Lactose intolerance
Also called: lactose malabsorption, dairy intolerance, lactase deficiency
Lactose intolerance is a reduced ability to break down lactose, the sugar in dairy, because the body produces less of the enzyme lactase. Symptoms include bloating, wind, cramps and loose stools 30 minutes to 2 hours after dairy. It is not an allergy. Most people who are intolerant can still tolerate small amounts, especially in fermented or hard-cheese forms.
Why it happens
Lactase is the enzyme that splits lactose (a milk sugar) into two smaller sugars your body can absorb. Production of lactase peaks in infancy and declines for most of the world's adults. Rates vary dramatically by ancestry: under 30 percent of adults in Northern European populations have reduced lactase activity, compared with 70 percent or more in East Asian, West African and Middle Eastern populations. So the global picture depends heavily on which populations you are weighting.
What it feels like
- Bloating and a visibly distended belly within 1 to 2 hours of dairy.
- Wind that is louder, more frequent and often more odorous than usual.
- Cramping, gurgling, and the urge to go.
- Loose, watery or explosive stools, sometimes with a mucousy quality.
- Symptoms scale with dose. A latte may be fine, a milkshake may not be.
How it is tested
The hydrogen breath test is the standard. You drink a measured dose of lactose on an empty stomach, then breathe into a bag every 30 minutes for 3 hours. Hydrogen rising above a threshold confirms malabsorption. A genetic test can identify the LCT gene variant linked to lactase persistence, but it does not predict symptoms reliably and is rarely worth the cost.
How to find your tolerance
- Cut all dairy for 2 weeks. If symptoms do not improve, lactose is unlikely to be the issue.
- Reintroduce hard cheese first (cheddar, parmesan, gouda). These are nearly lactose-free.
- Then add fermented dairy: live yoghurt, kefir, aged cheese. Bacterial fermentation has already broken down most of the lactose.
- Then add small portions of fresh milk: 50 ml, 100 ml, 200 ml. Note the dose at which symptoms reappear.
- Keep below that dose, or use a lactase enzyme tablet (Lactaid, Colief) when going over.
Not the same as a milk allergy
Cow milk protein allergy is an immune response to milk protein, not the sugar. It can cause hives, swelling, breathing difficulty, or in rare cases anaphylaxis. It is most common in infants and children. If your reaction includes anything beyond gut symptoms, see a GP and request specific allergy testing.
Common questions
- Can lactose intolerance develop later in life?
- Yes. Lactase production naturally declines with age in most adults. It can also drop temporarily after gut infections, antibiotic courses, or in inflammatory bowel conditions. Sometimes the intolerance resolves once the underlying cause settles.
- Is lactose-free milk just normal milk with the lactose removed?
- Almost. Lactose-free milk has the lactase enzyme added during processing, which splits the lactose into glucose and galactose before you drink it. The taste is slightly sweeter for the same reason. Nutritional content is otherwise identical.
- Are oat, almond and soy milks lactose-free?
- Yes, all plant-based milks are naturally lactose-free. Calcium content varies. Fortified versions match dairy. Unfortified almond and rice milks are low in calcium and protein and not great staples for adults relying on them as a main source.
- Can probiotics help lactose intolerance?
- Mildly. Some probiotic strains, particularly Lactobacillus and Bifidobacterium species, produce small amounts of lactase. The effect is real but modest. Yoghurt with live cultures is often better tolerated than the equivalent dose of milk for the same reason.