FAQsAllergy / Intolerance

Lactose is a sugar that occurs naturally in milk and gives it its slightly sweet taste. To digest milk and other dairy products, the body relies on an enzyme called lactase. This breaks down the lactose into glucose, the basic compound that gives us energy.

Not everyone is able to produce enough lactase to do this job properly. If your body can’t fully digest lactose, you’re said to be wholly or partially lactose intolerant. Lactose that can’t be broken down by the body passes into the large intestine. Here it is processed by gut bacteria, resulting in a large amount of gas.

Milk contains a natural sugar called lactose. During digestion this is converted into glucose, our basic energy source. To break down the lactose, the body needs sufficient quantities of the enzyme lactase. If your body doesn’t produce enough lactase, it can’t fully digest lactose. This is what’s known as lactose intolerance.

Typical signs of lactose intolerance are uncomfortable bloating and wind. If not enough lactase is produced, the lactose instead passes into the large intestine for processing by gut bacteria. This creates a large amount of gas. People with a greater intolerance may experience more severe symptoms, like diarrhoea, nausea and stomach cramps.

Following a lactose intolerant diet means reducing or completely cutting out foods that contain lactose. Some sufferers must stick to an entirely lactose free diet. Others with lactose intolerance can consume small amounts of lactose without experiencing symptoms. Finding out your level of tolerance is generally down to trial and error.

Lactose is only found in milk and dairy products – and other foods containing them – so it’s fairly easy to avoid. Cow’s, goat’s and sheep’s milk all contain lactose. And there’s just as much lactose in a carton whether it’s a skimmed, semi-skimmed or full fat variety.

The good news is there are plenty of dairy free alternatives to enjoy. Next time you’re shopping, look for milk made from rice, oats, almonds, spelt or soya. Plant based milks are naturally lactose free. Many varieties are fortified with calcium and vitamins. So you get all the nutrition of a glass of milk without suffering any of the side effects.

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Lactose intolerance is caused by a shortage of lactase, the enzyme that breaks down lactose. Lactose is the naturally occurring sugar found in milk and dairy products. Without enough of this enzyme, the body can’t fully digest these foodstuffs.

Lactase is a ‘use-it-or-lose-it’ enzyme: the body makes it only if lactose is consumed regularly. So lactase production drops sharply after weaning in places where milk isn’t historically a staple of the adult diet – Africa and Asia, for example.

Why does lactose intolerance arise?

Lactose intolerance can be inherited: how much lactase a person produces can be down to genes. The condition is also associated with irritable bowel syndrome (IBS), Crohn’s disease and coeliac disease, which can sometimes make it difficult to diagnose.

People undergoing certain kinds of chemotherapy or taking an extended course of antibiotics may become lactose intolerant. A bout of a gastrointestinal infection, such as gastroenteritis or gastric flu, can damage the small intestine and bring on ‘secondary lactose intolerance’.

In the UK and other parts of Europe, lactose intolerance is thought to affect 5–15% of the adult population. Among certain ethnic groups, in particular people of Afro-Caribbean and Asian origin, this figure rises steeply. Looking at the condition on a global scale, it’s likely that two thirds of the world’s population are lactose intolerant.

There’s no clear evidence to suggest that lactose intolerance is becoming more widespread. What has increased is our awareness of the condition. Combined with more effective detection methods, this has led to more people being diagnosed as lactose intolerant and deciding to avoid lactose.

Able to tolerate some lactose? Then try taking on board these tips:

• Consuming foods that contain lactose as part of a meal, or with foods that slow the emptying of the stomach – high fibre foods, high fat foods or low glycaemic index foods – improves tolerance
• Milk may be better tolerated when drunk cold rather than warm
• Chocolate milk may be better tolerated than regular milk

If on the other hand you’re very sensitive to lactose, look out for it hiding in processed foods. Crisps, biscuits and breakfast cereals are a few foodstuffs that you might not expect to contain milk. Always check the label carefully to be certain whether or not lactose is present. If any of the following are listed, the product contains lactose:

• Milk
• Lactose
• Whey
• Curds
• Milk by-products
• Dry milk solids
• Non-fat dry milk powder

Lactose is also used in some prescription and over-the-counter medicines. Check with the pharmacist when purchasing any medicines, but especially products used to treat stomach acid and wind. These often contain lactose.

If you’re lactose intolerant, remember that skimmed and semi-skimmed milk contain just as much lactose as full fat milk. And it’s found in goat’s and sheep’s milk as well as cow’s milk. Plant based milks, however, are naturally lactose free. So choosing milk made from rice, oats, almonds, spelt or soya is a simple way to continue enjoying the great taste of milk minus the lactose.

Different dairy products contain varying amounts of lactose. Even if you can’t tolerate milk, you may be able to enjoy yogurt or cheese. Hard cheeses like Cheddar and Parmesan, for instance, are fairly low in lactose.

One of two simple tests can be used to confirm lactose tolerance. Both the hydrogen breath test and stool acidity test measure the effective digestion of lactose.

The hydrogen breath test will detect a high level of the gas in someone who is lactose intolerant. This is because hydrogen is one of the gases produced when gut bacteria in the large intestine process leftover lactose. The hydrogen is then absorbed into the bloodstream and eventually exhaled from the lungs.

It’s a simple, non-invasive test. Patients are asked to fast overnight, then given lactose dissolved in water. Breath samples are taken every 15 or 30 minutes for two hours. For an accurate result, it’s important to avoid smoking and certain foods and medicines before a hydrogen breath test.

The stool acidity test is another straightforward test of lactose intolerance. It’s generally used in the diagnosis of infants and young children. Because undigested lactose creates lactic acid and other fatty acids, testing these levels in a stool sample can detect the condition.

A person may be wholly or partially lactose intolerant. It can be a temporary or permanent condition, and it may develop at any stage in life. Symptoms generally occur between 30 minutes and 2 hours after consuming milk or another dairy product. Nevertheless, it’s often tricky for sufferers to pinpoint lactose as the culprit.

If you have low lactase levels, you may be able to tolerate around 50ml to 100ml of milk at a time, free of discomfort. So when symptoms do arise, dairy may not spring to mind as the trigger. Keeping a diary of your food intake and symptoms is the best way to spot patterns that suggest lactose intolerance.

If you have lactose intolerance, you’re far from alone. Two thirds of the world’s population are thought to be unable to digest large quantities of dairy products. Lactase is a ‘use-it-or-lose-it’ enzyme: it’s produced only if it’s needed. Where milk isn’t traditionally a staple of the adult diet – Africa and Asia, for instance – lactase production drops sharply after weaning.

Genes can also play a part in determining how much lactase a person produces, so lactose intolerance can be an inherited condition. It’s associated too with irritable bowel syndrome, Crohn’s disease and coeliac disease. Chemotherapy or an extended course of antibiotics can cause lactose intolerance. Others may experience ‘secondary lactose intolerance’, brought on by damage to the small intestine. This can be caused by a gastrointestinal infection like gastric flu.

No. Lactose free and dairy free diets are two very different things.

Lactose is only found in milk and dairy products. So a dairy free diet is automatically lactose free. But since even the lactose intolerant can generally manage to process some lactose, their diet isn’t always wholly dairy free. 

A lactose free – or low lactose – diet is followed by people who are lactose intolerant. Here the body produces too little lactase, the enzyme that breaks down lactose. The result is that lactose can’t be fully digested. Instead it passes into the large intestine for processing by gut bacteria. This activity generates a large amount of gas. 

Lactose intolerance is what’s known as a food sensitivity, rather than an allergy. Symptoms are typically mild to moderate, ranging from uncomfortable bloating and wind to diarrhoea, nausea and stomach cramps. These will come on around 30 minutes to two hours after eating lactose.

Small amounts of lactose can generally be tolerated without discomfort, unless the sufferer is highly sensitive to lactose. So a low lactose diet may still include yoghurt and cheese, and even a small amount of milk. Individuals work out how much lactose they can consume comfortably by trial and error. 

Like peanuts and shellfish, milk and dairy products can trigger an allergic reaction. A dairy free diet is essential for those who suffer from an allergy to milk protein (usually casein). In those who are allergic, the immune system typically responds immediately to any milk protein consumed. And often only a small amount is needed to cause an acute reaction.

Symptoms can be severe in milk allergy sufferers. Hives, stomach pain and vomiting are standard. In some cases, anaphylactic shock – a life threatening allergic reaction – can result. So it’s vital that all who are allergic to milk protein cut out dairy products entirely.

Milk derived ingredients are very common in processed foods. Bread, biscuits, cakes, processed meats, margarines, soups and other products that you wouldn’t think contained milk often do. Always check the label if you’re allergic, to be sure that you avoid any traces of milk protein in your diet.

Rice is one of the least allergenic foods around. So a non-dairy milk made from rice can be a great alternative source of calcium and goodness for those with a milk protein allergy. It’s tasty too. Rice milk is also lactose free. So even those who are very sensitive to lactose can drink as much of it as they like.