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Composition of breast milk

Composition of breast milk


Did you know that the nutrient composition of your breast milk changes throughout each feed every time you breastfeed? I find the human body truly amazing and I hope that this blog will help you understand why formula will NEVER come close to replacing breast milk.

You may or may not have heard of the terms “foremilk” and “hindmilk” (examples are pictured) but these are terms used to describe breast milk. As the names suggest, the foremilk comes first, and then over the course of breastfeeding, the breast milk begins to change in composition to eventually become hindmilk. It looks something like this…

All this is great but what does it mean?

Over the course of a feed the amount of fat in the breast milk increases so let’s have a look at what happens WITHIN the breast. You would think it is all just mixed up together so why does the composition of the milk change from having a higher water content to having a higher fat content?

When breast milk is produced, the body only makes one type of milk which is mainly made up of water, fat, carbohydrates and proteins. The fat within the breast milk is quite sticky and forms fat globules that stick together in the milk ducts of the breasts.

As more milk is produced, the heavier, more watery milk moves toward the nipple, leaving the fat globules stuck together higher up in the milk ducts. As the milk ducts dilate and the baby begins to breastfeed, the more watery milk is released. As breastfeeding continues and the breast empties, the fat globules begin to breakdown and the milk becomes less watery and more energy rich. The further on in the feed, the more the fat content of the milk increases as you can see by this table below.

Changing composition of breast milkA sample of breast milk composition when 12 samples were taken at approximately equal intervals during breastfeeding.

It may be easier to visualise the results it the following graph.

Changing fat and water content of breast milkYou will see that the blue protein line and red carbohydrate line remain consistent. However if you focus on the green fat line you will notice that it rises as the purple water line drops. So you can see the fat content of the milk increases over time. So the initial period of breastfeeding is ensuring that the baby receives adequate fluids to avoid dehydration. As breastfeeding continues the composition of the breastmilk changes to provide more fat for the babies growth.

These results may vary depending what time of day it is and how long between each time you breastfeed. Research suggests that the fuller the breast, the higher the water content of the milk and the greater difference between the amount of water at the beginning of the feed to the end of the feed. An emptier breast may have a higher fat content throughout and therefore less change in water content between the beginning and the end of breastfeeding. The results will also certainly vary from mother to mother.

You may notice that if you express and leave the expressed milk in the fridge overnight it separates. The fat within the milk is lighter than the rest of the milk and so it separates out over time. This is why when expressing milk you should try to express an entire breast full of milk to ensure the milk is complete.  When you want to use the express breast milk, you just need to give it a good shake. This is similar to the way cows’ milk is “homogonised” to ensure the fat content remains consistent throughout the milk.

 Taking away from this what do you really need to know:

  • Firstly, babies all have their own breastfeeding patterns, they breastfeed for varying lengths of time and at different intervals. But they are usually capable of giving you enough information (via screaming and not sleeping!) to ensure they maintain a healthy body weight.
  • We really don’t need to be too concerned with the composition of our breast milk. Our bodies are pretty good at making sure your baby gets what she needs.
  • As long as you are taking care of your own nutrition, breastfeeding on demand, and allow her to end the breastfeed when she’s finished, you really don’t need to be concerned with too much more.

Written by Helen La Fontaine
Founder – Top Secret Maternity
Bachelor of Applied Science – Food Science and Nutrition | Master of Public Health

 
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