Breast Milk and How It Varies

Breast Milk and How It Varies

Breast milk is well known as a super-substance and is arguably the only real ‘super food’. It provides infants with optimal nutrition, tailored hydration and protective factors.  Part of breast milk’s brilliance is its ever-changing nature which depends on many factors.

Think about the variations between our adult diets; what dictates these? Where we live, our ethnicity, weather, time of day, time of year, etc. All of these external factors affect the content of breast milk. i.e. nutrient concentrations, levels of hormones and water content. Internal influences such as mum’s hydration levels, diet and nutritional stores also have an impact on breast milk composition.

Breast milk changes over time and follows a kind of ‘breast milk timeline’:

Breast Milk and How It Varies

Current Available Research

The current available research on breast milk composition shows the following external factors can influence breast milk composition:

  • When baby is born: The make-up of breast milk is slightly different when a baby is born pre-term. Specifically, protein levels are reportedly higher when compared to milk from mums whose babies were born at term or after. This difference regulates itself after a couple of months.
  • Over the day: The concentrations of breast milk nutrients (particularly lactose, fat and protein) vary depending on time of day. Hormone concentrations in milk also fluctuate over 24 hours. These changes are thought to be due to natural hormonal rhythms and/or maternal diet and eating patterns. Although, we currently can’t say for sure why these variations occur.
  • Over the feed: The initial milk a baby receives is called ‘fore milk’. Which contains a lot of water and therefore lower concentrations of nutritional components such as fat and protein (lactose levels remain high). As a baby feeds from the breast they drain or ‘empty’ the breast.  The fat content gradually increases, resulting in a fattier and consequently more calorific milk known as ‘hind milk’.  The more volume drained from the breast the higher the fat concentration becomes. Therefore, longer feeds tend to leave babies feeling fuller due to the combined effect of having consumed larger volumes and more calorie dense milk.
  • Over the year: Breast milk changes as babies grow in order to meet their changing nutritional demands.  Protein concentrations decrease gradually over the course of the first year of life.  Energy and fat levels increase from birth to around 1 month, then slowly taper off again until the end of the first year.  Lactose levels increase initially as milk matures and remain the most static of all the macronutrients in milk.  These variations have been observed in multiple studies on milk from many women. However, the reasons for these fluctuations are not yet fully understood but are likely linked to babies changing needs as they grow.

Women’s bodies are programmed to ensure adequate levels of nutrition in their milk, even when the woman’s own nutrition is lacking.  This means that despite all of these influencing factors, breast milk will always supply babies with what they need to grow and thrive.


Thank you to Ellen Ward (PhD Candidate researching breast milk and maternal diet and a Breastfeeding Support Worker) for writing this blog.

Breast Milk and How It Varies

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