Quick answer
What is lactose intolerance?
Lactose intolerance means insufficient lactase enzyme to break down lactose (milk sugar) — causing bloating, wind, cramps, and diarrhoea after dairy products. Different from milk allergy (immune reaction). Common in adults especially of East Asian, African, and South Asian background. Managed by reducing lactose, using lactose-free milk, or lactase enzyme tablets — not always needing complete dairy avoidance. Ensure adequate calcium from other sources if dairy limited.
Lactose intolerance — milk sugar malabsorption
Lactose is disaccharide sugar in milk and dairy — requires lactase enzyme in small intestine to split into glucose + galactose for absorption.
Lactase non-persistence — genetically programmed decline after weaning — normal for most humans globally — ~65% world population.
Northern Europeans — lactase persistence mutation — dairy tolerance common.
Symptoms
After lactose load (dose-dependent):
- bloating, flatulence
- abdominal cramps
- borborygmi (rumbling)
- loose stool/diarrhoea
Timing: 30 min – 2 hours — intestinal fermentation by bacteria
NOT:
- immediate urticaria — allergy
- weight loss, blood in stool — investigate other causes
Lactose intolerance vs milk allergy
| Lactose intolerance | Milk allergy | |
|---|---|---|
| Mechanism | Enzyme deficiency | IgE/non-IgE immune |
| Onset | Delayed | Minutes–hours |
| Anaphylaxis | No | Possible |
| Age | Teens/adults common | Infants common |
Milk allergy — separate condition — paediatric/allergy clinic.
Diagnosis
- Clinical history — relationship to dairy dose
- 2–4 week low lactose trial — symptoms improve
- Lactose challenge — symptoms return
- Hydrogen breath test — specialist
- Exclude coeliac — IgA TTG — see coeliac disease
Management
Reduce lactose dose
- trial tolerance level — may tolerate milk in tea not pint of milk
Lactose-free products
- Lactose-free milk — same calcium
- plant milks — check calcium fortified
Lactase supplements
- tablets with dairy meal
Usually tolerated
- hard cheese
- butter — minimal lactose
- probiotic yoghurt — individual trial
Nutrition if dairy limited
Calcium targets:
- 700mg/day adults — 1000mg pregnancy
Sources:
- fortified plant milk
- tinned fish with bones
- green leafy veg
- fortified bread
- supplements if inadequate
Vitamin D — see NHS guidance
Secondary lactose intolerance
Temporary after:
- gastroenteritis
- coeliac (until treated)
- IBD flare
Lactase returns when gut heals — retrial dairy later.
When to see GP
Red flags NOT lactose alone:
- nocturnal diarrhoea
- weight loss
- rectal bleeding
- anaemia
→ IBD, coeliac, cancer screen as indicated.
Lactose intolerance is annoying not dangerous — diagnosis prevents unnecessary dairy fear and ** ensures calcium** if intake drops.
Common questions
- What are the symptoms of lactose intolerance?
- Bloating, excessive wind, abdominal cramps, gurgling, diarrhoea or loose stools — typically 30 minutes to 2 hours after milk, ice cream, soft cheese, or large dairy portions. Severity depends on lactose dose and your enzyme level — small amounts in tea may be fine.
- What is the difference between lactose intolerance and milk allergy?
- Lactose intolerance — digestive enzyme deficiency — not immune — never causes anaphylaxis. Milk allergy — immune reaction to milk protein — can cause urticaria, vomiting, wheeze, anaphylaxis within minutes to 2 hours — more common in infants. Different tests and treatments.
- Can I still eat cheese if lactose intolerant?
- Often yes — aged hard cheeses (cheddar, parmesan) contain minimal lactose. Yoghurt with live cultures may be tolerated — bacteria partially digest lactose. Fresh milk, ice cream, and soft cheeses highest lactose — most problematic.
- How is lactose intolerance diagnosed?
- Clinical history often sufficient — trial off lactose then challenge. Hydrogen breath test after lactose drink — rises if malabsorption. Coeliac screen if symptoms overlap — untreated coeliac causes secondary lactose intolerance improving on gluten-free diet.
- Do lactase enzyme tablets work?
- Lactase supplements (Lactaid etc.) taken with dairy help many people digest lactose — effectiveness varies. Lactose-free milk has enzyme added — tastes slightly sweeter — good calcium source.