Lactose intolerance in babies

Lactose is a sugar naturally found in milk and most other dairy products. To digest lactose, the body breaks it down using lactase, a digestive enzyme produced in the gut¹. Lactose intolerance occurs when the body is unable to produce enough lactase, resulting in a number of unpleasant symptoms after eating any foods containing lactose. It’s important to know that lactose intolerance isn’t a milk or food allergy². 

There are three main types of lactose intolerance³:

This occurs when the body’s natural lactase production decreases. This could be because of age, or in response to reducing the amount of dairy products that you eat. A primary lactose intolerance is very uncommon in babies under two years of age, as they’re still likely to be consuming plenty of milk through breast or formula feeding.

An often temporary intolerance to lactose, this is caused by damage to the gut, because of a stomach bug or infection, undiagnosed coeliac disease, or a long course of antibiotics, for example.  

Sometimes, if your baby has been unwell with gastroenteritis, this can result in lactose intolerance. If your child has been diagnosed with gastroenteritis, and they’ve been experiencing diarrhoea for longer than two weeks, then it’s worth having a chat with your GP to rule out lactose intolerance⁴.

This is a very rare, genetic form of lactose intolerance, where babies are born without, or with very low amounts of, lactase due to a genetic fault they inherit. 

If your baby was born prematurely, they may be more susceptible to lactose intolerance because their small intestine isn’t developed enough at birth. However, in most cases, this condition usually improves as your baby gets older.

As we’ve said above, the signs of lactose intolerance in babies can be similar to those of other conditions, meaning that it’s sometimes hard to identify. However, common symptoms include2:

• Tummy pain and rumbling.
• Diarrhoea.
• Bloating of the tummy.
• Excessive wind.
• Vomiting.

Your baby’s symptoms can start anywhere between a few minutes and a few hours of them consuming food that contains lactose¹.  

Because the symptoms of lactose intolerance are so similar to those of a cow’s milk protein allergy, it can be very difficult to distinguish one from the other. They are, however, different.

Whereas a cow’s milk protein allergy is caused by an immune reaction to the proteins that milk contains, lactose intolerance is caused when the body doesn’t produce enough lactase​⁵.

If you’re concerned that your baby has either a cow’s milk protein allergy or is experiencing lactose intolerance, always seek guidance from your GP, who may refer your baby to a dietician to help you manage your baby’s condition.

Whilst loose, watery stools are common in babies with lactose intolerance, they can be a symptom of other things, too. As such, if your baby starts having runnier poos than usual, this doesn’t necessarily mean that they're lactose intolerant.

Remember that it’s not unusual for newborn babies to have the odd runny poo, and every baby is different when it comes to their pooing habits. Once you get to know their toilet habits, you’ll know what’s normal, and what’s not so normal, for your baby. Take a look at our poop chart to learn more.

If you think your baby is having digestive trouble, you should visit your GP who can help with a diagnosis. It might be that your baby is referred to a paediatric dietician for more expert care. 

If you suspect that your baby is lactose intolerant, you shouldn’t make any changes to your baby’s diet unless instructed to do so by your doctor or other healthcare professional. This is because it’s important to ensure that your baby continues to get all the nutrients they need. Of particular importance is calcium, which the body often gets from food which also contains lactose. If there’s insufficient calcium in the diet, this can affect normal bone development³.

Any recommended treatment will depend on how severe your baby’s lactose intolerance is. It might be that your baby is able to tolerate small amounts of dairy and other foods containing lactose without experiencing any symptoms at all².

If you’re breastfeeding, you should continue doing so, as it has numerous benefits for both you and your baby. It’s worth knowing that the amount of lactose in your own diet isn’t related to your baby’s intolerance, so eliminating lactose from your diet won’t make a difference here. If you think your baby may be reacting to the lactose in your breast milk, the best thing to do is seek advice and guidance from your GP.

If your baby is formula fed, your GP or paediatric dietitian may recommend a lactose-reduced or lactose-free infant formula milk for your baby.

If a lactose intolerance is managed and your baby is monitored, it won’t affect their development. Identifying lactose intolerance early means that your baby will feel well again and get the nutrients they need for this stage of their development and their future growth.

Because lactose is found in so many food staples, you might be wondering just how much lactose some of them contain. Take a look at the lactose levels of some common foods⁷:

• Glass of milk (100ml) - 4.6g lactose
• Yogurt whole milk (100g) - 4.7g lactose
• Cheddar cheese (100g) - 0.1g lactose
• Cottage cheese (100g) - 3.1g lactose
• Rice pudding (100g) - 3.9g lactose

Other types of food may contain lactose, too – breakfast cereals being a good example. If your baby has lactose intolerance, be sure to check the ingredient list of any of the foods your baby eats to establish whether they’re suitable.

Depending on the cause, your baby may fully recover from a lactose intolerance, or be able to tolerate more lactose in their diet in the future. For example, symptoms of secondary lactose intolerance if your baby has had gastroenteritis normally disappear within six to eight weeks⁴.  In most cases, lactose intolerance in babies is temporary.

If, on the advice of a medical professional, your baby has been following a lactose-free diet, it may be that your GP or paediatric dietician advises the reintroduction of lactose at some point. This is to test your baby’s reaction and see if there’s been any change. Be sure to keep in touch with your health professional and keep them in the loop about how your baby is getting on.