How does breast milk benefit your child?

The composition of breast milk changes and adapts to your baby’s needs

Beneficios de la leche materna

Breastfeeding provides unparalleled benefits to the new-born and the mother. Breast milk provides the baby with nutrients that formula will never provide. And its composition changes to adapt to your baby's nutritional needs.

In the 21st century, despite significant improvements in the composition of formula, human milk provides an ideal and complete food for the new-born baby during the first 6 months of life. It is also an important source of milk in the first two years of life, if supplemented with other foods.

The main professional associations, such as the World Health Organization (WHO), the American Academy of Paediatrics (APP), the American College of Obstetricians and Gynaecologists (ACOG), the Spanish Association of Paediatrics (AEP) and the World Health Organization (WHO), among others, recommend breastfeeding as a source of nutrition for infants because of the benefits for nutrition, for the baby’s gastrointestinal system, immune system (the baby’s defences) and psychosocial well-being, as it creates a bond with the mother. This is because it is a balanced food, which contains all the nutrients necessary for the proper development of the new-born baby, in addition to providing important benefits to the mother.

Your milk changes as the baby grows

    Your milk changes with your baby. Depending on the baby's stage of maturity, breast milk undergoes a series of adaptive changes, with different types of milk: preterm milk, colostrum, transitional milk and mature milk.

    • Preterm milk: this type of milk has a different composition over a long period of time and it is higher in protein and lower in lactose than mature milk, as premature new- borns require more protein, lactoferrin and immunoglobulin A, which are also more abundant in this type of milk. In very low birth weight premature babies (less than 1,500 grams), preterm milk may not be sufficient to meet the necessary calcium and phosphorus and sometimes protein requirements, so it sometimes needs to be supplemented.

    Bebé amamantando

    • Colostrum: this is produced during the first 3 to 4 days after birth. It is a thick, yellowish liquid. The volume is 2 to 20 ml, sufficient to meet the needs of the new-born. Colostrum has 2 g/100 ml of fat, 4 g/100 ml of lactose and 2 g/100 ml of protein. It produces 67 kcal/100 ml. It contains less lactose, fat and water-soluble vitamins than mature milk, and contains more protein and fat-soluble vitamins (E, A, K), carotenes (which gives it its yellowish colour) and some minerals such as sodium (which gives it a slightly salty taste) and zinc. Colostrum contains very high levels of immunoglobulin A and lactoferrin, which are subsequently diluted by milk production, when milk volume increases, but remain in the milk. This provides the new-born baby with efficient protection against environmental germs. Colostrum helps the new-born to eliminate meconium (its first stools), produce lactobacilli and immunoglobulins which defend the digestive tract against bacteria, viruses and parasites. It also has an antioxidant action, protecting the new-born from haemorrhagic diseases.
    • Transitional milk: this is the milk produced between the 4th and 15th day of postpartum. Between the 4th and 6th day there is a sharp increase in milk production, known as the milk surge, which continues to increase until it reaches a significant volume (approximately 600 to 800 ml/day) between the 8th and 15th day of postpartum.
    • Mature breast milk: this retains a wide variety of components such as water, proteins, carbohydrates, fats, minerals and vitamins. All this corresponds to the needs of the children in their development.
    • During weaning, milk composition changes and goes through a stage similar to the colostrum, as breasts are not emptied as often.


    Contraindications to breastfeeding

    There are few situations where breastfeeding is contraindicated, and they are very specific depending on the mother or child.

    Maternal causes

    • Infectious diseases of the HIV type, lesions caused by active herpes on the chest to prevent direct contact with them, lymphotropic virus type I and II of T cells, untreated brucellosis, active tuberculosis among others, as well as abuse of toxic substances (alcohol and other drugs).
    • Treatment with medication: if this is the case, the potential risk for the new-born baby should be looked at individually, following the existing guidelines.
    • The mother’s diet is also important. A poor diet is not a contraindication for breastfeeding, although adequate nutrition is desirable. It is recommended that breastfeeding women take vitamin and mineral supplements to meet sufficient breastfeeding requirements.
    • Being pregnant is not an absolute contraindication for breastfeeding. However, fluid and calorie intake should be increased significantly to provide both gestational weight gain and an adequate nutrition for the breastfed child. During pregnancy, milk supply is slightly reduced and changes in composition occur. In high-risk pregnancies, the gynaecologist should advise the woman what to do, as breastfeeding can trigger contractions.
    • Breast abnormalities: prenatal breast examination should include an evaluation of factors that may interfere with successful breastfeeding, such as hypoplastic breast tissue (tubular or flat breasts), which is characterised by insufficient development of the mammary gland, and which will produce little or no milk. Nipple abnormalities and previous breast surgery do not always cause difficulties with breastfeeding, and in most cases this cannot be predicted in advance.

    In new-borns

    • Galactosemia (a hereditary disease) in the new-born is an absolute contraindication, as babies with this disorder cannot use galactose, a component of human milk.

    Benefits for the mother

    As we have seen above, breastfeeding provides a number of benefits to the baby (nutrition, gastrointestinal, immune and psychological well-being) and to the mother, who may also benefit from longer periods of breastfeeding (> 6 months). The mother is protected from diseases related to depression, bone deterioration and it seems that from certain cancers as well, including some subtypes of breast cancer (not all studies are conclusive), especially in women who breastfeed for more than 1 year.​​​​

    Breast pain

    If there is breast pain, which is the most frequent symptom that can appear when breastfeeding, it is essential to observe how the mother breastfeeds the baby, because in most cases the pain is due to an incorrect breastfeeding technique. It is the job of breastfeeding specialists to advise, inform and educate mothers in order to achieve satisfactory and effective breastfeeding.

    It is important for women to be informed and to have pre- and post-natal knowledge of the benefits of breastfeeding before they start in order to sustain lactation for a long enough period, and to be able to make an informed decision about it, so that breastfeeding is more effective and sustained.



    Dr Juana Mª Brenes Sánchez and Dr Nuria Izquierdo Méndez
    Gynaecology and Obstetrics Specialists of the Breast Pathology Unit. Obstetrics Unit of the Hospital Clínico San Carlos (Madrid)