Similarity index for the fat Fraction between breast milk and infant formulas

This summary is adapted from ‘Similarity Index for the Fat Fraction between Breast Milk and Infant Formulas’ by Hokkanen et al. 2022

Infants receive approximately 50% of their energy from fat present in breast milk or infant formula1. The fat content of human breast milk is very complex, with hundreds of different types of fat to provide the infant with the appropriate nutritional value. In addition to providing energy, these fats have important roles in brain development, gut health, and immune function2. Infant formulas usually use a mixture of fats from different sources in an attempt to replicate the composition found in breast milk. Cow’s milk has several fat components which are similar to that of breast milk, such as milk fat globule membrane. However, it still requires the addition of vegetable oils to meet requirements. Vegetable oils provide linoleic acids which are necessary for development, yet they still do not accurately recapitulate the composition of human breast milk, for example they do not contain cholesterol which has a number of important functions for the infant. For this reason, there are often at least six types of minor fats regularly added to infant formula to meet the requirements for appropriate development.

There are also differences due to the way infant formula is processed. Breast milk is consumed instantly, whereas infant formula must be heat-treated and homogonised to ensure safety. This can alter the fat fraction of the infant formula, impairing its digestion in the infant.

A similarity index for infant formulas and breast milk was developed as a tool to evaluate the chemical composition of infant formulas3. However, there was uncertainty about the indices used for the minor fat components, which are still vital for infant health. In this study, the authors aimed to calculate the similarity index for the fat composition of selected infant formulas on the Finnish Market and the breast milk of Finnish donors. The formulas were selected with the aim of maximum diversity of added fats, with three cow’s milk-based formulas with added vegetable oils and three formulas containing vegetable oils as the main fat source. The fat components of breast milk vary in response to the mother’s diet, the composition varies between individuals and in different geographical areas. This study therefore only provides the similarity index for the infant formulas to Finnish breast milk and may not get the same results as breast milk from another area.

The similarity index for total fat amount (not the individual types of fat present) was high for all the infant formulas. This was attributed to the overall fat content being a simple parameter to adjust in product development, therefore all formulas could easily be adjusted to the required levels by the manufacturer. The cow’s milk-based formulas had higher similarity indexes to the Finnish breast milk samples on average compared to the vegetable oil-based formulas for 3 of the specific fat types measured. However, one of these three fats measured is much higher in breast milk from other cohorts4,5 and therefore may have a higher similarity index to vegetable oil-based formulas in other studies.

The similarity index for the composition of total fats was highest in a cow’s cream-based formula with added sunflower oil, rapeseed oil, coconut oil and fish oil. The lowest similarity index was obtained in a vegetable oil-based formula with sunflower oil, rapeseed oil and fish oil. Again, the cow’s milk-based formulas had higher similarity indexes than the vegetable oil-based formulas.

The individual similarity indexes calculated for a wide range of fat elements were averaged for each infant formula to give an average similarity index. The highest total similarity index was found for a cow’s milk cream-based formula with added fat sources of sunflower oil, rapeseed oil, coconut oil and fish oil and emulsifiers soy lecithin and mono-/di-glycerides. The two other cow’s milk-based formulas had the second and third highest similarity indexes. The threevegetable oil-based formulas had lower average similarity indexes.

From these results it was concluded that using cow’s milk as the primary fat source brings the fat components of the infant formulas closer to that of breast milk than formulas using vegetable oils.

Specific benefits noted were composition of membrane fats including cholesterol, which were not adequately replicated in the vegetable oil formulas. However, to fulfil all nutritional requirements, fat should be obtained from multiple sources. Fish or algae oil was also seen to be effective in this study for providing docosahexanoic acid (DHA), which supports neurodevelopment in infants. A lot of these individual parameters are not controlled by legislation, but still play important roles in infant health and contribute to overall similarity.

Studies such as these are inherently limited by the fact that there are no standard values for levels of fat in breast milk, and as previously mentioned this study remains a comparison to Finnish breast milk only. The similarity indexes may differ in different populations. This study also did not measure every known fat present in breast milk, and it did not include fat-soluble vitamins. It would be impossible to class an infant formula’s fat fraction as identical to that of breast milk, due to the complex nature of these molecules and the likely presence of fats which have not been detected and studied as of yet. Therefore, in conclusion, cow’s milk-based formulas appear to have more similar fat fractions than vegetable oil-based formulas, but breast milk remains the superior option.


  1. Manson, W. G.; Weaver, L. T. Fat digestion in the neonate. Arch. Dis. Child. 1997, 76, F206– F211,  DOI: 10.1136/fn.76.3.f206
  2. Gurnida, D. A.; Rowan, A. M.; Idjradinata, P.; Muchtadi, D.; Sekarwana, N. Association of complex lipids containing gangliosides with cognitive development of 6-month-old infants. Early Hum. Dev. 2012, 88, 595– 601,  DOI: 10.1016/j.earlhumdev.2012.01.003
  3. Al-Abdi, S.; Al-Abdi, J.; Al-Aamri, M. Similarity Index Between Breast Milk and Infant Formula. EC Paediatrics 2017, 64, 91– 111
  4. Kumar, H.; du Toit, E.; Kulkarni, A.; Aakko, J.; Linderborg, K. M.; Zhang, Y.; Nicol, M. P.; Isolauri, E.; Yang, B.; Collado, M. C.; Salminen, S. Distinct Patterns in Human Milk Microbiota and Fatty Acid Profiles Across Specific Geographic Locations. Front. Microbiol.2016, 7, 1619,  DOI: 10.3389/fmicb.2016.01619
  5. Fabritius, M.; Linderborg, K. M.; Tarvainen, M.; Kalpio, M.; Zhang, Y.; Yang, B. Direct inlet negative ion chemical ionization tandem mass spectrometric analysis of triacylglycerol regioisomers in human milk and infant formulas. Food Chem. 2020, 328, 126991,  DOI: 10.1016/j.foodchem.2020.126991
Similarity index for the fat Fraction between breast milk and infant formulas

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