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  • Dr. Kathryn Hopperton

What's in human milk?: Exploring Fatty Acid Concentrations in Human Milk Fed to VLBW Infants

Updated: Apr 13, 2022

A picture of human milk

We know that human milk is the best source of nutrition for all infants. Interestingly, the composition of human milk, the amounts of nutrients and the bioactive components, are unique to every nursing parent. For example, fat and fatty acids (e.g. omega 3s) support infant brain growth but are the most variable macronutrient in human milk. Infants born at a very low birth weight (VLBW) are vulnerable to deficits in fatty acids (FAs) because they are born early and during a period of rapid in utero growth. Thus, it is important that infants born VLBW receive appropriate amounts of fatty acids in their feeds. However, little is known about the factors that influence the fatty acid intakes or composition of their human milk feeds.

In work led by postdoctoral fellow Dr. Kathryn Hopperton, we explored some of the sources of this variability in milk fed to infants born VLBW.


You can read the full study published in the American Journal of Clinical Nutrition here:


What did we find?

The energy in human milk comes from carbohydrates, protein and fat. Fat consists of fatty acids, including saturated, monounsaturated, and polyunsaturated fatty acids (like omega-3 DHA and omega-6 ARA). We measured fatty acid levels in over 450 human milk samples fed to VLBW infants enrolled in the OptiMoM Fortifier Study. We found that the fatty acid concentrations in human milk varied depending on characteristics such as lactating parent’s ethnicity and body mass index (BMI), and to a lesser extent, income and pregnancy length.

What does this mean?

Our work shows that human milk is not a homogenous liquid. Its nutritional content is variable, and this variability can translate into differences in the nutrient intake of infants. Our results do not necessarily mean lactating parents need to take any action. Instead, our results are helpful to health care professionals and researchers. In research and clinical settings, we calculate the nutrient intakes of vulnerable infants to ensure their feeds meet their high nutrition needs to optimize growth. Historically, these calculations use reference values for human milk, which assumes a uniform nutrient composition across all nursing parents. Therefore, estimates based on reference values may lead to an over-or under-estimation of infant nutrient intakes.

What’s next?

The feeds provided to VLBW infants are nutrient fortified in the hospital to optimize growth and development. However, the current standard of care uses a reference value for the nutrient content of human milk to calculate how much fortifier to add to human milk feeds. Our group recently began a clinical trial, called INFORM, to test a new way of fortifying the feeds of VLBW infants while in the hospital. This new way of fortifying is called individual fortification. It uses measurements of human milk nutrient composition rather than estimates based on reference values. Individual fortification may lead to improvements in the nutritional support of infants born VLBW.

To learn more about the INFORM trial, check out the research section of our website here:


This research was supported by the Canadian Institutes of Health Research (CIHR). Dr. Hopperton was also supported by a CIHR Postdoctoral Fellowship.


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