Lactose Intolerance in Babies

Lactose is the main sugar found in breast milk. It is produced in the breast, it doesn’t come from a mother’s diet. Lactose is very important for the normal health and development of human babies. It provides about 40% of a baby’s energy needs, helps with calcium and iron absorption, keeps pathogenic bacteria in the gut at bay, and is important for development of the large and complex human brain and central nervous system 1.

Lactose intolerance in babies

Lactose intolerance is the inability to digest lactose. True lactose intolerance is very rare in babies because breast milk (which is full of lactose) is the biologically normal food and babies are usually well adapted to digest it by producing special enzymes.

Is lactose intolerance the same as cows’ milk allergy?

No. Having a reaction to traces of cows’ milk protein that enter breast milk via the mother’s diet is not the same as lactose intolerance. Lactose intolerance and milk allergy could both be present at the same time but they are different things. Eliminating lactose from a mother’s diet won’t help the symptoms of lactose intolerance because lactose is added to breast milk in the breast. However, if the real issue is sensitivity to cows’ milk protein then avoiding lactose probably will help the symptoms because cows’ milk proteins and lactose tend to be found in the same foods.

Types of lactose intolerance in babies

Babies are either born with lactose intolerance due to a metabolic disorder (a rare but serious risk to health) or they can get a temporary form of it with several possible causes (much less serious). Different names are used for the different types of lactose intolerance and these vary slightly between authors.

#1 True lactose intolerance

(also called primary or congenital lactose intolerance)

A specific enzyme called lactase breaks lactose down into glucose and galactose (more sugars). It is produced in tiny folds (called brush borders) in the lining of a baby’s intestine. There are a few rare metabolic disorders that mean a baby doesn’t produce enough of this enzyme. True lactose intolerance is very rare, but when present it will be diagnosed within a few days of birth due to the severe and serious symptoms like vomiting, diarrhoea, jaundice and failure to thrive (Kelly Bonyata, 2011). Your health professionals will advise on a special diet for your baby.

#2 Lactose overload

(also called secondary or temporary lactose intolerance.)

If there is too much lactose available for the enzyme to digest, symptoms of wind (gas), tummy ache and copious frothy green or watery stools may be seen. This is much more common than “true” lactose intolerance. The rest of this article discusses causes, symptoms and remedies for this type of temporary lactose intolerance in babies.

What causes lactose overload?

Anything that prevents lactose being digested properly in the intestines can cause lactose overload. This might be damage to the special cells that produce the enzyme in the intestine, or if the volume of low fat breastmilk passing through the intestines floods the enzyme available.

Damage to the intestinal lining

If there is any damage to the intestinal lining it can affect the production of the enzyme lactase which is produced in the delicate brush borders of the intestines. Types of damage include inflammation (e.g. irritation from cows’ milk allergy or gluten) or bacterial or viral infection (e.g. gastroenteritis). Other possible causes of damage include partially digested formula, parasites, and some mothers notice a connection with live vaccines such as rotavirus (Minchin, 2015). If there is not enough enzyme, large amounts of lactose can pass undigested to the lower bowel. Here it will be fermented by bacteria giving the familiar symptoms of gas, discomfort and lots of green watery stools.

Damage to the brush borders may take some time to heal. Joy Anderson says:

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.

Too much lactose

A big breast milk feed with a high lactose content but low fat content can pass through to the lower bowel too quickly without being digested properly. A higher fat content slows the time in the bowel giving time for proper digestion. This leads to the same colic type symptoms of wind (gas), tummy ache and green or watery stools (Anderson, 2012).


Some premature babies might not produce enough lactase until they mature. This is known as developmental lactase deficiency (Mohrbacher, 2010; Kelly Bonyata, 2011).

What causes lactose intolerance in adults?

In many cultures across the world, levels of the enzyme lactase start to fall after three to seven years of age (to correspond with weaning). They often fall so low (particularly in non-Caucasian groups) that an individual may become lactose intolerant (unable to digest lactose). This may not happen until adulthood. This is not the same as lactose intolerance in babies (Anderson, 2012, Wambach & Riordan, 2015). Mohrbacher, 2010 reserves the name primary lactose intolerance for this adult type.

Lactose intolerance in babies

Symptoms of lactose overload in babies

Good weight gain but windy, unsettled, lots of poop

A baby with lactose overload might typically gain weight very well but show several of the following colic type symptoms:

  • Very windy 2
  • Loads of explosive green3 or yellow frothy, foamy or watery poop
  • Tummy ache or “colic”
  • Unhappy, unsettled baby
  • Nappy rash
  • Mucousy poop

Poor weight gain is possible

Not all babies continue to gain weight well and some may even fail to thrive as the milk is passing through the gut too quickly to be digested and absorbed;

Some babies lose so much weight from the rapid passage of all food that they fail to thrive, although the mother often has a booming milk supply from all the stimulation, needing breast pads to mop up leakage.

Blood in the stools?

Constant irritation to the intestines may also give rise to small amounts of bleeding in the stools. Diana West IBCLC explains:

Over time, large amounts of undigested lactose can irritate the lining of the intestines so that even a little bit passing through can cause irritation. Occasionally, this can result in small amounts of bleeding into stools that can be misdiagnosed as a food allergy. Some pediatricians will mistakenly diagnose lactose intolerance if there is undigested sugar in the baby’s stool.

Evening colic

Some breastfed babies seem to have colic type symptoms every evening at a set time but are quite cheerful the rest of the day or night. Author Maureen Minchin hypothesises that this could be due to ‘lactose overload’ from the first feed in the morning i.e. when this is a low fat, large lactose load on a relatively empty tummy (Milk Matters, 2015).

Answers to lactose overload

Finding the reason for lactose overload and knowing what to do about it will usually improve the symptoms without needing to stop breastfeeding. To help find the right answer for you from the ideas below ask your IBCLC lactation consultant for help.

Finish the first breast, offer the second

The fat content of breastmilk increases during a feed and also increases the closer together the feeds are. If a mother is shortening feeds (perhaps because of painful nipples) or feeding on a schedule it can lower the fat content in breastmilk. Less fat increases the time spent in the stomach (gastric clearance time) resulting in the lactose passing through the stomach and bowel without being properly digested. This causes symptoms of lactose overload (Noble & Bovey, 1998; Jack Newman, 2009). Finishing the first breast before offering the second side will help your baby to get the higher fat milk he needs.

Continue to breastfeed

Jack Newman, Canadian paediatrician and breastfeeding expert, discusses breastfeeding management in more detail in Colic in the Breastfed Baby. He explains that the best way to deal with lactose overload is to improve the baby’s latch, know how to spot when a baby isn’t really swallowing milk, to use breast compressions before switching sides and then offer the second breast and repeat. He advises

If the baby is gaining well and drinking well, this too will pass. It’s worth continuing to breastfeed and not putting the baby on formula.

Stay on one breast if needed

If a mother has a very large storage capacity she may need to feed from one breast per feed so that her baby can get a good balance of higher fat milk. Jack Newman explains (with a caution!):

In some situations where the baby is colicky from getting too much milk too quickly, and fixing the latch and finishing one side before offering the other breast does not work, it may be worthwhile to try giving one breast at a feeding or even two feedings in a row. The mother needs to be aware that this may cause her milk production to decrease, and that the baby may fuss because he’s not getting as much milk as he wants—even if he is still gaining weight well.

Be flexible

Feeding plans such as block feeding (staying on one breast per feed or for a set period of time) need to be flexible. Just because a baby wants one breast in a morning may not be the case by the evening when he might need both breasts per feed. Similarly what works at two months of age to cure fussy behaviour may need changing in a few weeks time or during a growth spurt. Another good quote from Colic in the Breastfed Baby:

It is not a good idea to feed the baby on just one side, to follow a rule. Yes, making sure the baby “finishes” the first side before offering the second can help treat poor weight gain or colic in the baby, but rules and breastfeeding do not go together well. If the baby is not drinking, actually getting milk, there is no point in just keeping the baby sucking without getting any milk for long periods of time. You should “finish” one side and if the baby wants more, offer the other.

Not enough milk?

An unhappy baby with scant green nappies may not be getting enough milk rather than the problem being milk allergy or lactose overload. Sometimes a fussy baby who seems to want to feed a lot is just “hanging out” at the breast but not getting enough milk. Advice to stay on one breast per feed or for several feeds is not appropriate here. Your IBCLC can help you decide what is going on and see How to Make More Breast Milk for lots of ideas to increase your milk supply.

Jack Newman points out on his Facebook page:

Many babies diagnosed with “allergy” to something in the milk get better when put on special formulas. Why? Not because they are no longer exposed to the mother’s milk, but rather because now the baby gets more milk.

Mother’s diet

Although lactose is produced in the breast, and the amount of lactose containing foods a mother eats won’t make a difference to the lactose content in breastmilk, Noble and Bovey suggest inadequate fat in the mother’s diet can make lactose overload worse in her baby and they give suggestions for dietary changes. Also, if a baby is sensitive to cows’ milk protein (in breast milk via mother’s diet) this may cause inflammation and irritation to baby’s gastrointestinal tract which can then cause symptoms of lactose overload. If this is the case see Elimination Diet for further reading.

Lactase drops

There are anecdotal reports that drops containing the enzyme lactase can be used to predigest lactose in expressed milk (Joy Anderson, 2012).

My doctor said I should stop breastfeeding

Some doctors are confused about lactose intolerance, milk allergy and colic. They may recommend lactose-free formula or newer ‘special’ formulas. However the answer to most cases of temporary lactose intolerance is to get help with breastfeeding rather than switch to industrial formulas (Jack Newman p 177 & 181).

Laid back breastfeeding

What about too much foremilk, oversupply or a fast let down?

Before blaming any of these as causes of lactose intolerance talk to your IBCLC about the best way forward after they have taken a full history, looked at your baby’s weight chart and watched your baby feeding. For more reading on oversupply or a fast let down (milk ejection reflex) see Oversupply of Breast Milk and Jack Newman’s Colic in the Breastfed Baby. For more understanding about foremilk and hindmilk see Forget About Foremilk and Hindmilk.