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Breast milk nutrition
Allaitement maternel et alimentation des nouveau-nés
28 juillet 2023

What’s breast milk made of?

What makes breast milk nutritious? Valentina De Pietro, a midwife specializing in lactation, explains more about breastmilk composition. 

Vitamins, minerals, sugars and what else...? Find out by reading the article! 

When and how is breast milk made?

The beginning of lactation is called "lactogenesis" and occurs in three stages.  

The first stage of lactogenesis begins about 12 weeks before the birth, when the mammary glands begin to secrete colostrum.  

Breast size increases at this stage as the alveoli (small sacs inside the mammary glands) fill with colostrum. 

The presence of high levels of the hormone progesterone in the mum’s blood inhibits full milk production until after the birth.  

The second stage of lactogenesis begins after the birth, when the placenta is expelled. Progesterone levels decrease suddenly, while prolactin levels remain high. Prolactin is the main hormone for lactation. 

Two or three days after childbirth your milk comes in and your breasts begin filling up: colostrum changes from transitional to mature breast milk. The amount of milk produced increases rapidly and the composition gradually changes from colostrum to mature milk.  

Since this process is controlled by hormones, breasts begin to produce milk whether a mum is breastfeeding or not.  

At this stage of lactogenesis, it is important to breastfeed often (and/or extract milk manually or with a breast pump if your baby is still learning how to latch on), simply because the more a new mum breastfeeds, the more milk she will produce. If she doesn’t breastfeed frequently, her milk production will decrease. 

The composition of breast milk

For an infant, there is no better nutrition than mum’s breast milk. It contains all the essential substances needed for a baby’s growth and colostrum (the first milk) provides them with protective factors for their future health. 

The calorie content of milk (including fat, sugar and protein) averages 700 calories per litre. 

Here’s what it’s made up of: 


Water makes up 87% of the volume of breast milk. 

It’s used to produce new cells, eliminate waste, and compensate for the abundant losses that occur through urine, sweat, and feces. 


Most of it is synthesized by the mammary gland cells. Blood proteins are also present in small amounts. The composition of human milk protein is such that it is 100% absorbable by the infant's body.

  • Casein, is a large protein rich in phosphorus, calcium and magnesium. 
  • Whey protein 
  • Alpha lactalbumin, is necessary for the absorption of lactose and sugars as well as being essential for brain cell development. 
  • Lactotransferrin, which has the very important function of binding iron and promoting intestinal absorption. Inside the intestine, it leaves the iron necessary for the development of non-pathogenic bacteria contributing to beneficial gut flora, helpful for protecting against infection. Thanks to this protein all the iron contained in breast milk is absorbed and utilised. 
  • Immunoglobulins, also called antibodies, protect the body against infection. Milk is rich in secretory-type immunoglobulin A (Ig As), which adhere to the intestinal mucosa, forming a kind of "enamel" on the intestine that prevents foreign proteins, germs and viruses from passing to the bloodstream.
  • Serum albumin, a human species-specific protein. 
  • Orosomucoid, also specific to the human species. 
  • Proteins related to folic acid, vitamin B12, cortisone, etc. 
  • Free amino acids, simple molecules that are used to build proteins and become part of cells. They are distinguished into nonessential amino acids, which the body is able to produce itself, and essential amino acids, which cannot be synthesized by the body but are essential for its survival and must be supplied by food.  
  • Enzymes, which are essential for the production and destruction of molecules and cells.  
  • Epithelial growth factor, hormone that influences the growth and development of the intestinal tract. 


Milk contains 70 grams per litre of sugars, consisting of 60 grams of lactose and 10 grams of oligosaccharides. 

Lactose increases the absorption of calcium, which is essential for good bone structure and healthy teeth. In the intestines, it promotes the development of lactobacilli, which acidify the intestinal environment, preventing the development of dangerous germs.  

Lactose is broken down into two molecules, glucose, and galactose, by the enzyme lactase, which is present in the foetus from as early as the first few months and peaks at birth.  

Lactase declines with age and, in adults, persists only in European or European-derived populations. Other races, lacking lactase, become milk intolerant.  

Glucose and galactose pass into the bloodstream through the intestinal mucosa and from there into tissues where they perform important functions in brain, muscle, and fat cells, the liver, etc.  

Galactose, in particular, is essential for the production of cerebrosides, the basic components of brain tissue. Brain growth is maximal throughout the first year of life, and no other milk is as rich in lactose as human milk, which contains twice as much as all other animal milks. 

Oligosaccharides are responsible for providing immediate energy and promoting the intestinal development of lactobacilli that protect against gastrointestinal infections. 


The amount of lipids in human breast milk is about 40 grams per litre, but it varies from woman to woman, the time of day, the age of the child, the amount of milk produced…essentially it can range from 3 to 180 grams per litre. 

Fats are 98 percent triglycerides, half unsaturated and half saturated. From some unsaturated fats we derive arachidonic acid (AA), which is very important as it’s necessary for the formation of neurons and prostaglandins, and docosahexaenoic acid (DHA). Higher levels of DHA and AA in the blood are associated with better cognitive and vision development. 

The saturated fatty acids in human milk have a special composition that increases their absorption by the intestines: in fact, curdled milk is soft and light and the baby's stomach empties quickly and easily. Therefore, they want to feed often stimulating the production of more milk. 

Milk triglycerides also transport the fat-soluble vitamins (A, D, E, K) across the intestinal mucosa enabling their absorption. 


Human breast milk contains all the nutrients a baby needs, in ideal proportions. For healthy, full-term-born babies, additional vitamins and mineral supplements are not necessary. If they are needed, breast milk compensates the deficiency. 

Vitamin D, is needed to absorb calcium. How much a baby requires varies depending on the amount they were able to store in their liver during pregnancy; they will need more if mum was deficient, if the baby was born prematurely, or if they are a twin. Supplements are needed only for dark-skinned individuals who live in northern climates or who for various reasons have poor sun exposure. Just 15 minutes a day even in front of a window is sufficient exposure. 

Vitamin K, prevents the occurrence of bleeding. It’s equal to 15 mg per litre. 

Vitamin E, is a powerful antioxidant and protects red blood cells. 

Vitamin C, is needed for iron absorption. It is equal to 43 mg per litre. If mum smokes, the value will be lower. 

Vitamins B6 and B12, are essential for an infant’s development and proper neurological functioning. B12 is present if mum includes foods of animal origin in her diet or supplements if she consumes a plant-based diet such as vegan or macrobiotic. 

Mineral salts 

Milk contains 2 grams per litre of mineral salts. Specifically, about 100-200 mg of sodium and a small amount of chlorine and potassium to reduce strain on the kidneys. 

The benefits of breast milk

Breast milk benefits both baby and mum, as the NHS breastfeeding guidelines explain. 

Scientific research at an international level has shown that breastfeeding: 

  • reduces the incidence and duration of gastroenteritis. 
  • protects against respiratory infections. 
  • reduces the risk of developing allergies. 
  • improves vision and psychomotor development. 
  • improves intestinal development and reduces the risk of occlusions. 
  • contributes to better mouth conformation. 
  • protects against ear infections. 
  • reduces the risk of diabetes and cancers of the lymphatic system. 

These, on the other hand, are the health benefits of breastfeeding for mum : 

  • reduces the risk of developing osteoporosis. 
  • Prevents against some forms of breast and ovarian cancers. 
  • stimulates the natural contraction of the uterus by reducing natural postpartum bleeding and allowing the uterus to return to its normal size more quickly. 
  • Helps mum lose pregnancy weight. 
  • It’s free; there are no preparation costs. 
  • It’s practical: always ready at just the right temperature. 


Valentina De Pietro, Midwife and Lactation Consultant 

A trained healthcare professional, Valentina follows mums throughout their maternity journey from pregnancy to post childbirth, offering guidance and support, by means of prenatal consultations and courses, on breastfeeding and weaning. 

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