Milk fat and hindmilk

What are foremilk and hindmilk?

During breastfeeding, the amount of fat in the milk increases as the breast empties. Milk delivered in the later part of a breastfeed is called hindmilk. Foremilk, delivered at the beginning of the feed, has slightly less fat. Both types of milk are good and concerns about fore- and hindmilk should not direct the feeding pattern. Studies show the amount of fat a baby gets in a day doesn’t depend on whether the baby takes one breast or two.

A) Describing foremilk and hindmilk

Milk fat is the most variable component of breast milk (Ballard 2013). Milk fat content of breast milk changes:

  • Between mothers.
  • As the baby grows.
  • At different times of the day.
  • During each feed.

Fat content in milk is higher during the day and evening and lower during the night and morning (Kent 2006). 

Milk fat content will change during each feed. Foremilk is the milk the baby gets at the start of the feed. It is generally lower in fat. Hindmilk is the milk the baby gets later in the feed and is slightly higher in fat. The terms foremilk and hindmilk simply acknowledge the normal change in milk fat; they are not different types of milk. The emptier the breast, the higher the milk fat (Daly 1993).

These changes are also seen when expressing.

Hindmilk has slightly more calories and vitamins A and E than foremilk but the same amount of protein (Nielsen 2017).

B) The formation of foremilk and hindmilk

Milk is made and stored in the milk sacs (alveoli) within the breast. Each of the millions of alveoli is surrounded by muscular cells that contract when the level of the hormone oxytocin rises during the let-down. This squeezes the milk out of the sacs, into the milk ducts, and towards the nipple.

Milk fat is organized into tiny balls (globules) that are lightly attached to the inner wall of the alveoli. It is thought that during the let-down, the centres of the alveoli empty first and send milk with fewer fat globules down the milk ducts and toward the nipple. As the squeezing continues, the fat globules are released. They then leave the inner wall of the alveoli and join the milk moving toward the baby, increasing the amount of fat (Atwood 1992; Masedunskas 2017).

C) The importance of milk fat

Milk fat provides 50% energy in breastmilk. While mothers may worry about fore- and hindmilk issues, the quality of milk is rarely the cause of poor growth. Rather it is the lack of breast milk or illness of the baby that are the most common causes.

Some mothers are told to adopt certain feeding patterns such as using only one breast per feed so that the baby can “get the hindmilk”. This is not appropriate. The amount of breast milk fat intake of a baby over a whole day does not depend on (Kent 2006):

  • The number of breastfeeds per day.
  • The baby’s age (Mitoulas 2003).
  • The baby’s sex.
  • Whether the baby generally takes one breast or two.
  • Whether or not the baby breastfeeds during the night.

A mother should simply follow her baby’s hunger signs for feeds, offer the second side if the baby is hungry after the first, and ensure the baby is taking in enough milk

References

Atwood CS, Hartmann PE. Collection of fore and hind milk from the sow and the changes in milk composition during suckling. J Dairy Res. 1992 Aug;59(3):287-98

Ballard O, Morrow AL. Human milk composition: nutrients and bioactive factors. Pediatr Clin North Am. 2013;60(1):49-74
 
Daly SE, Di Rosso A, Owens RA, et al. Degree of breast emptying explains changes in the fat content, but not fatty acid composition, of human milk. Experimental Physiology 1993; 78; 741-755
 
Kent JC, Mitoulas LR, Cregan MD, et al. Volume and frequency of breastfeedings and fat content of breast milk throughout the day. Pediatrics. 2006 Mar;117(3):e387-95

Masedunskas A, Chen Y, Stussman R, et al. Kinetics of milk lipid droplet transport, growth, and secretion revealed by intravital imaging: lipid droplet release is intermittently stimulated by oxytocin. Mol Biol Cell. 2017 Apr 1;28(7):935-946

Mitoulas LR, Gurrin LC, Doherty DA, et al. Infant intake of fatty acids from human milk over the first year of lactation. Br J Nutr. 2003 Nov;90(5):979-86
 
Nielsen SD, Beverly RL, Dallas DC. Peptides Released from Foremilk and Hindmilk Proteins by Breast Milk Proteases Are Highly Similar. Front Nutr. 2017 Nov 2;4:54