The biochemistry behind Breastfeeding

After a person has given birth, one of the first natural maternal instincts is to hold the baby up to their chest so it can do one of the main things required for human survival - to eat. The breast milk produced contains supplements to nourish and give the newborn baby what it needs to survive. However, the body must first find a way to produce and release it. This process is facilitated by the hormones prolactin and oxytocin.

Prolactin is a polypeptide hormone made of 199 amino acids, and is produced by the pituitary gland in the brain. In humans, the prolactin molecule is arranged in a single chain of amino acids, with three intramolecular disulfide bonds between six cysteine residues (another type of amino acid). It starts to be released during the end of pregnancy, but high levels of oestrogen and progesterone counteract its effects. After birth, the levels of oestrogen and progesterone drop rapidly which allows prolactin to stimulate the production of breast milk. This is known as lactogenesis. Prolactin causes the lactocytes (the milk producing cells on the alveoli in the breasts) to take proteins, fats and sugars from the blood supply in order to produce breast milk.

Oxytocin is often known as the ‘love drug’ or the ‘cuddle hormone’ and is associated with empathy, trust, and relationship-building. The levels of oxytocin increase in times of bonding between parent and child such as skin to skin contact, in childbirth, and whilst hugging. It is a protein made of nine amino acids (a nonapeptide) in the sequence: cysteine-tyrosine-isoleucine-glutamine-asparag ine-cysteine-proline-leucine-glycine-amide. Oxytocin is made in neurosecretory cells, in the hypothalamus, and is released into the blood from the pituitary gland. After birth, suckling by the baby is relayed by spinal nerves to the hypothalamus. The stimulation causes neurons to secrete oxytocin in intermittent bursts. This triggers the milk ejection reflex also known as ‘let down’. In this scenario, oxytocin causes the cells around the milk-filled alveoli to contract and squeeze milk out through the milk ducts to allow the baby to feed.

Breastfeeding works on a supply and demand regime through the use of a small whey protein found in breast milk called Feedback Inhibitor of Lactation (FIL). FIL is thought to slow milk synthesis. Therefore, when the breast is full of milk, there is more FIL and less milk is produced. When the breast has less milk, there is less FIL and milk production speeds up.

Whilst the exact chemical profile of breast milk is still unclear, there are a multitude of components we know that are necessary for a baby’s growth and development. Millions of live cells, including white blood cells and stem cells, boost the baby’s immune system and help organs develop and heal. Antibodies from the mother, either through vaccinations or infections, flow directly to the baby and help protect it against illnesses and infections - this is known as passive immunity.

Many hormones (proteins that carry messages to organs and tissues) are vital components of breast milk. Thyroid hormones control the baby’s metabolism, endorphins act as natural painkillers, and leptin controls the baby’s appetite, weight and how much energy it uses. Enzymes will act as catalysts in the baby’s metabolic reactions, such as aiding digestion and absorption of iron. There are also supplementary mineral ions in breast milk such as Na+, K+, Ca2+, Mg2+, and Cl- that support healthy growth and organ function, and help build the baby’s teeth and bones.

Polyunsaturated fatty acids (long hydrocarbon chains that contain a double bond) such as the fats found in vegetable oils, nuts and seeds, are also found in human milk. This fat is characterised by high contents of palmitic and oleic acids. They are used to build the baby’s nervous system and aid in eye development. Free amino acids such as Taurine, glutamic acid, and glutamine also help make up the breast milk, in addition to the amino acids that build proteins such as whey and casein. These will aid growth, activate the immune system, and develop and protect neurons in the brain.

Finally, carbohydrates make up a wide portion of the breast milk as it provides the baby with the energy needed to survive. Most of this is in the form of lactose (a sugar) that provides 40% of the baby’s calories through its breakdown, by the enzyme lactase, into the sugar molecules glucose and galactose in the gut. The other type of carbohydrates are oligosaccharides. These are polymers consisting of a small number of simple sugars that act as probiotics in the gut and help prevent infections. They are the third largest solid component of breast milk and the key differentiator between human and cow milk.

2’ - Fucosyllactose is one of the 150 oligosaccharides found in human milk. It makes up most of the human milk oligosaccharides (HMOs) found in infant formula as it is easy to mass manufacture using fermentation and is safe and effective. HMOs were not used in infant formula until around 2015. Infant formula is largely composed of cow’s milk that has been treated to make it more digestible for babies.

Whilst breastfeeding has an array of benefits, it is not a process that is available or beneficial to many mothers. The increasing popularity and quality of infant formula due to more research on chemical synthesis of products of human milk has led to feeding becoming a much more accessible process for many. Many report that birth and breastfeeding can feel like

a completely daunting, unknown experience, and it can be useful to know the changes and processes happening inside your body in order to provide for another.

By Cassie Wigoder

Sources:

https://medlineplus.gov/lab-tests/prolactin-levels/ https://wicbreastfeeding.fns.usda.gov/how-breast-m ilk-made

https://www.chemistryworld.com/features/the-scien ce-of-breast-milk-and-baby-formula/4014574.article

https://www.medela.com.au/breastfeeding/blog/awe some-breast-milk-facts/how-breastfeeding-actuallyworks-exploring-the-science-of-breast-milk-feeding https://journals.physiology.org/doi/full/10.1152/phys rev.2000.80.4.1523

https://www.worldofmolecules.com/emotions/oxytoc in.htm

https://www.medicalnewstoday.com/articles/275795 https://www.medela.com/breastfeeding/mums-journ ey/breast-milk-composition

https://pubmed.ncbi.nlm.nih.gov/392766/