Lactose Intolerance: What You Need to Know
If you've ever experienced bloating, gas or abdominal discomfort after drinking milk or eating dairy, you may have wondered whether lactose intolerance could be the culprit.
But lactose intolerance doesn't necessarily mean you need to say goodbye to dairy altogether.
Understanding how lactose is digested, how much you can tolerate, and which dairy foods are naturally lower in lactose can help you manage symptoms while still enjoying a varied and nutritionally adequate diet.
What is lactose intolerance?
Lactose is the natural sugar found in milk and many dairy products.
To digest lactose, our small intestine produces an enzyme called lactase. Lactase breaks lactose down into two smaller sugars — glucose and galactose — which can then be absorbed into the bloodstream.
When the body doesn't produce enough lactase, lactose isn't completely digested in the small intestine. Instead, it travels into the large intestine, where it is fermented by gut bacteria.
This fermentation can produce gas and draw water into the bowel, contributing to symptoms such as:
→ bloating
→ abdominal pain or cramping
→ excessive gas
→ tummy rumbling or gurgling
→ diarrhoea
→ sometimes nausea
Symptoms can depend on several factors, including:
The amount of lactose consumed: A larger dose is more likely to cause symptoms.
Your individual tolerance: Lactose tolerance varies significantly from person to person.
The food it's consumed in: Some dairy foods are naturally lower in lactose than others.
What else you're eating: Consuming lactose as part of a meal may be better tolerated than consuming a large amount on its own.
It's worth remembering that these symptoms aren't specific to lactose intolerance. Other gastrointestinal conditions can cause very similar symptoms, so experiencing bloating after dairy doesn't automatically mean you have lactose intolerance.
Importantly, lactose intolerance isn't necessarily an "all or nothing" situation.
The amount of lactose someone can tolerate varies considerably between individuals. Some people may experience symptoms after a large glass of milk but tolerate a small amount in coffee, yoghurt or cheese without any issues.
It's also important to distinguish lactose intolerance from cow's milk allergy.
Lactose intolerance relates to difficulty digesting lactose (the sugar) in milk. Cow's milk allergy involves an immune response to proteins found in milk and is a different condition requiring different management.
What causes lactose intolerance?
Lactose intolerance occurs when the small intestine doesn't produce enough of the enzyme lactase to properly digest lactose.
But there isn't just one reason this can happen.
Primary lactose intolerance
For most people, lactase production naturally decreases after weaning and into adulthood. This is sometimes referred to as primary lactase deficiency.
How much lactase someone continues to produce varies between individuals, which is one reason lactose tolerance can differ so much from person to person.
Some people continue to produce enough lactase to tolerate relatively large amounts of lactose, while others produce less and may experience symptoms after smaller amounts.
Secondary lactose intolerance
Lactose intolerance can also develop temporarily when the small intestine is damaged or inflamed.
For example, gastroenteritis or other infections can temporarily damage the cells lining the small intestine and reduce lactase activity. Other conditions affecting the small intestine, such as coeliac disease or inflammatory bowel disease, can also contribute.
This can mean someone who previously tolerated dairy suddenly develops symptoms after eating lactose-containing foods.
The good news is that secondary lactose intolerance can improve when the underlying cause is treated and the gut lining heals.
In these situations, temporarily reducing lactose may help while the gut recovers, followed by gradual reintroduction as tolerated.
So if you've recently had gastroenteritis and suddenly find that milk is upsetting your stomach, it doesn't necessarily mean you've developed permanent lactose intolerance.
Congenital lactase deficiency
Very rarely, babies are born with an inability to produce lactase. This is known as congenital lactase deficiency and is different from the more common forms of lactose intolerance that develop later in life.
For most people, lactose intolerance develops later in life or occurs temporarily following damage to the small intestine.
Is lactose important for gut health?
This is where things get interesting.
When lactose isn't fully digested and reaches the large intestine, it is fermented by our gut bacteria. This produces various metabolites, including short-chain fatty acids.
Research has also investigated how lactose consumption can influence the gut microbiota, including bacteria such as Bifidobacterium, particularly in infancy.
However, this doesn't mean that someone with lactose intolerance needs to consume enough lactose to trigger symptoms in the name of "gut health".
For adults, the goal is generally to find the amount of lactose you can comfortably tolerate rather than avoiding lactose unnecessarily — or deliberately consuming large amounts of it.
If lactose causes significant symptoms, there is no reason to force yourself to eat it.
Where is lactose found?
Lactose is found naturally in milk and dairy products, but the amount can vary considerably between foods.
Foods Higher in Lactose include:
cow's milk
goat’s milk
condensed milk
evaporated milk
ice cream
yoghurts
custards
milk-based desserts
some fresh or soft cheeses
Naturally lower-lactose options include:
hard or mature cheeses
butter
lactose-free milk
lactose-free yoghurt
some yoghurts, depending on the product and your individual tolerance
Fermentation and processing can reduce the amount of lactose in some dairy foods, which is one reason yoghurt and mature cheeses may be better tolerated than milk by some people.
This is one reason why "I can't tolerate dairy" isn't always an accurate description. Lactose-free dairy is still dairy. Lactose-free milk and other lactose-free dairy products have had the lactose broken down into simpler sugars, but they can still provide many of the same nutrients found in regular dairy.
So if lactose is the problem, you may be able to continue enjoying dairy by choosing lactose-free alternatives rather than removing dairy altogether.
Do I need to avoid dairy?
For many people with lactose intolerance, completely eliminating dairy isn't required.
Instead, there are several strategies that may help you find your individual tolerance:
Reduce the portion size: You may tolerate a small amount of lactose but experience symptoms after a larger amount.
Spread lactose throughout the day: Rather than consuming a large amount of lactose in one sitting, smaller amounts across the day may be better tolerated.
Have lactose-containing foods with a meal: Some people find lactose easier to tolerate when consumed as part of a meal rather than on its own.
Choose naturally lower-lactose dairy: Hard cheeses and butter contain very little lactose, while yoghurt may be tolerated better than milk by some people.
Choose lactose-free dairy: Lactose-free milk, yoghurt and other dairy products can be an easy way to continue eating dairy without the same lactose load.
Consider lactase enzyme supplements: Lactase enzyme supplements can help some people digest lactose, particularly when eating away from home or when you want to enjoy a food that contains more lactose.
The right approach will depend on your individual symptoms, dietary preferences and nutritional needs.
Don't forget about calcium
One of the biggest concerns with unnecessarily eliminating dairy is missing out on important nutrients — particularly calcium.
Most adults need 2-3 serves of dairy/dairy alternatives per day. This may be different depending on your age, gender or life stage.
Dairy foods can provide:
calcium
protein
iodine
vitamin B12
riboflavin
phosphorus
vitamin D in fortified products
Lactose-free dairy products can provide many of the same nutritional benefits as their regular counterparts.
If dairy isn't part of your diet, there are also plenty of other ways to meet your calcium needs.
High-calcium dairy alternative foods include:
calcium-fortified soy milk and other calcium-fortified plant milks
calcium-set tofu
canned fish with edible bones, such as sardines and salmon
tahini and sesame seeds
almonds
bok choy and other calcium-containing vegetables
legumes
other calcium-fortified foods
When choosing a plant-based milk as a replacement for cow's milk, check the nutrition panel for calcium fortification.
Calcium-fortified soy milk is also one of the plant-based options that is nutritionally similar to cow's milk in several important ways, including its protein content.
Can probiotics help?
You may have heard that probiotics can help with lactose intolerance.
The evidence is promising, but it's important not to lump all probiotics together.
Research suggests that some specific probiotic strains may improve lactose digestion and/or reduce symptoms, but probiotic effects are strain-specific.
In other words, the fact that one probiotic strain has been studied doesn't mean every probiotic supplement will have the same effect.
Research has investigated strains from groups including:
Lactobacillus
Bifidobacterium
Saccharomyces
There has also been research into the DDS-1 strain of Lactobacillus acidophilus, with some studies finding improvements in symptoms of lactose intolerance.
A 2023 meta-analysis examining probiotics and lactose intolerance in adults found evidence of improvements in some measures of lactose intolerance, although the findings varied between studies and more research is needed to determine which strains, doses and formulations are most useful.
So rather than thinking "probiotics cure lactose intolerance", it's more accurate to say that certain probiotic strains may help some people manage their symptoms.
Can I improve my tolerance to lactose?
This is one of the most important things to know about lactose intolerance.
You may not need to avoid lactose forever.
If you've been avoiding dairy completely, it can be tempting to assume that every amount of lactose will cause symptoms. But many people with lactose intolerance can tolerate at least some lactose, particularly in smaller amounts.
Once symptoms are well controlled, gradually reintroducing lactose can help you work out your individual tolerance.
This might mean starting with a small amount of a lower-lactose food and gradually increasing the amount as tolerated.
For example:
small amount → assess symptoms → gradually increase if comfortable → find your personal tolerance
This isn't about forcing yourself to eat foods that make you feel unwell.
It's about finding the maximum amount you can comfortably tolerate, rather than automatically restricting more foods than necessary.
And if your lactose intolerance is secondary to something like gastroenteritis, your tolerance may improve naturally as your gut recovers.
Because everyone's tolerance is different, there isn't one universal "safe amount" of lactose for everyone.
The takeaway
Lactose intolerance doesn't have to mean giving up dairy.
For many people, managing lactose intolerance is less about "what foods can I never eat again?" and more about "how much can I tolerate, and what strategies help me enjoy these foods comfortably?"
You may be able to tolerate more lactose than you think — particularly when you adjust portion sizes and spread lactose throughout the day.
And if you've been avoiding dairy for a while, working with a dietitian can help you safely assess your tolerance, support adequate calcium and nutrient intake, and gradually expand your food choices where appropriate.