THIN MILK AND THICK MILK
Q:
I’m reading a lot of conflicting information on the existence of foremilk and hind milk. Does the first milk really quench and the later milk provide nutrition?
A:
Linda says: Studies and research regarding breast milk and lactation are continuous, as we learn more about this very special nutrition designed for babies.
English surgeon and anatomist Sir Astley Cooper published what is known as the standard model of the breast in 1840. His anatomical dissections of the breast is what appeared in textbooks right up to this new millennium. According to these, it was thought that ducts expanded into lactiferous sinuses or reservoirs, which collected and stored large amounts of milk, as a foremilk, in the front of the breast behind the nipple. But in the early 2000s, new research using high-resolution ultrasound imaging examinations and scans of the breast changed our thinking completely. We now know the correct internal anatomical structure of the breast, the way the breast functions during lactation, the physiology of milk production, and also how the baby breastfeeds.
When a baby is well positioned and latched deeply on the breast, a good vacuum is created. The baby stimulates the breast with a quick sucking action to initiate the release of the hormone oxytocin, which causes the alveoli where the milk is made, to contract. This is called the milk-ejection reflex, also known as the “let-down”, and the milk is squeezed out into the ducts and from the breast, through the nipple, into baby’s mouth. A significant amount of milk is transferred, and Baby starts to swallow well with a coordinated rhythm. Very little milk, less than 10ml, can be removed from the breast before the let-down happens. Therefore, a rapid, efficient first milk-ejection reflex is important for optimal milk removal and to stimulate further let-downs throughout the feeding session.
The hormone prolactin, responsible for producing milk, is also released at feeding time, and with each session, more milk is made and stored in the breast alveoli. Measurements of the concentration of some of the components of breast milk help us determine what happens through the feeding session. Gradients in fat concentrations vary according to how full the breast is at the time. The actual fat content of the milk coming from the nipple will depend on the fullness of the breast, which is dependent on the intervals between breastfeeds and how well the breast is drained during the feed. High-fat milk is the last to be expelled from the alveoli where the milk is made, therefore the fat content of the milk increases as the feed progresses related to the number of milk ejections.
The longer the intervals between breastfeeds, the lower the fat content of the milk that first comes from the nipple and the higher the fat content of the milk that comes from the nipple as the letdowns happen, and the alveoli drains. However, breastfed babies have a daily fat intake from both breasts of between 15 and 50g, which is independent of their breastfeeding frequency.
So, it’s now understood that the fuller the breast is at a feed session, the more diluted the fat content will be, and so breast milk differs throughout the day, according to baby’s individual need.