Lactose digestion, intolerance symptoms and how they are managed
What it found
Most people worldwide lose the ability to fully digest lactose after childhood, but many can still handle a glass of milk without stomach trouble.
Symptoms like bloating and pain depend on the amount eaten, gut bacteria and conditions like irritable bowel syndrome.
What they found
Studies in people
How much lactose is tolerated
Most people who struggle to digest lactose can handle at least 12 g, which is about one 250 mL glass of milk, without stomach problems. Eating it with other foods or spreading it through the day helps people tolerate more.
Irritable bowel makes symptoms worse
People with irritable bowel syndrome are much more likely to feel pain and bloating after eating lactose, even at normal dietary amounts. Anxiety and a sensitive gut lining also make these stomach symptoms stronger.
Prebiotics may ease symptoms
In a trial of 85 people with lactose intolerance, taking a prebiotic supplement for one month changed their gut bacteria. After treatment, 30% of those taking the prebiotic felt they could handle lactose, compared with 6% taking a dummy pill.
Studies in people and animals
Gut bacteria adapt to dairy
Regularly eating lactose changes gut bacteria in ways that may reduce gas and stomach symptoms over time. Lab tests and studies in people show increases in helpful bacteria like Bifidobacteria when lactose is consumed regularly.
Other findings
Lactose is hidden in foods
Cow's milk has about 5 g of lactose per 100 mL. Yoghurt has roughly half the lactose of plain milk, while aged cheese has very little. Lactose powder is also added to processed foods like sausages, bread, sauces and margarines to improve texture and flavour.
What the authors conclude
- They note that losing the ability to digest lactose after infancy is a normal part of human biology rather than a disease.
- They advise that most people with lactose malabsorption do not need to cut out dairy completely and can often manage small amounts.
- They call for better, practical tests that can predict whether changing the diet will actually relieve a patient's stomach symptoms.
How it was done
Scientists have long studied how people digest milk sugar because it offers clues about human evolution, diet and gut health. The authors wanted to gather recent findings on why some people get stomach symptoms from dairy and how best to test for and manage this.
The authors gathered and examined published research on how the body breaks down lactose, why some people cannot digest it and what treatments help. They looked at genetic studies, clinical trials in people and lab tests on gut bacteria.
What it can’t tell you
- This work gathers past research, so it cannot prove on its own that any single treatment causes symptom relief.
- Self-reported food intolerance does not always match up with medical test results, making it hard to know exactly who truly reacts to lactose.
- Long-term effects of avoiding dairy are difficult to measure because diets contain many different nutrients that change together.
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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error