Lactose intolerance: myths and misconceptions

Dairy products have become almost impossible to imagine away from most menus: a bowl of muesli with milk in the morning, a nice slice of bread and butter with cheese in the evening, and with the latte in between there is a little piece of strawberry cake with cream. For around 70% of the world’s population, however, that is unthinkable, because they cannot digest the milk sugar lactose and suffer stomach ache and diarrhoea after a latte. With that impressive figure, lactose intolerance is the most common food intolerance in the world. No wonder, then, that many myths and half truths surround it. We have taken a closer look at the most common ones and explain what we are really dealing with here.

Lactose, also called milk sugar, is a naturally occurring component of the milk of all mammals. So besides cow’s milk, sheep’s and goat’s milk and even our own human breast milk contain lactose. It is made up of two sugar components and is meant to serve our offspring as a source of energy. So that the babies, calves or lambs can make use of it, they produce the enzyme lactase. Lactase sits on the intestinal lining in the small intestine and takes on the task of splitting the double sugar into its individual sugar building blocks. Only through this splitting does the lactose become small enough to be taken up through the intestinal lining into the body and used.

Unlike all other mammals, we humans still use milk as a food after our time as infants. However, not everyone keeps the lactase needed for this into adulthood, and so it comes about that the milk sugar passes through the small intestine unsplit and undigested and then ends up in the large intestine. In the large intestine, the home of our gut flora, the lactose can be fermented by the bacteria living there. This produces gases, which raise the pressure in the abdomen and can cause unpleasant stomach ache (and unpleasant situations). That is still the lesser evil, though, because if the lactose is not split by the gut bacteria, it draws water into the large intestine and causes diarrhoea. In both cases, eating dairy products brings unpleasant digestive complaints with it and should be avoided by people who are lactose intolerant.

Precisely because so many people are affected by lactose intolerance, half truths and hasty assumptions about the intolerance keep circulating. We have tackled the most common myths and checked how much truth there is in them. Off we go with our myth check!

True and false!

With very rare exceptions (only a few cases are described worldwide), babies are always able to digest and use lactose. The fact that lactase is often lost later and brings an intolerance with it is indeed genetically determined in most cases. But lactose intolerance can also occur as a side effect of other conditions that damage the intestinal lining, for example coeliac disease or viral illnesses. In this case it is called secondary lactose intolerance and fortunately disappears again as the digestive system recovers.

False!

Care is needed here, because besides lactose intolerance, an allergy to cow’s milk protein can also cause digestive complaints after consuming milk. In this case the immune system reacts to certain antigens of the milk proteins and triggers an allergic reaction, which can cause not only stomach ache, diarrhoea and nausea but also skin reactions and breathing difficulties. Those affected are mostly children. Because the symptoms are similar there is a risk of confusion, but the right diagnosis is very important. While smaller amounts of dairy products can be tolerated with lactose intolerance, it is better for people with a milk allergy to do without them completely.

True!

Overall, around 70% of all people in the world are not able to digest lactose, so lactose tolerance is in fact the exception and not the other way round. Between the various parts of the world, however, there are strong differences. Lactose tolerance is most common in northern Europe, North America and Australia. Between 5 and 15% of those populations are affected by the intolerance. In South America, Asia and Africa, by contrast, it is more than 50%, and in some Asian countries almost 100% of the population there. That is also why you look in vain for dairy products in Asian cuisine.

True!

The phenomenon of lactase activity persisting into adulthood first appeared around 10,000 years ago. Even though that period sounds unimaginably long, in evolutionary terms it is rather short. Back then the first of our ancestors began keeping cows as livestock. In the northern regions of the world above all, milk was an important food which, in times of poor harvests, offered a survival advantage to those who could tolerate it. Besides plenty of energy from fat and milk sugar, it also supplied easily digestible calcium, which made a decisive difference especially in less sunny regions with lower vitamin D synthesis. So originally all humans were lactose intolerant.

False!

Some dairy products naturally lose a large part of their lactose in the course of processing. Butter or matured cheeses such as Parmesan or Gouda generally contain only small amounts of lactose. So here you usually do not have to reach for special lactose free products. Various studies on tolerance have also shown that a lactose intake of around 12 g (that corresponds to a glass of milk) spread across the day did not bring on any symptoms in most cases. Fermented dairy products such as yoghurt or kefir are also interesting: they do contain similarly high amounts of lactose as milk, but they bring milk sugar splitting bacteria along with them, which can increase tolerance. That said, every affected person is different and should test out for themselves what they tolerate.

True and false!

It depends on the cause of the intolerance here: secondary intolerance has usually disappeared once the underlying condition has been cured. If the intolerance is genetically determined it cannot be cured, but the symptoms can still be improved. The decisive role here is played by the microbiome in the gut, because with the right bacteria in the gut flora the lactose can be fermented in such a way that less gas is produced and no diarrhoea develops. Taking probiotics, living microorganisms that can spread in the large intestine, is recommended for this. The best preparations are those that contain the species Bifidobacterium animalis: the positive effect has been researched best for this one so far. You can find out more here: Gut flora and the influence of prebiotics and probiotics.