Lactose intolerance: what is lactose intolerance?

Feeling full, flatulence, abdominal cramps, diarrhea, or even vomiting after consuming milk or dairy products indicate what is known as lactose intolerance, the intolerance to milk sugar.

Lactose intolerance

Discomfort occurs in those affected when lactose enters the colon undigested. There it is broken down by bacteria into lactic and acetic acid and intestinal gases (hydrogen, carbon dioxide). When consuming milk and dairy products, this leads to gas, abdominal pain, and diarrhea, depending on their sensitivity.


Have you ever heard of the term lactose intolerance? Most likely. In medical terminology, this property is known as lactose intolerance. However, one only speaks of lactose intolerance when symptoms actually occur.

“The reason for this is a deficiency or lack of a digestive enzyme, lactase. The intolerance usually occurs in later years of life, as the tolerance of lactose decreases with age due to the rarer milk consumption. But it can also be innate, ”says Dr. Christian Feinböck from the Austrian Red Cross.

The severity of the complaints varies greatly. Some sufferers get severe discomfort even with the smallest amounts. Usually, however, small amounts of lactose are well tolerated. 10% of Germans have lactose intolerance, and in Africa and Asia, it even affects 90% of the adult population. But what is lactose intolerance, and what symptoms can lactose intolerance cause?

What is lactose intolerance

In the case of lactose intolerance (also known as milk sugar intolerance, carbohydrate malabsorption, lactose malabsorption, or Anastasia), the milk sugar (lactose) ingested with food is not digested properly as a result of the lack of or reduced production of the digestive enzyme lactase.

As an infant, there should be no negative symptoms during breastfeeding, as the child independently produces lactose. The lactase enzyme is produced by all mammals when they are breastfeeding; it splits milk sugar into the sugars galactose and glucose used by humans.

The organism cannot absorb milk sugar, only its building blocks. The enzyme lactase breaks down the milk sugar into these components. If lactase is missing, the milk sugar is not broken down and causes the symptoms.

If unsplit lactose reaches the large intestine, it is absorbed and fermented by intestinal bacteria. This so-called fermentation creates additional gases, and more fluid flows into the colon. The fermentation products lead to flatulence and osmotic diarrhea (diarrhea).

Digestion with lactose intolerance

After the breastfeeding process is stopped, the lactose level in the child’s body also drops, and lactose production is stopped. In many people, this can happen without major side effects, and only in a population that has been exposed to the consumption of cow’s milk for decades, there was a natural mutation. This also explains why almost 90% of the African and Asian populations have suffered from lactose intolerance to date.

How do you get lactose intolerant?

Basically, our digestive system switches to processing other foods when we are weaned from milk as children. The body then produces significantly less lactase and can, therefore, only break down smaller amounts of lactose. It is a completely natural process.

If this happens in excess after weaning, one speaks of physiological lactase deficiency, with lactase activity decreasing towards zero with increasing age. Most of the time, lactose intolerance develops in adolescence and early adulthood.

This form is also known as primary lactase deficiency and is common worldwide.

But there are also regional differences. In Asian countries, for example, most people completely lack the enzyme to break down lactose. This is why there are practically no milk or cheese products on the menu in these regions. Overall, it can be expected that around 90% of the world’s population will no longer be able to utilize lactose after infancy fully. However, this does not necessarily mean that all those affected suffer from symptoms.

In the case of secondary lactase deficiency, however, the lactase deficiency is the side effect of another disease such as celiac disease or Crohn’s disease. For this reason, this form can occur at any age.

What are the symptoms of lactose intolerance?

Constant feeling of fullness, flatulence, abdominal cramps, (watery) diarrhea, or vomiting after consuming milk or dairy products are clear indications of lactose intolerance. Lactose intolerance usually leads to symptoms after a few minutes or a few hours after consuming milk and foods containing lactose.

Because the lactase activity is reduced or completely stopped in this way, the lactose reaches the human colon without being split. The fermentation there produces lactate and gases. These, in turn, lead to the flatulence we know. The lactic acid that has reached the intestine activates the influx of water and ends in watery diarrhea. But people with lactose intolerance also report headaches, tiredness, depressive moods, or dizziness.

Diagnosis: test lactose intolerance

How do you know if you are lactose intolerant? You can quickly and inexpensively determine this by performing a self-test.

Stay away from any dairy product for several weeks. Document whether any common symptoms are absent, such as diarrhea mentioned above or other symptoms that you may have associated with dairy consumption in the past.

After about 14 days, you do the self-test and drink or eat a product containing lactose. If the listed properties reappear, you can assume that you are lactose intolerant. But be careful: Such self-tests cannot always be accurate.

It is still best that you have your trusted doctor test you for intolerance. If there is only partial intolerance, it can often happen that people do not show any symptoms.

There have long been two simple diagnostic procedures that can be used to easily detect lactose intolerance: a blood test (blood sugar test; lactose tolerance test ) and a breath test.

Lactose intolerance is usually diagnosed using an exercise test. Milk sugar is dissolved in tea or water, drunk, and then increased blood sugar is measured. Another test also involves drinking lactose and then measuring the hydrogen content in the breath.

This so-called H2 breath test (hydrogen breath test ) is currently the standard procedure for detecting lactose intolerance. A tissue sample taken from the intestine can also be examined for lactase activity in more difficult cases.

Is lactose intolerance a “disease” of the 21st century?

In the last decades, numerous media have reported that lactose intolerance is a “disease” of the 21st century. But this is incorrect information. Even our ancestors in the Neolithic period suffered from it. How do you know this? Do you remember the iceman? Ötzi, a mummy discovered by chance in 1991 on the Ötztal Glacier between Austria and Italy, let this theory fall to thin air.

Experts were able to prove that this ice-cream man was already lactose intolerant. This proves that humans were never intended to consume cow’s milk in any form. But it also shows that a mutation must have taken place in the genes of individual strains at some point. This explains why only 10% of the German population suffers from it.


“The recommended therapy is to avoid dairy products and compensate for the lactase deficiency with medication. However, careful re-acclimatization of dairy products is also a therapeutic option, as completely avoiding milk or dairy products has disadvantages.

Milk contains several necessary nutrients, such as calcium and vitamin D. If too little calcium is absorbed, the bone substance decreases faster. Calcium supplements must be administered after consulting the doctor, ”says Feinböck.

The lactose content of certain foods

  • Soy products, vegetable milk powder, and margarine are lactose-free.
  • Almost lactose-free (less than one gram of lactose / 100 grams) are: e.g. butter, rice, coconut and oat milk, hard, semi-hard, and soft cheese.
  • Curd cheese, cottage cheese, sour milk and cream, buttermilk have a medium lactose content (one to 4.5 grams of lactose / 100 grams)
  • Have a higher or high lactose content (over 4.5 grams lactose / 100 grams): e.g. milk, whey, curd milk, condensed milk, kefir, yogurt, curd cheese, and whipped cream.

Replacement products

Anyone who has to omit milk as an important supplier of calcium needs a substitute. For many of those affected, plant-based soy milk products can be used as a substitute for cow’s milk. They are made from soybeans and are high in protein, essential amino acids, iron, and vitamins.

There is now a whole range of products based on soy milk: for example soy sausage, soy pudding, terrines and spreads, soy yogurt, or soy quark (tofu). Products made from tofu can be used as a substitute for cheese and meat. You can get them in health food stores and health food stores, but also in many supermarkets.

The mineral is also contained in soy milk, but in significantly smaller quantities than in cow’s milk. Green vegetables like broccoli, kale, and spinach are good sources of calcium. In the case of fruits, many berries and kiwis contain higher amounts of calcium. There are also mineral waters that are particularly rich in calcium and contain more than 15 milligrams of calcium per 100 milliliters.

In addition to soy milk, almond, oat, coconut or rice milk can also be used as a cow’s milk substitute, especially for desserts .

Tip: It is interesting to know that e.g. B. Butter contains practically no lactose, whereas most margarine contains it, that the dairy product cheese does not automatically have to have a high lactose content (e.g. Emmentaler or Parmesan contain little lactose), or that some yogurts with “active cultures” contain an enzyme for lactose digestion.

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