Feedback Inhibitor of Lactation, or FIL for short, is a substance thought to be contained within breast milk. It knows when your breasts are full or have recently been emptied and helps to regulate the amount of milk you make.

Understanding the Supply and Demand of Breast Milk

If your baby is feeding regularly and draining the milk well, then FIL keeps sending messages to the cells to “fill” the breast with milk again. This is a process known as supply and demand. So, when the breasts are emptied regularly the breastmilk is refilled regularly.

What Happens When Feeding Frequency Decreases?

FIL also plays a role when the breast is not emptied frequently enough. If you or your baby no longer feed regularly, the breast is not being emptied as often as before.

As the breast gets fuller and fuller of milk which you are no longer feeding to baby, FIL sends messages to eventually reduce and then stop the cells from making more milk. After a few days this “feed” will disappear and your milk supply will have reduced.

This is a clever protection method to prevent your milk cells from getting damaged by being too full, but, it also results in reducing milk supply.

This is essentially how weaning works. If you keep reducing the number of feeds then your body keeps reducing the milk supply it makes available in the breasts. This is supply and demand too; reduced demand for the milk leads to less milk supply.

If a mum has mistakenly reduced her milk supply by taking out a usual breastfeed or by introducing a formula bottle feed, she can still increase her milk supply back again.

By reintroducing the breastfeed or expression she originally took out and increasing “demand” to the breasts again, she will notice that within a few days of feeding more frequently the body will be supplying more milk. Supply and demand is simple when you understand it!

The Breasts Work Independently

For example, if for some reason a baby started to only breastfeed on the left breast and stopped feeding off of the right breast, then there would be no demand for milk from the right breast. The FIL would then shut down the milk making cells in the right breast.

As the “demand” was still regular in the left breast it would continue making milk in the left breast. This is how some women can fully breastfeed from just one side.

How wonderful are our clever, energy saving and genius breasts!

Do you have any questions about the “supply and demand” of breast milk production? How would you describe your breastfeeding experience? For more useful tips and conversation check out our Medela Australia Facebook page.

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