Food and the gut
Why milk causes bloating: understanding lactose intolerance in India
Lactose intolerance means that the body does not make enough lactase, the enzyme that digests the sugar in milk. Undigested lactose reaches the colon, where bacteria ferment it, causing gas, bloating, cramps and loose stools within a few hours of drinking milk. It is common in Indian adults and is managed by adjusting the amount and type of dairy, not by avoiding it completely.
In short
- About two-thirds of the world’s adults digest lactose poorly. It is the usual state for adult humans, not a disease.
- Symptoms depend on the dose. Most people tolerate small amounts.
- Curd, buttermilk, paneer and ghee are usually fine.
- A two-week trial, or a hydrogen breath test, confirms it.
What happens in lactose intolerance?
Lactose is a sugar made of two smaller sugars joined together. Lactase, an enzyme on the lining of the small intestine, splits them so that they can be absorbed. Babies have plenty of lactase. In most people it declines after early childhood.
When lactose is not split, it stays in the gut, draws in water and passes to the colon. Bacteria there ferment it into gas and acids.
What are the symptoms?
Thirty minutes to two hours after milk or milk-based foods:
- Bloating and a feeling of fullness
- Rumbling and excess gas
- Cramping in the lower abdomen
- Loose stools
- Sometimes nausea
The severity depends on how much lactose was taken, what it was eaten with, and how sensitive the gut is.
Why is it common in India?
The ability to digest lactose through adult life is a genetic trait that became common in populations with a long history of drinking fresh milk. Across India it varies by region and community, and a large share of adults have reduced lactase. Traditional Indian diets reflect this: much of the dairy is taken as curd, buttermilk, paneer and ghee, which contain little lactose.
Can it develop suddenly?
Yes. A gut infection, coeliac disease or another condition that injures the lining of the small intestine removes the lactase-producing cells for a time. This is called secondary lactose intolerance, and it improves as the lining heals. New intolerance in an adult, especially with weight loss or anaemia, is a reason to look for an underlying cause.
How is it confirmed?
A home trial
Stop milk and milk products for two weeks. If symptoms settle and then return when a glass of milk is reintroduced, the diagnosis is likely.
A hydrogen breath test
You drink a measured amount of lactose, and breath samples are taken over two to three hours. A rise in hydrogen together with symptoms confirms that lactose is not being absorbed. See breath tests.
How is it managed?
Find your threshold
Most people with lactose intolerance can take about one cup of milk a day, especially in divided amounts with meals.
Choose low-lactose dairy
Curd, buttermilk, paneer, hard cheese and ghee.
Use lactose-free milk
It is ordinary milk in which the lactose has already been split. The nutrients are the same.
Lactase tablets
Taken with a dairy-containing meal, they supply the missing enzyme. Useful when eating out.
Protect your nutrition
Keep up calcium, protein and vitamin B12 from other dairy or from alternatives.
Is it the same as milk allergy?
No. Milk allergy is an immune reaction to milk protein. It causes hives, swelling, wheezing or vomiting, can be severe, and requires complete avoidance. Lactose intolerance is a digestive problem and is never dangerous.
When should I see a doctor?
See a doctor if symptoms continue after removing lactose, or if you have weight loss, blood in the stool, fever, night-time diarrhoea or anaemia. Bloating has many other causes. See bloating.
Questions patients ask me
Do I have to give up tea and coffee with milk?
Usually not. The small amount of milk in a cup of tea is tolerated by most people. Several large, milky cups a day may add up.
Will my tolerance improve if I keep drinking milk?
The enzyme does not return, but regular small amounts allow gut bacteria to adapt, and symptoms often lessen.
Can lactose intolerance cause weight loss?
No. If you are losing weight, another cause must be looked for.
Are there hidden sources of lactose?
Yes: some breads, biscuits, sauces, protein powders and tablets contain milk solids or lactose. The amounts are usually too small to matter unless you are very sensitive.
Sources
This page is written for patients and is based on the guidelines and studies below. It is for education and does not replace a consultation.
- Review of lactose malabsorption and intolerance. Misselwitz B et al. Gut. 2019. PubMed 31427404
- North American consensus on hydrogen and methane breath testing. Rezaie A et al. Am J Gastroenterol. 2017. PubMed 28323273
- American College of Gastroenterology guideline on irritable bowel syndrome. Lacy BE et al. Am J Gastroenterol. 2021. doi:10.14309/ajg.0000000000001036