Milk and other dairy products contain a sugar or carbohydrate called lactose. Normally, the body breaks down lactose into its simpler components with the help of the enzyme lactase. Most mammals stop producing lactase when they are weaned. Humans, however, continue to produce it throughout life. Without enough lactase, a person can have digestive problems like abdominal pain and diarrhoea when they consume foods containing lactose. This is known as lactose intolerance or lactase deficiency.
It is rare for Caucasians to develop lactose intolerance. However, it is quite common among people from Asia, Africa, the Middle East and some Mediterranean countries, as well as among Aboriginal Australians. Up to five per cent of Caucasians and up to 75 per cent of non-Caucasians living in Australia are lactose intolerant.
Many Australian babies are unnecessarily weaned because their irritability is wrongly assumed to be lactose intolerance. In reality, the severe form of this condition – known as primary lactose intolerance (where the infant does not produce lactase from birth) – is rare.
Secondary lactose intolerance (which develops after weaning) is more common. This can occur temporarily after a bout of gastroenteritis, for example, but often improves after several weeks as the lining of the gut heals.
Symptoms of lactose intolerance
Symptoms of lactose intolerance include:
- abdominal pain
- abdominal swelling (bloating)
- flatulence (excessive wind)
If you are experiencing these symptoms and you are concerned, talk to your doctor.
It is important not to eliminate dairy foods completely from your diet if lactose intolerance is suspected, as dairy foods are rich sources of nutrients. Some dairy products (such as hard and mature cheeses) contain no lactose, and others (such as cream, butter, cottage cheese and ricotta) contain very little. Many people with lactose intolerance can tolerate small amounts of lactose with minimal symptoms.
Undigested milk sugars
The enzyme lactase breaks down milk sugar (lactose). Lactase enzymes are found in the lining of the small intestine. They change the milk sugar into absorbable compounds – glucose and galactose.
If there is not enough lactase, it skips the usual digestive process and is partially broken down by the bacteria in the intestines instead. This fermentation process causes excessive wind, bloating and associated pain. Any undigested lactose is sent along the intestinal tract. Water is not removed from the faecal matter (poo) and diarrhoea is the result.
Causes of lactose intolerance
Lactose intolerance is largely genetically determined – where your genetic make-up causes you to have less lactase than usual. Some other causes include:
- gastroenteritis – this can strip the intestines of lactase for a few weeks
- parasitic infection – this can temporarily reduce lactase levels
- iron deficiency – lack of iron in the diet can interfere with lactose digestion and absorption.
Lactose intolerance in babies
Around two thirds of babies, either breast- or bottle-fed, will experience some degree of lactase deficiency in their early months without it causing them harm. Human breastmilk contains around seven per cent lactose. The amount of lactose in breastmilk is not affected by the mother’s diet. This means the mother can’t influence the amount of lactose in her milk by reducing or eliminating dairy foods.
A bout of gastroenteritis can strip the baby’s small intestine of lactase enzymes, and lactose-free formula may need to be used for a number of weeks until the enzyme levels recover. Lactase drops available from pharmacies are another option, but these are not always helpful.
A few babies are born without any lactase enzymes at all, and lactose-free formulas may be an option in such cases. Lactose intolerance does not cause vomiting in babies. This may be symptomatic of an allergy to cows’ milk protein and should be assessed by a doctor.
Diagnosis of lactose intolerance
Various methods may be used to diagnose lactose intolerance, including:
- hydrogen breath test – this tests the amount of hydrogen that is breathed out. When lactose is fermented by bacteria in the bowel, instead of being converted by lactase, more hydrogen is produced
- elimination diet – this involves removing foods that contain lactose to see if the symptoms improve. If the symptoms reappear once the foods are reintroduced, then lactose intolerance is most likely the cause.
Another cheap and simple ‘test’ is to compare whether the person can tolerate lactose-free milk rather than ordinary milk.
Management of lactose intolerance
Most people with lactose intolerance can handle small amounts of lactose, such as a glass of milk, which contains 8–10 grams of lactose.
Some helpful tips include:
- Don’t give up milk products entirely. They are an important source of nutrients, especially calcium.
- Hard and matured cheeses such as cheddar, Edam, Swiss, mozzarella, brie and fetta contain no lactose and are tolerated by people with lactose intolerance.
- Similarly, butter and cream contain very low levels of lactose and are well tolerated.
- Yoghurt is usually well tolerated because the lactose content decreases each day as the bacteria use lactose for energy.
- Fresh cheeses such as cottage cheese and ricotta have very low levels of lactose and are usually well tolerated in small amounts.
- Drink milk in moderate quantities. Most people with this condition can tolerate 240 ml of milk per day, but you need to work out your own tolerance level. You can buy milk that has had the lactose broken down, which makes it lactose free.
- Drink full-fat milk because the fats slow the journey of the milk through the intestines and allow the lactase enzymes more time to break down the sugars.
- Avoid low-fat or non-fat milks – they travel quickly through the gut and tend to cause symptoms in lactose intolerant people. Also, many low-fat milk products may contain skim milk powder, which provides a higher dose of lactose.
- Eat foods that contain lactose in combination with other foods or spread them out over the day, rather than eating a large amount at once.
- Soy foods such as soy milk and yoghurt are lactose free, a good source of calcium and a good substitute for milk or milk products.
Foods that may contain hidden lactose include:
- biscuits and cakes (if milk or milk solids are added)
- processed breakfast cereals
- cheese sauce
- cream soups
- milk chocolate
- pancakes and pikelets
- scrambled eggs
- muesli bars
- some breads and margarine (containing milk).
Checking food labels for lactose
If you are trying to avoid lactose, ingredients to look for in lists on food labels include:
- milk solids
- non-fat milk solids
- milk sugar.
Where to get help
This page has been produced in consultation with and approved by:
Australasian Society of Clinical Immunology and Allergy (ASCIA)
Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.