Breast size plays an important role in breastfeeding, which one?

The benefits of breastfeeding are well established. The milk produced by the breastfeeding parent contains everything needed for the healthy development of the baby, even if the composition is never identical. It is difficult to know why it varies from one person to another and from one moment to another because, even if studies have been carried out on the subject, the factors leading to these variations are unknown and poorly understood. New research is looking at breast size: does the composition of milk change according to breast size? It would seem so.

This study, carried out in Wroclaw, Poland, was published in theAmerican Journal of Human Biology in February 2024. The researchers recruited 162 exclusively breastfeeding women between February 2017 and July 2018. The participants were then selected according to certain criteria to ensure a homogeneous sample. Only 137 of them were therefore selected, having given birth at term following a large non-multiple, not suffering from chronic diseases, not using hormonal contraception, having given complete information about themselves and not having an unusual diet.

For each woman, the breast and area under the breast were measured. For them as for the children, the body mass index (BMI) and body fat percentage were recorded. Mothers were asked to complete a questionnaire on their socioeconomic status, reproductive history, and breastfeeding pattern. Finally, they provided samples of their milk, which were collected with a hospital breast pump mid-morning, a time identified as optimal for standardizing milk composition. These samples were analyzed by scientists to quantify their concentration of lactose, fats and proteins.

Difference in milk composition depending on breast size

Contrary to what they expected, the results showed that the composition of milk does change depending on breast size. Thus, participants with larger breasts produced milk containing less lactose, while those with smaller breasts had a higher concentration of lactose in theirs. These results were identical depending on the mother’s adiposity, her nutrient and calorie intake, the frequency of feedings, the size of her infant, her age and even her socio-economic status. In contrast, no significant association between breast size and the concentration of other nutrients, such as fat and protein.

The authors of this study indicate that this finding is particularly interesting because the production of lactose found in human milk occurs only in the mammary glands. To explain this result, they hypothesize a hormonal influence. Indeed, having a large breast is linked to higher levels of estradiol and progesterone, hormones that can decrease overall milk production and inhibit lactose synthesis by reducing levels of the protein alpha-lactalbumin in milk.. “This is the first study to report a negative relationship between lactose concentration in breast milk and maternal breast size during fully established lactation. The demonstrated association indicates that women with larger breasts can, via hormonal control, produce milk with a lower lactose concentration than women with smaller breasts.“the researchers say.

The study also shows that the frequency of feedings also affects the concentration of lactose: when they are more frequent, the milk contains greater quantities of this nutrient. This is probably due to the fact that there is a greater production of prolactin, a hormone stimulating milk production, the researchers indicate. Likewise, mothers who had a higher calorie intake had less lactose in their milk. This could be explained by the impact of glucose on lactose metabolism and synthesis.

Please note, this study does not mean that the milk of breastfeeding parents who do not have small breasts is of poor quality. It simply has a different composition and provides other nutrients to the baby, so this should not be a source of complexity. Likewise, you should not force yourself to achieve a greater frequency of feedings or monitor your diet excessively. You must respect the baby’s rhythm and have a balanced and sufficient diet. In any case, human milk remains the best food for infants and, along with infant milk, it should be the only food given before the age of 4-6 months, the recommended time to start dietary diversification.