Understanding Lactose Intolerance and Lactase Non-Persistence

Most people enjoy dairy without a second thought- but for a large portion of the population, digesting milk isn’t so simple. Understanding why this happens and how to manage it can help you enjoy dairy without discomfort.

A bit of background 

Lactose is a natural sugar found in milk and most dairy products. It’s made of two smaller sugar molecules, galactose and glucose, which the body needs to break apart before they can be absorbed into the bloodstream. This is where lactase comes in. Lactase is a digestive enzyme produced in the lining of the small intestine that breaks down lactose into smaller sugars. Babies tend to naturally produce high amounts of lactase because milk is their primary food source. 

What are Lactose Intolerance and Lactase Non-Persistence? 

Lactose intolerance occurs when insufficient lactase leads to undigested lactose entering the colon, where gut bacteria ferment it. This fermentation produces gas and draws water into the bowel, resulting in symptoms such as bloating, abdominal pain, gas, nausea or diarrhoea shortly after consuming lactose. 

Whereas lactase non-persistence (LNP) refers to a genetic and developmental pattern in which the enzyme naturally declines after infancy. In most mammals, lactase levels generally fall with age as our bodies stop needing to digest mother's milk as toddlers grow up. At the molecular level, this is associated with changes in how the LCT gene is regulated, not just the DNA sequence itself, but how that DNA is epigenetically modified over time. These changes reduce lactase production and explain why many adults produce low levels of the enzyme.

Many people with LNP don't develop symptoms until they eat more lactose than their stomachs can handle. Lactose intolerance is a clinical syndrome, while LNP is a biological trait that may or may not lead to symptoms. Essentially, you can be genetically non-persistent for lactase and still tolerate some lactose if you consume it in small amounts or with other food. 

What to eat

→ Low Lactose dairy products 

Low-lactose foods mean there is less sugar for the body to break down. For people who produce limited lactase, this reduced lactose load often stays within what their remaining enzyme activity can handle 

When only a small amount of lactose enters the digestive system 

                 i) The available lactase can digest most or all of it 

                 ii) less undigested lactose reaches the colon 

                 iii) There is reduced fermentation by bacteria 

Lower lactose = lower symptom risk 

Hard and aged cheese undergo fermentation and whey removal, which drastically reduces lactose 

→ Fermented Dairy Foods 

Fermented dairy foods go through a process where beneficial bacteria (live cultures) break down lactose into simpler compounds such as lactic acid.

These bacteria consume a significant portion of the lactose during fermentation and produce enzymes that continue helping digest lactose in your gut

This means fermented products like yogurt and kefir often contain less lactose than milk and actively assist digestion.

Additionally, the probiotics found in fermented foods can:                  

                 +Improve gut microbiome balance

                 +Enhance lactose digestion over time

                 +Reduce gastrointestinal symptoms in some people

What to avoid

These dairy products have higher lactose content that often triggers symptoms: 

Regular cows milk 

Soft, fresh cheeses such as ricotta , cottage cheese and cream cheese- contain more lactose due to minimal aging 

Source:

Labrie, V., Buske, O. J., Oh, E., Jeremian, R., Ptak, C., Gasiūnas, G., Maleckas, A., Petereit, R., Žvirbliene, A., Adamonis, K., Kriukienė, E., Koncevičius, K., Gordevičius, J., Nair, A., Zhang, A., Ebrahimi, S., Oh, G., Šikšnys, V., Kupčinskas, L., Brudno, M., … Petronis, A. (2016). Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging. Nature structural & molecular biology, 23(6), 566–573. https://doi.org/10.1038/nsmb.3227

Bayless, T. M., Brown, E., & Paige, D. M. (2017). Lactase Non-persistence and Lactose Intolerance. Current gastroenterology reports, 19(5), 23. https://doi.org/10.1007/s11894-017-0558-9