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Lactose intolerance is uncommon in Caucasian children, who usually don’t develop symptoms until they’re at least 4-5 years old. About one in five Hispanic, Asian and African-American children have lactose intolerance, with symptoms occurring at around 3-5 years of age.
If your baby has been crying a lot and has watery, runny poo, you might be thinking he has lactose intolerance. This condition isn’t very common in full-term babies, but if your child is showing typical symptoms, proper diagnosis and treatment is important.

What is lactose intolerance?

Lactose intolerance happens when the body can’t break down a sugar called lactose, which is present in all breastmilk, dairy milk and other dairy products.

Lactose makes up around 7% of breastmilk (and a similar amount in infant formula). Lactose provides around 40% of your baby’s energy needs, helps her absorb calcium and iron, and helps ensure healthy development.

Usually, the enzyme lactase, which is produced in the small intestine, changes the lactose into glucose and galactose – sugars that are more easily absorbed. Sometimes babies don’t produce enough lactase to break down all the lactose, so the unabsorbed lactose passes through the gut without being digested. Undigested lactose irritates the gut and causes build-up of wind and diarrhoea.

Most children or adults who are diagnosed with lactose intolerance can digest small amounts of lactose. Generally, 8-10gm of lactose won’t cause symptoms.

Causes of lactose intolerance

There are two types of lactose intolerance: primary and secondary.

Primary lactose intolerance happens when babies are born with no lactase enzymes at all. This is genetically carried and extremely rare. In order to thrive, babies who have this condition need a special diet from the time they’re born.

Secondary lactose intolerance can occur if a child’s digestive system is disrupted by illness, affecting healthy production of enzymes like lactase, or if there’s not enough lactase being produced. Illnesses that might lead to secondary lactose intolerance include tummy bugs that cause gastroenteritis and coeliac disease

Gastroenteritis can cause temporary irritation to the lining of the stomach and small intestine, but this will usually clear up:

  • in around eight weeks in babies under three months
  • in around four weeks in babies older than three months
  • in around one week in babies 18 months and older.

Secondary lactose intolerance caused by not enough lactase being produced usually develops after the age of three. Some people are more likely to develop it than others. For example, people from a Northern European background are generally less likely to develop it. Indigenous Australians and people from Asia and Africa are more likely to get it.

Sometimes lactose intolerance is confused with other digestive problems, such as a food allergy or lactose overload. This is because these conditions have similar symptoms. Food allergies and lactose overload aren’t the same as lactose intolerance, and don’t affect a baby’s production of lactase. There’s more information on food allergies and lactose overload below.

Common symptoms of lactose intolerance

Without lactase, the lactose in milk doesn’t get absorbed and stays in the intestines. As bacteria in the gut feast on the lactose, they produce large amounts of gas. This causes a range of symptoms including:

  • wind
  • pain and swelling in the tummy
  • crankiness
  • failure to settle
  • at feeding times, coming on and off the breast
  • failure to gain weight
  • diarrhoea.

Frothy green diarrhoea happens because unabsorbed lactose forces the intestines to retain excess water.

Another possible side effect is what’s called ‘perianal excoriation’. This is when the gut bacteria break down lactose, converting it to hydrogen and lactic acid. This makes your baby’s bowel movements very acidic, which can cause cuts or abrasions on her sensitive skin. You should put a good protective cream on your baby’s bottom if this happens.

Even if your child has these symptoms, it doesn’t mean he’s lactose intolerant. Some or all of these symptoms are common in healthy breastfed infants, according to research. The symptoms can occur in the first week of life and last up to six weeks or as long as five months. It’s also highly likely the symptoms will disappear. As long as your baby’s weight and health aren’t suffering, it’s not likely there’s a problem.

Note: lactose intolerance doesn’t cause vomiting, but food allergies do.

It’s always wise to consult your doctor if your child has diarrhoea that isn’t getting better, especially if she’s under three months old.

Diagnosing lactose intolerance

Because the symptoms for lactose intolerance and food allergy are similar, diagnosing lactose intolerance can sometimes be tricky.

Methods used to diagnose lactose intolerance include the following:

  • Clinitest tablet: this is when a small amount of poo is mixed with water, then a special tablet is added and checked for colour change. This is mostly used when temporary lactose intolerance is suspected after gastroenteritis.
  • Hydrogen breath test: this tests the amount of hydrogen gas in the child’s breath. Lactose-intolerant children will have higher levels of hydrogen in their breath, because of the process of fermentation in the gut (when bacteria feeds on the lactose that hasn’t been broken down).
  • Elimination diet: this involves removing foods containing lactose from the child’s diet to see whether symptoms improve. If the symptoms come back once the foods are reintroduced, lactose intolerance is most likely the cause of the problem.
Even if your baby’s diagnosed with lactose intolerance, he’ll continue to thrive once yu sort out the problem. Seeking medical guidance for your baby’s nutritional needs is important.

What to do about your child’s lactose intolerance

The treatment for lactose intolerance can depend on the cause. If your child has primary lactose intolerance, your doctor, paediatrician or nutritionist will help guide you.

For secondary lactose intolerance caused by gastroenteritis:

  • try using Lactaid drops that contain the enzyme lactase – but note there’s some debate about the effectiveness of this treatment
  • alternate your baby’s breastfeeds with a lactose-free infant formula. If the situation is particularly serious, you might have to wean your baby onto the formula for a while. If this happens, you can express breastmilk to keep up your supply.

If you’re breastfeeding, persist if possible. Because of the nutritional value of breastmilk, and the benefits of lactose for your baby’s growth, weaning isn’t recommended. And if your child can tolerate a small amount of lactose, gradually increasing it can help her body produce more lactase. 

One of the most important things you can do is soothe and comfort your baby when he’s showing symptoms.

Talk to your doctor if you’re thinking of replacing or alternating breastmilk with a soy-based or other lactose-free formula. You can also talk to a community nurse or lactation consultant if you’re concerned about alternating breastfeeding and bottle-feeding.

Lactose intolerance and diet

If your child is older and diagnosed with lactose intolerance, here are some tips. These also apply to adults with lactose intolerance.

Foods that are OK Foods to watch out for Check the ingredients
  • Bread and cereals
  • Rice and pasta
  • Fruit and vegetables
  • Meat, fish, chicken, pulses, legumes, nuts
  • Cheeses with very small lactose content: brie, camembert, cheddar, colby, cotto, edam, fetta, gouda, havarti, mozzarella, parmesan, Swiss, Tilstat
  • Soy yoghurt
  • Milk, yoghurt, ice-cream, milk desserts, cream cheese, processed cheese, cheese spread, cottage cheese, ricotta
  • Yoghurt-coated muesli bars
  • Instant mashed potato and vegetables with added milk, white or cheese sauces
  • Fish pastes, meat pastes, frankfurts
  • Creamy Italian or French cooking
  • Biscuits
  • Cakes
  • Cake mixes
  • Creamed soups
  • Mayonnaise
  • Milk chocolate
  • Flavoured chips and cheese
  • Flavoured snacks
  • Artificial sweeteners

Here’s a quick reference chart for the lactose content of common foods.

Dairy product Lactose content
Yogurt, plain, low-fat, 240 ml (1 cup) 5 gm
Milk, reduced fat, 240 ml 11 gm
Swiss cheese, 28 g (1 oz) 1 gm
Ice-cream, 120 ml (½ cup) 6 gm
Cottage cheese, 120 ml 2-3 gm
Butter, 20 g (1 tblsp) 0.2 gm
Cream, 20 g (1 tblsp) 0.6 gm

Diet tips

  • In addition to water, rice milk and diluted fruit juice, use a calcium-fortified soy drink or lactose-free milk.
  • Check margarine labels for milk-free varieties.
  • When cooking, try roasts, grilled vegetables and Asian-style stir-fries.
  • For dessert, try lemon sorbet, frozen fruit desserts, meringue, fruit baskets and milk-free muffins.

Lactose overload

Lactose overload isn’t the same as lactose intolerance – that is, it’s not a problem with the production of lactase. Rather, lactose overload occurs when a baby consumes large amounts of lactose at one time and can’t break it all down.

Lactose overload can occur when:

  • bottle-fed babies drink a lot of milk
  • mothers have a natural oversupply of breastmilk in their baby’s early weeks
  • breastfed babies feed frequently and alternate breasts before the breasts have been emptied
  • breastfed babies have a pattern of short breastfeeds – sometimes mothers (understandably!) shorten breastfeeds because of problems such as sore nipples or mastitis
  • breastfed babies drink more first milk than last milk. The first milk passes through the digestive system faster than the last milk – so quickly, in fact, there’s not enough time for all the lactose to be broken down. This can happen when babies aren’t correctly attached to the breast, resulting in longer feeding times but less milk, so the baby gets too much early milk.
Research shows that the symptoms of lactose overload improved in 79% of babies who were fed in a position that ensured they received all the milk from each breast, finished the first breast before moving onto the second breast, and were fed at three-hour intervals (not more frequently), in case of over-feeding. You might like to read more about breastfeeding problems and solutions.

Food allergy versus lactose intolerance

Sometimes symptoms we think indicate lactose intolerance are actually caused by a food allergy. An allergy to milk, for example, affects bottle-fed babies more than breastfed babies because the majority of infant formulas are based on cow’s, goat’s or soy milk.

It’s very rare for babies to be allergic to human breastmilk. But an allergy might develop from proteins eaten by a breastfeeding mother, which are then transferred to her baby via her breastmilk. An elimination diet can be used to diagnose such an allergy. This involves removing dairy foods such as milk, cheese, yogurt and cream from the mother’s diet. If the baby’s symptoms improve but then return when mum reintroduces the foods, this might suggest an allergy.

Reactions to food allergies are more severe than allergies to lactose intolerance. If your baby’s allergic to food such as cow’s milk, soy products or egg, you might notice the following symptoms:

  • vomiting
  • blood or mucus in his diarrhoea
  • poor weight gain
  • wheezing or asthma.
  • Last updated or reviewed 30-12-2010