Breastfeeding Chemistry Part 2: What Is In Breastmilk?

By Ali Weatherford in consultation with Cassie Terrillion, IBCLC

I hear a lot about the latest advancements in technology for infant formula. It’s true that it’s getting better all the time. Scientists are working to make it as close to human milk as possible.

But did you know that human milk substitutes existed WAY before the modern age of baby formula? There have always been situations where a mother was not able to feed her baby.

Whenever possible, another woman in the family or community would breastfeed the baby. But sometimes that was not possible, and humans learned how to substitute human milk with the milk of another mammal. Cow, goat, and sheep milks were used most, but often with bad results because of issues with intolerance, contamination, and poor storage options. Human infants often didn’t survive without human milk.

What’s in Baby Formula?

In 1915, a formula called “synthetic milk adapted” was created using the lactose from cow’s milk and added oils. Cow’s milk was the best option, but the fats needed to be removed and replaced with vegetable oils for the babies to tolerate it better.

Over many decades, modifications were made to infant formula to add to the nutritional value and make it a more complete and healthy option. Iron, whey protein, fatty acids, taurine, nucleotides, carbohydrates, and more have been added and adjusted for this purpose. Today, we have very advanced and nutritious infant formulas available for people who can’t or don’t wish to breastfeed.

While making a nutritious alternative to human milk has been possible, the goal of matching human milk composition exactly is not something that science has been able to do. A baby’s own mother’s milk is most likely something that will never be able to be duplicated. There’s a little bit of magic involved.

The Milk-Making Process

When a baby is born, and the placenta is expelled, the mother’s body begins to do work of a different kind. Most often, a naked baby is put onto her naked skin where she can smell, feel, and see the baby. This, in combination with the hormones of labor and birth, triggers other hormones to be produced that help a body make milk and bond with the baby. This is important so that we have strong instincts to protect and care for the baby, and so that we produce food for the baby.

Nipples darken during pregnancy so a newborn’s weak eyes can easily see it. Glands around the nipple produce an enzyme that tastes and smells like amniotic fluid so it’s familiar and appealing to the baby. The baby has reflexes as a newborn that go away after a few months, and it appears that many of these reflexes were developed to help the baby feed at the breast more easily. When the baby is strong and coordinated enough to feed better later, the reflexes then disappear.

When the baby first attaches to the breast and begins to draw out milk, it only gets a very small amount of a substance called colostrum. A baby’s stomach is very small at birth and can only hold this teaspoon sized amount of food anyway. For this reason, babies need to eat OFTEN at first. This frequent feeding also supports the body’s ability to produce more milk. Milk being drawn out of the body more frequently triggers the body to make more.

Feeding often helps the body establish a supply of milk in the coming days. Colostrum is thick and dense with important nutrients and other important substances. Colostrum is actually pretty low in lactose. But it is rich in components that provide immunity and growth support for babies so they can develop quickly, be protected from infection and illness, and to help their digestive system mature and be able to absorb and use nutrients. The fact that the chemical composition of colostrum is special indicates that its most important function is not necessarily to provide nutrition for the baby, but actually to quickly strengthen the baby’s immune system, digestion, and development. They were in a sterile environment in the womb, and they need this boost before they’re exposed to all the microbes and substances that they’ll have to acclimate to as they spend more time in the world.

After a few days of receiving colostrum, the chemical composition of milk begins to change. When and how it changes exactly depends on a lot of factors. How often is the baby feeding? How well is the baby feeding? Is the baby healthy and growing? Is the mother healthy and getting adequate hydration and nutrition? If all is going well, transitional milk will be made sooner. There will be a lot more milk, and what’s in the milk will be different.

There will be more nutritional value because the baby can better digest it now, and the baby is growing quickly and needs more energy. The milk also continues to have some of the components of colostrum. After several days or even a couple of weeks of this transitional milk, the mature milk begins to develop. The milk will be fully mature by about 4-6 weeks. Again, how quickly this happens depends on the state of the lactating parent and the needs of the baby. The milk production system reads the physiological signs coming from mother and baby and creates the milk that is most needed. Magic!

Nutritional Composition of Milk

The main nutritional components of mature milk are protein, fat, and carbohydrates (lactose). The proportions of these nutrients in the milk varies. It depends some on the mother’s BMI, protein intake, how many babies she’s had, whether she’s started menstruating, and how often she feeds the baby.

It also depends on how much milk she produces. Usually, when there is MORE milk, it is lower in fat and protein but higher in lactose. Someone who makes less milk might have milk that is higher in fat and protein making it more calorie dense so the baby doesn’t need quite as much to get the same amount of nutrition.

The nutritional content of milk also changes depending on the time of day! There is usually less fat overnight and in the morning, and more in the afternoon and evening, adjusting to the needs of an infant.

There are also micronutrients in human milk including vitamins A, B1, B2, B6, B12, D and iodine. A breastfeeding parent might get deficient in some of these micronutrients, so it’s important to continue taking vitamin supplements and eating a healthy diet during lactation so these micronutrients are shared with the baby.

The nutritional composition of human milk can be pretty well duplicated in infant formula. Making sure to have appropriate levels of fat, protein, carbohydrates, vitamins, and minerals is very important and formulas are now doing a good job of this. There are even different formulations depending on the baby’s age, condition, and health so they can get a more customized formula to meet babies’ needs.

Bioactive Components of Milk

The things that have not been possible to duplicate are the bioactive components of human milk. The fats, proteins, carbohydrates, and micronutrients provide the nutrition, but the bioactive components are the medicine.

There are macrophages and stem cells that protect against infection, inflammation, and help the baby’s body recover from injury and illness. There are immunoglobulins which are antibodies designed to fight pathogens that might enter the baby’s body such as bacteria and viruses.

There are also growth factors in human milk. These are hormones which trigger and support the baby’s growth and development. And there are even probiotics which help populate a baby’s sterile and immature digestive system with good bacteria preparing it for digestion and nutrition.

Many of these bioactive components are even designed not so much to provide nutrition for the baby, but for the microbes that are populating the baby’s gut! With a good gut microbiome, a baby is better able to digest food, absorb nutrients, and have a good immune response.

Human milk is alive and active. It is constantly growing and changing and can’t be perfectly duplicated. There is an entire branch of science dedicated to breastfeeding medicine, and they are discovering new components and benefits to breast milk all the time.

It’s also important to note that the mother’s body has the ability to detect changes in the baby through their physical contact and create a new milk formulation to suit that particular baby’s new needs. If a baby is sick or having a lot of sudden growth, the milk can adjust to provide what is most needed.

A baby will receive a lot of benefits from breast milk, especially milk from their own parent, that they can’t get from any other source. It’s also important to remember that some breast milk is better than none, so if you can manage to breastfeed part-time or for a short amount of time, that does a lot of good!

If you’re getting ready to breastfeed, we recommend taking our live online Breastfeeding 101 class. If you’re already breastfeeding and struggling, make an appointment with our lactation consultants for help.