All gain – what’s actually in my breast milk (& how can I go for gold?)

Breast milk nutrient composition – totally fascinating

I know when I was nursing, breast milk and its incredible blend and balance of macro and micro nutrients – from all those lovely fats to vitamin A, calcium and more, including super-clever ‘live antibodies’ – was totally fascinating. 

However long you breastfeed for, the milk you produce is packed with nutrients that are uniquely designed to nourish and protect your baby, adjusting its composition to meet your little one’s needs as they grow. But what’s really going on inside that liquid gold?

What’s in breast milk? Breaking down the nutrients

Breast milk is loaded with the good stuff, including:

• Proteins: Your baby’s muscles and tissues need these building blocks. Whey and casein are the key players, with whey making up the larger percentage, making it easier to digest for tiny bellies. Special mention to lactoferrin, which helps fight off infections!
• Fats: Think of fats as brain food – literally! These fats, including omega-3s like DHA, are crucial for your baby’s brain and eye development. Plus, they’re the primary energy source.
• Carbohydrates: Enter lactose, the sugar that fuels your baby’s body and helps with healthy gut bacteria growth. These carbs are gentle on their digestive system.
• Vitamins & minerals: From vitamin A (great for vision) to calcium (hello, strong bones!) and iron (keeps their blood cells happy), breast milk provides for your baby’s needs in the right amounts. These essential micronutrients support everything from immune function to cell growth.

Nutrient composition of human breast milk

This is my favorite part –  did you know that the nutrient composition of breast milk isn’t static? It changes based on your baby’s age, and even adapts to the time of day or whether your baby is sick. Breast milk for preterm babies, for example, contains higher levels of fat and proteins to give premature infants the extra boost they need for development.

Even more amazing is how breast milk’s components evolve over time. Early on, you’ll produce colostrum, a thicker, nutrient-rich form of breast milk that’s packed with antibodies. This ‘first milk’ is a powerhouse of immunity. Later, as your baby grows, the balance of proteins, fats, and carbohydrates adjusts to fit their needs.

Keen on colostrum? Read our guide to colostrum harvesting for all the intel on this nutrient-dense first milk.

What’s in breast milk that’s not in formula?

First off, at TRB we are advocates of fed is best. Your baby being fed and developing well, and your own wellbeing as a parent are paramount. But if we’re drilling into key differences, a few to note are: 

• live antibodies – these help protect your baby from infections 
• enzymes and hormones like leptin, which helps regulate appetite and metabolism 
• unique sugars (called oligosaccharides) that promote the growth of healthy gut bacteria

In lab conditions, you’d also see subtle differences between vitamin and mineral content, depending on your own unique breast milk composition and the brand of formula you’re using.

Which micronutrients are in breast milk?

Alongside big players like fats and proteins, breast milk delivers a blend of micronutrients, including these essential minerals and vitamins:

• calcium for bone development
• iron, which is easily absorbed to support oxygen transport in the blood
• magnesium, critical for muscle and nerve function
• zinc, essential for a healthy immune system and growth
• vitamin A, which supports vision and immune function
• vitamin D – important for calcium absorption, although supplementation may be needed in some cases
• vitamin B12 – key for brain development and nerve function

Micronutrient levels can vary depending on your diet, which is why eating a balanced diet while breastfeeding is so important. 

A fantastic starting point would be the lactation cookie recipe I swear by postpartum (and the one I use for all my nursing mama friends too – it’s so easy to make up a batch!)

Did you know? Breast milk contains about 22 calories per ounce. And with an ideal balance of protein, fat, and carbohydrates designed to support an infant’s growth and energy needs – it really is incredible stuff. 

Whether you breastfeed your baby for one feed, one week, a month or a year, every drop really does count. You’re supporting an incredible and complex process – from gut development to brain health – and whatever your journey, we’re here to support every FAQ. 

Next on your reading list: 5 things to know when breastfeeding, during sickness