the same principle, a marked increase in the exhaled CO2 is monitored.

In recent years there is also the possibility of genetic testing, but is more suitable for research purposes. Several genetic variants have been identified and associated with primary lactose intolerance. Such genes can be determined with rather expensive laboratory blood tests of blood or other body tissues. The disadvantage of these tests lays in the fact that they do not prove or disprove that a disturbed digestion of lactose is really causing problems to the patient, as this is largely dependent on other factors, for example, the composition of intestinal microflora.

If an endoscopic examination of the upper gastrointestinal tract (gastroscopy) is indicated due to the patient's symptoms, we may also take a sample of the lining of the small intestine and, under specific conditions, sent it to the laboratory, where they will be able to directly determine the activity of the enzyme lactase. If the latter is reduced, the patient cannot digest lactose properly.

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