Quick answer: Lactose intolerance means getting symptoms such as bloating, wind, cramps or loose stools after dairy because the gut produces too little lactase, the enzyme that digests milk sugar. Around two-thirds of adults worldwide absorb lactose poorly, yet many can still tolerate moderate amounts, especially with food. It can also appear later in life or temporarily after a gut infection, coeliac disease or SIBO. A breath test can help confirm it, and most people do not need to remove dairy completely – finding your own threshold and choosing low-lactose options is usually enough.
Dairy is one of the first things people cut when they feel bloated, and sometimes that is the right call. But I also meet many people who have removed all dairy for years without being sure it was the problem – and are now missing out on calcium, protein and foods they enjoy. If you are unsure whether you are dealing with an intolerance or an allergy, start with food intolerance vs food allergy.
What are the symptoms of lactose intolerance in adults?
Symptoms usually appear between 30 minutes and a few hours after eating or drinking dairy, and are commonly associated with:
- bloating and a distended tummy
- wind and gurgling
- cramping or abdominal discomfort
- loose stools or diarrhoea
- sometimes nausea
They happen because undigested lactose draws water into the bowel and is then fermented by gut bacteria, producing gas. The severity depends on how much lactose you have, what you eat it with, and how sensitive your gut is in general – which is why people with IBS often react more strongly.1
Can you develop lactose intolerance later in life?
Yes. In most of the world's population, lactase production naturally falls after early childhood – this is called lactase non-persistence. A global meta-analysis estimated that about 68% of adults have lactose malabsorption, with large differences between regions: rates are lower in northern Europe and higher in southern Europe, Africa and Asia.2 Because lactase declines gradually, symptoms can appear in adulthood.
There is also secondary lactose intolerance, where the lining of the small intestine is temporarily affected – after gastroenteritis, with active coeliac disease, inflammatory bowel disease or SIBO. In these cases tolerance often returns when the underlying issue settles.
Is lactose malabsorption the same as lactose intolerance?
Not quite. Malabsorption means lactose is not fully digested; intolerance means that malabsorption causes symptoms. Many people with malabsorption have few or no symptoms at normal intakes, and studies show that symptoms often correlate poorly with test results – expectation and overall gut sensitivity play a role too.1 This is why a test result should always be read alongside how you actually feel.
How is lactose intolerance tested?
- Hydrogen breath test: you drink a dose of lactose and breath samples are collected over a few hours. It is the most commonly used test.1
- Genetic test: shows whether you carry the gene variant for lactase persistence. It cannot tell you about secondary intolerance or whether you actually get symptoms.
- Structured elimination and reintroduction: removing lactose for two to four weeks and then reintroducing it in measured amounts, ideally with a food and symptom diary, is a practical way to see what you tolerate.
Because the symptoms overlap with coeliac disease, IBS and SIBO, it is worth discussing persistent symptoms with your doctor rather than assuming dairy is the only cause.
When to see your doctor first
- Blood in the stool or black stools
- Unintended weight loss, fever or diarrhoea that wakes you at night
- Iron deficiency or other signs of poor absorption
- New, persistent bowel changes after the age of 50
- A family history of coeliac disease or inflammatory bowel disease
How much lactose can you tolerate?
More than many people expect. A US National Institutes of Health consensus concluded that most adults with lactose malabsorption can tolerate around 12 g of lactose in one sitting – roughly a glass of milk – with minimal or no symptoms, especially when it is taken with food and spread across the day.3
Some dairy foods are naturally low in lactose:
- hard and aged cheeses such as Parmesan, mature Cheddar and Manchego
- butter
- natural yoghurt and kefir, where bacteria have already digested part of the lactose
- lactose-free milk and yoghurts
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- Have dairy with a meal rather than on its own.
- Keep portions moderate and spread them across the day.
- Choose low-lactose options first and test your threshold gradually.
- Lactase enzyme drops or tablets taken with dairy may help some people – they are optional and individual.
- If you reduce dairy significantly, make sure calcium, iodine and protein are covered from other foods.
Regular, gradual exposure to small amounts may improve how comfortable dairy feels for some people, probably through adaptation of the gut bacteria rather than any increase in lactase itself; the evidence is limited, so go slowly and listen to your gut.1
Frequently asked questions
Does lactose intolerance get worse with age?
It can, because lactase production naturally falls over time in most people. Symptoms can also fluctuate with gut infections, stress and other digestive conditions.
Can lactose intolerance cause bloating only?
Yes. Some people mainly notice bloating and wind without diarrhoea. Because bloating has many causes, a structured test or reintroduction helps confirm whether lactose is really the trigger.
Is lactose-free milk healthy for people with IBS?
Lactose-free milk has the same protein and calcium as regular milk, with the lactose already broken down. It is a useful option for many people with IBS who react to lactose.
Can you become lactose tolerant again?
If the intolerance is secondary to a gut infection, coeliac disease or SIBO, tolerance often improves when the underlying issue settles. Primary lactase decline is usually permanent, but many people still tolerate moderate amounts.
Is yoghurt OK if I'm lactose intolerant?
Natural yoghurt and kefir are often better tolerated than milk because their live bacteria have already digested part of the lactose. Start with small portions and see how you feel.
References
- Misselwitz B, et al. Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut. 2019. PubMed: PMID 31427404
- Storhaug CL, et al. Country, regional, and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2017. PubMed: PMID 28690131
- Suchy FJ, et al. National Institutes of Health Consensus Development Conference: lactose intolerance and health. Ann Intern Med. 2010. PubMed: PMID 20404261
This article is for educational purposes and is not medical advice. Nutritional therapy does not replace medical care. Always work with your doctor for any persistent or new symptoms and before making changes to your care, medication or supplements.