Does what I eat really affect my milk?

Nutrition in breastfeeding

I am a family physician, educator, and mother of two that breastfed both of her children. It was only when I was at work trying to juggle the challenges of a full time practice, being on call and worry over my daughter not gaining enough weight despite drinking enough volume of breast milk that I started to ask myself what is in MY milk.

The idea of women wanting to know what is in their milk is not new. In 1978 a new method was published called a creamatocrit. This was a rough way of extracting how much fat was in a breast milk sample based on the size of the fatty layer of milk after it was spun down in a centrifuge machine. The number of calories was then calculated from the size of the fatty layer.

Not everyone is able or chooses to breastfeed. But if you do it’s helpful to note certain vitamins and minerals in your milk are directly associated with what you eat and the supplements that you take. Numerous studies reveal that breast milk can differ significantly from mother to mother but that term milk within the same mother does not vary as much as we previously thought. Folks used to differentiate between foremilk and hindmilk noting the increased fat content at the end of a feed, however studies found that it does not vary more than roughly 5% from the beginning to the end of a feed. Most physicians would agree it is the volume of milk intake that is correlated with growth.

Each day I am asked by new moms about what supplements they should take now that they are nursing, and if what they eat affects the quality of their milk. Specifically, many women wonder do diet and supplements matter? Does what a women eats actually change the levels of nutrients in her milk? The answer: it does.

Many studies have looked at maternal status and breast milk concentration of nutrients and minerals. The most studied are essential fatty acids. They are called “essential” since our body doesn't make them so we need to consume them. DHA (docosahexanoic acid) has received a lot of attention as it has been shown to be very important for brain growth and neurodevelopment. Other omega-3’s and omega-6 fatty acids are positively correlated to mother’s levels.

For a study in South Dakota, nursing moms were taught about how their diet affects their milk. After the appropriate dietary changes were made they were able to increase their levels in a matter of weeks. The main dietary sources of omega-3 fatty acids are from fish. Due to mercury concerns it is recommended to eat no more than 2-3 meals per week. It should also be noted that there are certain types of fish that should be avoided all together when nursing (e.g., swordfish, mackerel and some tuna).

Not every vitamin and mineral will change over time. Minerals such as sodium, phosphorus, and zinc tend to be consistent across women and over periods of time. Some studies have found a link between maternal calcium and iron and the levels in their milk while others have not. It is difficult to fully understand the relationship as the many studies carried out to date have involved small sample sizes and vary in the methods used to measure these elements.