Understanding lactose in breast milk: your complete guide

Breast milk is a truly amazing thing. Designed especially for your baby from the moment they’re born, it’s packed with the water, fat, and essential vitamins, minerals, carbohydrates and proteins that they need¹.

But does human breast milk have lactose in it? And if so, what benefits does this have for your little one?

Welcome to your complete guide to lactose in breast milk, where we’ll cover everything from what lactose is and why it’s important, to spotting the signs of lactose intolerance.

Yes, it does. On average, every 100ml of your breast milk contains around 7g of lactose², and it’s the most plentiful nutrient that your breast milk contains³.

Lactose is the primary carbohydrate found in your breast milk. It’s a natural sugar found in milk - your breast milk included. It’s made up of two types of sugar called glucose and galactose. The enzyme lactase (produced by your small intestine) breaks lactose down into these two sugars so your body can absorb it properly⁴.

Lactose provides your baby with around 40% of the calories they need⁵. This makes it their main source of energy for all that wriggling, playing, and moving around!

So, your breast milk contains lactose, but what benefits does it bring for your baby as well as providing energy? Let’s take a look. 

• Supporting tiny tummies: Lactose is a carbohydrate that supports a healthy balance of bacteria in your little one’s gut⁶.
• Helps to build immunity: Babies don’t absorb all of the lactose in your breast milk. What’s left over acts as a prebiotic, encouraging the growth of friendly bacteria and potentially helping to support your baby’s immune system⁷.
• Helps your baby absorb other minerals: When it ferments in the large intestine, lactose helps your baby absorb calcium and magnesium by making them more soluble⁸.
• Brain development: Some studies have shown that lactose in breast milk helps to promote the development of your baby’s brain and support memory and learning⁹.

There’s a lot more to your breast milk than you might think - it’s pretty amazing stuff!

During each feed, the content of your breast milk changes, and your baby will benefit from both foremilk and hindmilk¹⁰:

Foremilk: Your breasts produce foremilk at the beginning of a feed. It’s thinner, flows more quickly, and has a higher water content. There’s also more of it, and it tends to have a lower fat content than the hindmilk that comes towards the end of a feed. Foremilk is full of proteins and carbohydrates, both of which are essential for your baby’s growth and development. 

Hindmilk: As your baby feeds, your breasts produce hindmilk. This isn’t a different type of milk, but rather your breast milk becomes less in volume, thicker and richer in fat. 

Both your foremilk and your hindmilk contain lactose, and the lactose content doesn’t change as you breastfeed your baby. The main difference is the fat content, which changes as the feed goes on³. 

No, it doesn’t. Your body makes lactose in order to feed your baby - it’s not something you pass on from your diet. The amount of lactose contained in your breast milk won’t change whether you reduce the amount of dairy you eat or remove it from your diet completely^{12, 13}.

Whilst lactose intolerance is a fairly common problem worldwide, it’s rare in children under 5 years old¹⁴. However, babies can occasionally experience lactose intolerance, so it’s good to know what it is and spot the signs so you can seek the advice you need.

Lactose intolerance happens when the body doesn’t make enough lactase enzyme to break it down. Symptoms include15:

• Tummy discomfort
• Excessive wind 
• Watery and/or green, sometimes explosive, diarrhoea 

Whilst your breast milk contains lactose, this doesn’t necessarily mean that you’ll need to stop breastfeeding, and any changes you’ll be advised to make depend on the type of lactose intolerance your little one has. That’s why it’s important to seek medical advice before making any changes to your baby’s feeding routine.

Sometimes, babies can experience lactose overload.

During breastfeeding, the level of fat in your milk increases as your baby feeds. This fat is very important for your baby, as it slows the flow of milk through their gut, helping them to digest lactose. If your baby gets too much foremilk and not enough hindmilk when they breastfeed, this can lead to a lactose overload. There are a number of reasons why this might happen. You might have a high milk supply, for example, or be switching breasts too soon during a breastfeed^{13, 16}:

The symptoms of lactose overload are very similar to those of lactose intolerance, including excessive wind, green and runny poo, and tummy pain. 

If you’ve got any questions or concerns about your milk supply, always speak to your healthcare professional or a lactation specialist for advice.

An extremely rare, severe type of lactose intolerance is called congenital lactose intolerance, which is caused by a genetic defect. If your baby has this type of intolerance, they’ll need specialised care to manage symptoms like severe diarrhoea and ensure they’re getting all the nutrients they need¹⁷.

Primary lactose intolerance is also genetic but is less severe than congenital lactose intolerance. Babies are designed to be able to digest lactose because it is an important energy source in breast milk. This is less important as we grow up, so the production of the lactase enzyme can start to decline after the age of 5 years and into adulthood in some people. This is more common in populations that don’t traditionally eat dairy products. It’s less common in Northern Europeans where dairy is a key part of the diet. Most people with this type of lactose intolerance can tolerate some lactose spread across the day in smaller portions¹⁷.

Secondary lactose intolerance is the third type, and this is the most common type seen in infants and young children. It’s called ‘secondary’ as it is a temporary form of intolerance that results from inflammation of the gut lining caused by an infection (like gastroenteritis) or another condition that reduces or stops the production of lactase. Once the infection is treated and the gut heals, then lactase production is resumed. Sometimes lactose intake needs to be reduced for a few weeks while the gut repairs, but it can be reintroduced again once everything has settled. You should always get medical advice before making any changes to your baby’s feeding routine as it is important that lactose intolerance is correctly diagnosed and managed.

Lactose intolerance isn’t the same as CMPA. Lactose intolerance is caused by the lactase enzyme being absent, or your body being unable to digest lactase (the sugar in milk) - it has nothing to do with the immune system¹⁸.

A cow’s milk protein allergy, on the other hand, is the result of an immune reaction to the protein found in cow’s milk¹⁹. Symptoms of a cow’s milk protein allergy include²⁰:

• Itchy, red skin (your baby may come out in hives or have eczema)
• Sneezing and a runny nose
• A cough, shortness of breath or wheezing
• Vomiting, diarrhoea or constipation and tummy pain
• Swelling around the mouth or face, or other parts of the body

If you’re breastfeeding, tiny amounts of cow’s milk protein can pass into your breast milk through the foods you eat but CMPA is much less likely in breastfed babies²¹. 

If you suspect that your baby has a CMPA, you should speak to your healthcare professional before making any changes to your baby’s feeding routine. That way, you’ll be able to get the correct diagnosis and advice about how to manage your baby’s symptoms.

When it comes to feeding your baby, it’s good to have the information you need and the answers to any questions you might have. We’re always here to help, but it’s also important to know when you should seek medical advice and support. 

If you suspect your baby is lactose intolerant, you should always contact your doctor if they experience any of the following¹⁸:

• Weight loss
• Symptoms that don’t ease and keep coming back
• Changes to their poo - for example, looser stools, pooing more frequently, constipation, or you see blood in their poo. 
• Tummy pain or discomfort and bloating that’s been happening for longer than 3 weeks