Understanding Lactose

A lactose-free diet is becoming an increasingly common eating pattern for many, with lactose-free and plant-based alternatives to regular dairy products gaining popularity and becoming more readily available. This raises the question: should everyone be restricting or completely eliminating lactose from their diets? The internet is brimming with questions surrounding if, when and by whom lactose should be avoided. There is also confusion as to whether lactose is only present in dairy products? And, furthermore, how to find out if someone is lactose intolerant? Many people who are not able to digest lactose have no symptoms at all, whilst others experience very uncomfortable symptoms. It is therefore helpful to know how to recognise a lactose intolerance and how to manage it. 

What is lactose?

Lactose is a natural, large sugar molecule made up of glucose and galactose, that is mainly found in milk from mammals. Lactose represents approximately 6% of the carbohydrates consumed in Western diets and, although we often only associate lactose with dairy products, this sugar is also commonly used in a wide range of products, including: baked goods, breakfast cereals, drinks and even processed meat. 

Lactose in whey has become the focus of attention more recently, as studies have shown that it serves not only as a source of energy, but also as a key player in facilitating the absorption of calcium, phosphate, manganese and magnesium. In addition, when undergoing fermentation in the gut, lactose contributes to the development of healthy gut bacteria, which are important for immune health.

Sometimes lactose is falsely blamed for gut complaints – so it is important to note that by eliminating lactose-containing products  from the diet without having to, we could miss out on the health-promoting components that lactose provides. This is also why those that are lactose intolerant should try to avoid completely eliminating lactose-containing products but to simply reduce lactose consumption, or opt for equally nutritious alternatives.

Lactose intolerance explained

Lactase is the enzyme that plays a fundamental role during lactose digestion, which takes place in the small intestine. More specifically, this enzyme is responsible for splitting lactose into glucose and galactose, allowing its absorption by the intestinal cells. Around 70% of the population worldwide has lactase deficiency. Without the lactase enzyme, the undigested lactose becomes subject to bacterial fermentation, which leads to lactose malabsorption. 

There are three types of lactose intolerance: congenital, primary, and secondary lactose intolerance. Congenital lactose intolerance is very rare, with symptoms that can appear shortly after birth and may last throughout the entire lifespan. In this case, it is crucial to recognise the intolerance early in infancy, to avoid the risk of dehydration and subsequent life-threatening consequences. Primary lactose intolerance occurs more frequently and is caused by a decrease in the lactase enzyme after the age of 2. Lastly, secondary lactose intolerance is linked to reduced lactase activity due to diseases such as infections, food allergy, celiac disease, Crohn’s disease, or radiation/chemotherapy-induced enteritis. In this case, the symptoms may disappear only once the primary disease is treated. Depending on the origin of the condition, doctors may suggest different kinds of treatments.

As mentioned, not everyone suffers from gut complaints due to the malabsorption of lactose. 

However, if after ingesting it in high quantities you are experiencing symptoms such as abdominal pain, bloating, flatulence, diarrhea and headaches, there is a higher chance that could be caused by lactose intolerance. There is no standard timeframe for lactose digestion; it may take 12 hours, 24 hours, or even 72 hours to fully eliminate the lactose-containing food. However, studies indicate that the symptoms could peak 5-10 hours after the consumption of lactose.

In order to confirm the diagnosis of lactose intolerance, clinical tests such as the hydrogen breath test, a genetic test or a small intestinal biopsy can be performed. Among the three, the least invasive and most cost-effective procedure is the hydrogen breath test, which is generally used to detect gastrointestinal disorders. The hydrogen breath test detects traces of hydrogen on the breath following milk consumption, which is indicative of lactose malabsorption in the gut – and therefore lactose intolerance.

Lactose intolerance vs cow’s milk allergy

Lactose intolerance can often be confused with cow’s milk allergy, which may then lead to unnecessary dietary restrictions. Therefore, it is important to know what the major differences between a lactose intolerance and a cow’s milk allergy are.

As discussed, lactose intolerance results from a reduced ability to digest lactose, which is a sugar. On the other hand, cow’s milk allergy is caused by an immune-mediated reaction to the proteins contained in milk. While lactose intolerance causes milder symptoms, cow’s milk allergy can affect the respiratory system and cause more aggressive reactions (e.g. signs of anaphylaxis), even after cow’s milk proteins are consumed in microscopic amounts. Whereas for lactose intolerance it may only be required simply to reduce lactose intake, for a cow’s milk allergy it is necessary to strictly eliminate cow’s milk from the diet altogether. 

Managing lactose intolerance

There is no specific treatment for lactose intolerance, as it depends largely on the origin of the condition. The main principle is to either reduce lactose consumption or increase lactase enzymes available to digest it. 

If you suffer from lactose intolerance, the following tips can help:

  • Consume no more than 10-15g of lactose per meal (this is equal to 240ml cow’s milk). In case of non-congenital lactase deficiency, most people can tolerate this amount throughout the day
  • Consume lactose-containing foods together with other food, as this will help to dilute the lactose content. 
  • Only consume lactose-containing products at every other meal, as this gives the gut more time to process the lactose in the meantime. 
  • Consume more lactose-free dairy products or plant-based alternatives. Some lactose-free milk and cheeses are produced by adding lactase enzyme to milk, which predigests the lactose. Generally, these products are widely tolerated but they do tend to have a sweeter taste compared to regular dairy products. 
  • Increase the presence of lactase in the small intestine. By doing that, symptoms significantly reduce because of proper breakdown of lactose. This can be achieved with the consumption of lactase in the form of tablets or drops. Moreover, this can really allow a non-restricted diet, which is also a benefit to take into consideration. In addition to that, lactase drops can even be added to breast milk to ensure that infants obtain all necessary nutrients. 
  • For patients with congenital lactose intolerance, the safest option is typically adherence to a completely lactose-free diet. When on a strict lactose-free diet, a person must carefully check all food labels not only on dairy products but also on non-dairy foods such as bread or processed meat. It is also important to ensure a balanced diet with no nutritional deficiencies.
Impact of a lactose-free diet

Overall, a lactose intolerance is not harmful for most, but it can be a cause of discomfort in the long term if not managed. Lactase supplements can really help to provide freedom with foods, but these are more often seen as an occasional option rather than a long term solution. It is generally up to the individual how to best balance food choices and quality of life. For both congenital and non-congenital lactose intolerant individuals, opting for a diet in which lactose-based products are limited or, in extreme cases, completely eliminated is the main approach to management. 

For anyone living with lactose intolerance who is looking for healthy and tasty lactose-free recipe inspiration, Swapmeals provides a great resource for delicious and nutritious meals! 

Links to lactose free recipes



This information does not serve as dietary advice and is not a replacement for medical guidance. It is always recommended to consult a dietitian when you suffer from congenital and non-congenital lactose intolerance.


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