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Lactose intolerance and the breastfed baby

By Joy Anderson AM BSc(Nutrition), PostgradDipDiet, APD, IBCLC, ABA Breastfeeding Counsellor 

Lactose intolerance is poorly understood in the Australian community. There are lots of myths and misunderstandings about it, especially when it comes to babies. Contrary to what you may hear:

  • There will not be less lactose in the breastmilk if the mother stops eating dairy products.
  • There is no relationship between lactose intolerance in adult family members, including in the mother, and in babies. They are different types of lactose intolerance.
  • A baby with symptoms of lactose intolerance should not be taken off the breast and fed on soy-based or special lactose-free infant formula.
  • Lactose intolerance is very different to intolerance or allergy to cows' milk protein.

Lactose is the sugar in all mammalian milks. It is produced in the breast. The amount of lactose in breastmilk is independent of the mother's consumption of lactose and hardly varies. The milk the baby gets when he first starts to feed contains much the same amount of lactose as does the milk at the end of a breastfeed. However, the milk at the end does contain more fat.

Lactase is the enzyme that is required to digest lactose. Lactose intolerance occurs when a person does not produce this enzyme, or does not produce enough of it, and is therefore unable to digest lactose. If it is not digested and broken down, it cannot be absorbed. If this happens, the lactose continues on in the digestive tract until it gets to the large bowel. It is here that bacteria break it down to make acids and gases.

The symptoms of lactose intolerance are liquid, sometimes green, frothy stools and an irritable baby who may pass wind often. If a baby is lactose intolerant, the medical tests ('hydrogen breath test' and tests for 'reducing sugars' in the stools) would be expected to be positive. However they are also positive in most normal breastfed babies under 3 months. Their use in diagnosing lactose intolerance in young babies is therefore open to question.

Lactose intolerance in babies

Primary (or true) lactose intolerance

This extremely rare genetic condition is incompatible with normal life unless there is medical intervention. A truly lactose-intolerant baby would fail to thrive from birth (ie not even start to gain weight) and show obvious symptoms of malabsorption and dehydration. This is a medical emergency and the baby would need a special diet from soon after birth.

Secondary lactose intolerance

Because the enzyme lactase is produced in the very tips of the microscopic folds of the intestine, anything that damages the gut lining can cause secondary lactose intolerance. Even subtle damage to the gut may wipe off these tips and reduce the enzyme production, for example:

  • Gastroenteritis.
  • Food intolerance or allergy. In breastfed babies, this can come from food proteins, such as in cows' milk, wheat, soy or egg, or possibly other food chemicals that enter breastmilk from the mother's diet, as well as from food the baby has eaten.
  • Parasitic infection such as giardiasis or cryptosporidiosis.
  • Coeliac disease (intolerance to the gluten in wheat and some other grain products).
  • Following bowel surgery.

Food allergies and food intolerances can cause a baby to be unsettled. The foods to which a baby is allergic or intolerant can pass from through the mother's breastmilk. In some cases, removal from the mother's diet of the foods to which the baby is allergic or intolerant, for example cows' milk products, can sometimes help. If you wish to try eliminating foods from your diet on the suspicion that your baby has an allergy or an intolerance, check with a dietitian to help you identify the culprit foods and to make sure your diet is nutritionally adequate for both you and your baby.

Cows' milk protein allergy (or intolerance) is often confused with lactose intolerance and many people think they are the same thing. This is not the case. The confusion probably arises because cows' milk protein and lactose are both in the same food, ie dairy products. Since allergy or intolerance to a food protein can cause secondary lactose intolerance, they may be present together, further adding to this confusion.

Secondary lactose intolerance is temporary, as long as the gut damage can heal. When the cause of the damage to the gut is removed, for example by taking the food to which a breastfed baby is allergic out of the mother's diet, the gut will heal, even if the baby is still fed breastmilk. If your doctor does diagnose 'lactose intolerance', continuing to breastfeed will not harm your baby as long as she is otherwise well and growing normally.

While the baby has symptoms of lactose intolerance, it is sometimes suggested that the mother alternate breastfeeding the baby with feeds of lactose-free formula or even take the baby off the breast. Authorities only recommend the use of lactose-free formula if the baby is formula-fed and is very malnourished and/or losing weight. However, human milk remains the best food and will assist with gut healing. In addition, sensitivity of the baby to foreign protein (cow or soy) should be considered before introduction of any formula, as regular types, including lactose-free ones, may make this problem worse. You should seek professional advice on the need for hypoallergenic formula. A medical adviser should see any baby with long-term symptoms and/or who is failing to thrive.

Before even partially taking a baby off the breast for a short time, thought should be given to other aspects of the breastfeeding relationship. Questions you could ask include:

  • How will alternative feeding methods affect my baby?
  • Could bottle-feeding other milk products result in breast refusal later?
  • How easily will I be able to express my milk to maintain my supply?

Average recovery time for the gut of a baby with severe gastroenteritis is 4 weeks, but may be up to 8 weeks for a baby under 3 months. For older babies, over about 18 months, recovery may be as rapid as 1 week. If a medical adviser orders alternative feeds for the baby, it is important that the mother understands that her breastmilk is still the normal and proper food for her baby in the long term.

You may have heard about giving drops containing the enzyme lactase to babies who have symptoms of lactose intolerance. There is little evidence that these are of much value when used this way, although there are anecdotal reports that relatively large doses may help in some cases. Lactase products are mainly designed to be added to expressed breastmilk (or other milk) and left overnight for the enzyme to predigest the lactose in the milk. In practice they seem to be occasionally useful for babies. While these products may help reduce symptoms, they do not solve the underlying issue of what is damaging the gut.

Lactose intolerance in adults

Lactase enzyme levels normally change over a person's life span. They rise rapidly in the first week after birth, start to fall from about 3-5 years of age and fall sharply in later childhood. Low levels of lactose in colostrum match the low levels of the enzyme present in the first week of life.

Cows' milk is commonly consumed by adults in some populations, but mostly by people of northern European descent. In about 70% of the people of the world, and in a significant number of Australians, levels of this enzyme fall so low in adulthood that they become lactose intolerant. The tendency to adult lactose intolerance is genetically determined. People with Asian, African, Australian Aboriginal and Hispanic ancestry are more likely to be lactose intolerant as adults. Caucasians are more likely to be able to consume milk as adults because they tend to continue producing the enzyme lactase throughout life. An adult who has very low levels of the enzyme can usually tolerate some lactose because normal bacteria living in the gut provide a limited capacity to break it down. However, the person may find it gives them loose stools and 'wind'.

Human babies of any ancestry can tolerate lactose. In fact, human milk has a very high concentration of lactose compared to cows' milk and that of other mammals. This is thought to be related to a human baby's rapid brain growth in infancy, compared to other mammals. Removing lactose from any baby's diet for more than a short period should not be done lightly and then only under medical supervision.

Lactose overload in babies

Lactose overload can mimic lactose intolerance and is frequently mistaken for it. For more information see the lactose overload article.


As explained above, there are several types of lactose intolerance, but it is very rare for a baby to have to stop breastfeeding because of this condition. Except for the extremely rare primary type, there is always a cause behind lactose intolerance in babies. Getting to the cause and fixing that is the key to resolving the baby's symptoms.


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© Australian Breastfeeding Association Reviewed August 2017


Last reviewed: 
Aug 2017