Lactose malabsorption

Primary and secondary lactose intolerance versus lactose overload in infants

Lactose is a disaccharide formed by a bond between the two monosaccharides, galactose and glucose. It is present in all mammalian milk, including human breastmilk. Lactose intolerance is a clinical condition where dietary lactose is poorly digested and absorbed and consequently induces gastrointestinal (GI) symptoms including abdominal pain, bloating, wind and diarrhoea.

Lactose requires the enzyme lactase to break it down into its single sugar units that can be absorbed easily. In some individuals, the production of the lactase enzyme is insufficient to breakdown ingested lactose (primary lactose intolerance) and so malabsorption of the ingested lactose can result in GI symptoms. In others, lactose intolerance can occur due to intestinal injury or inflammation (secondary lactose intolerance), which subsequently affects digestion and absorption of food components including lactose and will result in symptoms.

In infants, the cause of symptoms such as apparent abdominal pain, wind and loose stools (reported frequently in infants) may be attributed to lactose intolerance from the milk they consume, because lactose intolerance is one of the most well documented food intolerances in adults. However, there are many reasons that this association should be questioned and this requires the health professional to consider other potential causes.

Primary lactose intolerance

Primary lactose intolerance in infancy is extremely rare. If present, the infant will not thrive from birth and this presents an extreme medical/nutritional threat. In fact, lactase enzyme production is at its peak in infancy and in those people and ethnic groups at risk of lactose intolerance, enzyme production only reduces from around age five(1)(2,3)

Secondary lactose intolerance

Secondary lactose intolerance is not uncommon in infancy. More important than trying to manage the secondary lactose intolerance by supplementing with lactase enzyme or by switching to a lactose free formula (e.g. one based on soy milk), is to address the cause of the secondary lactose intolerance. This occurs in the setting of inflammation of or injury to the small bowel (e.g. food allergy, infection, gastroenteritis) and requires medical investigation.

Some babies may have an improvement of symptoms when the mother switches them to a lactose free cows’ milk based formula or soy based formula, thereby apparently confirming the suspected lactose intolerance(4)

Lactose overload in breastfed infants

Breastmilk is a rich source of lactose and the lactose content in breastmilk is completely independent of the mother’s dietary lactose intake. So, adjusting a mother’s dairy intake will not change the lactose content of her breastmilk.

In breastfed infants consuming large volumes of breastmilk, symptoms of lactose overload may develop, usually in babies around 3 months of age or younger. Lactose overload can develop when an infant’s mother has an oversupply of breastmilk, but lactose overload does not mean that an infant is lactose intolerant.

However, lactose overload can often be confused with lactose intolerance due to the presentation of similar symptoms.

An infant with lactose overload can present with adequate weight gains, but unsettled behaviour and wind, with many wet nappies per day (>10/day) and stools which are green, frothy and explosive.

Strategies to manage a mother’s breastmilk volume oversupply can be implemented through discussions with an Australian Breastfeeding Association counsellor, International Board Certified Lactation Consultant, paediatric dietitian or other healthcare professional with expertise.

In such cases, when breastmilk is produced in greater volumes, it is lower in fat content and consequently the feed moves through the gastrointestinal tract quickly. This results in the incomplete breakdown and absorption of lactose, which draws water into the bowel and provides substrate for bacteria to ferment, ultimately leading to a lowered pH environment, wind production and softer, more acidic stools.

Of course, this also results in an ‘unsettled’ baby, which may lead to behaviours that a nursing mother can read as signals of ‘hunger’ or as being dissatisfied. In what becomes something like a ‘cycle’, the baby may then want to suck on his/her mother’s breast, which provides comfort as well as breastmilk and can help move gas through the bowel and pass stools. In reality, this creates a cycle of more feeding and breastmilk producing more wind and fluid accretion and discomfort to the infant.

Lactose overload management can be achieved with correct professional advice to a breastfeeding mother, in order to facilitate her ability to manage her breastmilk oversupply. An infant will generally tolerate the lactose present in a smaller breastmilk volume and consequently more concentrated fat content, which then slows transit rate.

Some mothers may be advised incorrectly to cease breastfeeding and introduce a lactose free formula feed. Determining the cause of the symptoms is vital and all too often mothers are under such distress that they manipulate their diet and the diet of their infant without knowledge of the underlying problem. Correct and timely professional advice can turn things around for a mother and her breastfeeding infant and promote the best practice outcome of ongoing breastfeeding.

Find further information


  1. Auricchio S, Rubino A and Murset G, 1965. Intestinal glycosidase activities in the human embryo, fetus and newborn. 35(6), 944-954. External link
  2. Griffin M.P and Hansen J.W, 1999. Can the elimination of lactose from formula improve feeding tolerance in premature infants? 135(5), 587-592. External link
  3. Shulman R.J, Schanler R.J, Lau C, et al., 1998. Early feeding, feeding tolerance, and lactase activity in preterm infants. J Pediatr. 133(5), 645-649. External link
  4. Heyman M.B and Committee on N, 2006. Lactose intolerance in infants, children and adolescents. Pediatrics. 118(3), 1279-1286. External link

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An association between consumption of 3 serves of dairy foods containing A1 beta-casein and digestive discomfort, in some individuals, has been established by a process of systematic review. The NHMRC recommends a healthy diet including up to 4 serves of dairy foods/day.