Lactose malabsorption and intolerance: causes, tests and treatment
What it found
Most people worldwide cannot fully digest lactose after childhood, but many of them can still drink a glass of milk without symptoms.
Symptoms depend on the dose, how much lactase the gut makes, and the gut bacteria.
What they found
Studies in people
Most people cannot digest it
A recent meta-analysis estimated that 68% of people worldwide have lactose malabsorption. Rates are lowest in Nordic countries, under 5% in Denmark, and highest in Korean and Han Chinese populations, approaching 100%.
Symptoms and dose
Most people with lactose malabsorption can tolerate at least 12 g of lactose, about 250 mL of milk, without problems. Larger amounts may be tolerated if taken with food or spread over the day.
IBS and sensitivity
In a double-blinded randomised cross-over study in a South Chinese population, people with diarrhoea-predominant IBS had a much higher risk and severity of symptoms after lactose, especially at the low to moderate doses found in a normal diet.
Treatments
A low-lactose diet, lactase tablets and prebiotics can all help, but the effects are modest. In one study, after 1 month, 30% of patients taking galacto-oligosaccharides considered themselves lactose tolerant versus 6% on placebo.
Studies in people and animals
Gut bacteria and lactose
When incubated in the lab with lactose, faecal samples from lactose-intolerant subjects produced short chain fatty acids faster and in higher amounts than samples from lactose-tolerant subjects. Regular lactose intake has been linked to more Bifidobacteria and Lactobacilli in the gut.
Other findings
What lactose is
Lactose is the main sugar in milk. Cow's milk has about 5 g per 100 mL, which is 12.5 g in a typical 250 mL serving. Yoghurt has about half the lactose of unprocessed milk, and long-ripened cheese has little.
Tests for lactose problems
Genetic tests can detect the common lactase non-persistence variant in Caucasians but not secondary causes. Breath tests measure hydrogen after a lactose drink, and a rise of at least 20 ppm within 3 hours is diagnostic of lactose malabsorption.
What the authors conclude
“Most individuals with lactose malabsorption tolerate a dose of at least 12 g lactose (corresponding to 250 mL of milk) without problems.”
Also in their conclusions
- They say that primary genetic lactase persistence and non-persistence are common in healthy humans.
- They advise that a strict lactose-free diet is not required, since patients with lactose intolerance often tolerate up to 250 mL of milk without symptoms.
- They call for a well-accepted, practical and cost-effective test for food intolerance that can predict how someone will respond to dietary treatment.
How it was done
The authors wanted to bring together recent developments in how lactose is digested, how lactose malabsorption and intolerance are diagnosed, and how they are managed.
They reviewed studies on lactose digestion, the genetics of lactase, the role of gut bacteria, tests for lactose malabsorption and intolerance, and treatments including low-lactose diets, lactase supplements and prebiotics.
What it can’t tell you
- This is a review, so it cannot prove cause and effect for any single finding.
- The link between lactose and long-term health outcomes like bone density and heart health is still unclear, and studies disagree.
- It is not known whether neurological symptoms reported after lactose are actually caused by lactose malabsorption.
Who paid
- Conflicts
- Competing interests: MF has received research funding from Nestlé International for studies of lactose digestion and tolerance.
- Authors work at
- University Hospital Zürich, Switzerland; University of Leuven, Belgium; Laboratory and Clinic for motility disorders and functional GI diseases, Switzerland
The paper
- Title
- Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Misselwitz B, Butter M, Verbeke K, Fox MR (2019). Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut. doi:10.1136/gutjnl-2019-318404Free full textPubMed 31427404DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error