Patient information · Gastroenterology
Lactose intolerance
and why most people can keep some dairy
Lactose intolerance is difficulty digesting the sugar in milk, causing bloating, wind and diarrhoea. It is not an allergy, it is not dangerous, and it is the normal adult state for most of the world's population. Most people with it can still tolerate a useful amount of dairy, which matters for calcium.
Seek assessment rather than assuming lactose intolerance if there is
- blood or mucus in the stool
- unexplained weight loss, or symptoms waking you at night
- severe abdominal pain, or vomiting
- swelling of the lips or face, hives, or wheeze after dairy — this is allergy, not intolerance
- anaemia, or symptoms starting suddenly in an adult
- faltering growth in a child
Blood, weight loss and night symptoms point to inflammatory bowel disease or coeliac disease, not intolerance. Any immediate reaction with swelling, hives or breathing difficulty after dairy is an allergy and needs proper allergy assessment — the two are entirely different.
Intolerance or allergy?
- Lactose intolerance — a digestive problem. The enzyme lactase is reduced, so lactose ferments in the colon producing gas. Symptoms come on 30 minutes to a few hours after dairy: bloating, wind, cramps, rumbling and loose stools. Dose-dependent — a splash of milk in tea is usually fine, a large latte is not.
- Cow's milk allergy — an immune reaction to milk protein. Can cause hives, swelling, wheeze and anaphylaxis, and is far more common in infants than adults. Even tiny amounts matter.
- Confusing the two leads to unnecessary avoidance on one hand and dangerous exposure on the other.
It is the global norm
Around 65 to 70% of the world's adults have reduced lactase — over 90% in East Asian populations and high proportions in African, South Asian, Middle Eastern and Southern European ancestry. Persistent lactase into adulthood is the genetic exception, most common in Northern Europeans. So this is not a disease or a deficiency; it is the ancestral human default. It typically develops gradually from late childhood onwards rather than appearing suddenly.
Secondary lactose intolerance
Lactase lives on the tips of the intestinal lining, so anything damaging that lining causes temporary intolerance — gastroenteritis, coeliac disease, Crohn's disease, or a course of antibiotics. This usually recovers over weeks to months once the underlying problem settles. If intolerance appears suddenly in an adult, it is worth looking for a cause rather than simply cutting out dairy — coeliac disease in particular presents this way.
Confirming it
- Often diagnosed by a trial of exclusion for two weeks followed by reintroduction — simple, free, and usually conclusive.
- A hydrogen breath test confirms it objectively where the picture is unclear.
- Coeliac screening should be done first, while you are still eating gluten, since it commonly presents identically.
- Keeping a food and symptom diary for two weeks is more useful than any commercial intolerance test.
- IgG food intolerance tests sold online have no scientific validity and routinely produce long lists of foods to avoid, which does harm.
How much you can have
Usually well tolerated
- Hard cheeses — cheddar, parmesan — contain almost no lactose
- Live yoghurt and kefir; the bacteria digest the lactose for you
- Butter, which is nearly all fat
- Small amounts spread through the day rather than at once
- Dairy taken with a meal rather than alone
More likely to cause symptoms
- Large glasses of milk, milkshakes and large lattes
- Soft cheeses, cream and ice cream in quantity
- Milk on an empty stomach
- Hidden lactose in sauces, soups, processed foods and some medicines
- Whey protein powders
Most people with lactose intolerance tolerate around 12g of lactose — roughly a glass of milk — in a day if it is spread out. Lactase enzyme tablets taken with dairy work well and allow occasional flexibility.
Calcium
This is the reason not to cut dairy out entirely without need. Adults need around 700mg of calcium a day, more in some circumstances. Good non-dairy sources include fortified plant milks (choose fortified ones — organic versions often are not), tinned fish with bones, tofu set with calcium, leafy greens such as kale and pak choi, almonds and fortified breads. Vitamin D matters alongside for absorption.
Why come to us. Cutting out dairy without a diagnosis risks missing coeliac disease, inflammatory bowel disease or something else that presents identically — and risks your bone health for no reason. We take coeliac screening, full blood count, ferritin, calcium and vitamin D in-house with results explained in the same visit, arrange breath testing and dietitian input through our CQC-registered partners, and help you work out how much dairy you can actually keep. Seven days a week, no referral needed.
Coeliac excluded before you cut out dairy
Bloods in-house, results the same visit. Seven days a week.
Tower Bridge Hospital London
97–99 Whitechapel Road, London E1 1DT
WhatsApp 07903 284 189
info@mhwclinic.co.uk
Open Mon–Sat, 9am–7pm (closed Sundays until September)
In an emergency
Call 999, or go to the Royal London Hospital Emergency Department, Whitechapel Road, London E1 1FR.
When we are closed and it is not an emergency
Call NHS 111 or visit 111.nhs.uk.