Lactose Intolerance – 4 Facts About Intolerance In Babies

Lactose is the most abundant component of human milk.

It has been found to serve as an anti-infective factor, to enhance calcium and iron absorption, be a building block of prebiotics in breastmilk and support healthy brain and central nervous system development.

The lactose concentration in breastmilk is about the same from the start to the end of a breastfeed.

Also, how much lactose (e.g. in dairy products) a mother consumes in her diet does not reflect the amount of lactose in her breastmilk.

Here are 4 facts about lactose intolerance in babies that help explain the ‘why’ and ‘how’ it can occur:

#1: Congenital Lactose Intolerance Is Rare

It is very rare for a baby to be born with congenital lactose intolerance. This is where a baby is born with a lack in lactase (the enzyme that digests lactose). A baby with congenital lactose intolerance would fail to grow well from birth and requires a specialised lactose-free formula.

#2: Most Cases Of Lactose Intolerance Occur Due To Something That Has Irritated The Gut

Lactase sits on the tip of the microscopic folds in the gut (the villi). So, anything that causes gut irritation (and disrupts these villi) may reduce the amount of lactase and hence cause secondary lactose intolerance.

Here are some of the causes of secondary lactose intolerance:

  • Gastroenteritis
  • A food sensitivity
  • A parasitic infection
  • Coeliac disease
  • Crohn’s disease
  • Bowel surgery

Anecdotally, some mothers have found their baby gets a temporary case of secondary lactose intolerance following them having the oral rotavirus vaccine or after antibiotic use.

Symptoms of secondary lactose intolerance in an exclusively breastfed baby are:

  • Green frothy/very liquid bowel motions
  • Irritability (i.e. sleeps little, cries a lot)
  • Is very ‘windy’

#3: Symptoms Of Secondary Lactose Intolerance Are Common With Lactose Overload

It is important to recognise that the above symptoms are also common in a baby with lactose overload due to the mother having an oversupply. A baby with lactose overload (as opposed to a baby with secondary lactose intolerance) will also typically:

  • Be under 3 months of age
  • Have a large output
  • Have an average to above-average weight gain
  • Have a mother with an oversupply

#4: Substituting Breastmilk With Lactose-Free Formula Is NOT The Solution

The solution for a breastfed baby with secondary lactose intolerance is not to stop breastfeeding or go onto a soy or lactose free formula. These formulas should be recommended only if the baby is already fed formula or there are concerns about her growth.

The solution is to find out what caused the secondary lactose intolerance and deal with that. Breastmilk can help the gut to heal. So in the case of there being something that has irritated the gut, we want breastfeeding to continue.

When the cause of the secondary lactose intolerance resolves, the gut heals and the intolerance goes away. For example, if the cause of an exclusively breastfed baby’s secondary lactose intolerance is a cow’s milk protein allergy, if the mother eliminates cow’s milk protein from her diet, the secondary lactose intolerance in her baby will disappear. Even if it’s not picked up that a baby is lactose-intolerant, continuing to breastfeed will not harm your baby as long as she is otherwise well and growing normally.

For a formula fed baby with lactose intolerance secondary to a cow’s milk protein allergy, a lactose free formula may dampen the symptoms but not really heal the gut because a lactose free formula still contains cow’s milk protein. What a formula fed baby with a cow’s milk protein allergy really needs is an extensively hydrolyzed or elemental formula, or in some cases a soy formula may be okay.

If you are worried that your baby may have secondary lactose intolerance, speak to a dietitian who has an interest in breastfeeding (lactation) or infant feeding (see

Last Updated: July 22, 2015


Renee Kam is mother to Jessica and Lara, an International Board Certified Lactation Consultant (IBCLC), a physiotherapist, author of 'The Newborn Baby Manual' and an Australian Breastfeeding Association Counsellor. In her spare time, Renee enjoys spending time with family and friends, horse riding, running and reading.

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