This blog post discusses "Fat structure and composition in human milk and infant formulas: Implications in infant health", a peer-reviewed journal article published in Clinical Epidemiology and Global Health on Science Direct.
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Infant formulas: When breastfeeding is not recommended
Exclusive breastfeeding is the optimal recommendation for infants 0 to 6 months due to its superior nutritional quality and protective factors [1]. However, there are cases when breastfeeding is contraindicated, i.e. when the infant has a genetic disorder, e.g. galactosemia, which requires specialized formula milk to avoid any adverse reactions associated with intolerance of breast milk components, or when the mother is infected with a disease [2]. In these cases, even nutritionist-dietitians have no choice but to recommend formula milk for these infants.
Human milk and formula milk: Differences in fat structure
Stereospecific positions of fatty acids [3]Manufacturers designed formula milk to mimic the composition of breast milk, which is rich in palmitic acid, without knowing that fat structure is different for both milk types. Palmitic acid found in breast milk is esterified at the sn-2 position, while the one found in formula milk is esterified at the sn-1 and sn-3 positions.
Adverse effects of formula milk
It was found that formula milks are associated with adverse effects such as allergies, constipation, and decreased calcium and fat absorption. This is due to the release of free palmitic acid at the sn-1 and sn-3 positions upon digestion by pancreatic lipase. Free palmitic acid, when combined with free calcium, forms insoluble soap, which prevents fats and calcium from being absorbed and passing harder stools.
On the other hand, the palmitic acid found in human milk is well-absorbed. It is left unhydrolyzed by pancreatic lipase, leaving it as an sn-2 monoglyceride that is absorbed via passive diffusion. Hence no insoluble soaps are formed with free calcium and magnesium, and the risk of constipation is reduced.
Many studies have explored ways to address this problem, particularly constipation and decreased calcium and fat absorption. This study is one of them, whilst being the most recent among those studies.
Prior research has found that the long chain saturated fatty acids (LCSFAs) esterified at the sn-1 and sn-3 positions found in formula milks, as opposed to fatty acids (FA) esterified at the sn-2 position in breast milk, contribute to the aforementioned problems. Thus, the authors hypothesized that reducing palmitic acid, an LCSFA, would be the solution.
Research methods and summary of results
The study conducted randomized controlled trials to examine the effects of formula milks on stool consistency, and absorption and excretion of calcium and fat.
The bottomline results are:
- Calcium and fat absorption was significantly higher in formula milks with lower LCSFA levels.
- Formula milks with low content of LCSFAs lead to softer stools
- Calcium excretion was lower in formula milks with lower LCSFA levels.
- Calcium and fat excretion was lower significantly lower in formula milks with lower LCSFA levels.
Therefore, infants fed formula milks with lower LCSFA levels are less likely to experience constipation, absorb more and excrete less calcium and fat.
All p-values are significantly lower than the 0.05 cut-off, suggesting that these results are significant.
Conclusion
The study found that reducing the LCSFA levels of formula milks associated with the release of free palmitic acids and formation of insouble soaps with free calcium leads to greater absorption and less excretion of calcium and fat, and thus reduced constipation.
Although the study did not explain the methodology in detail, their research is valuable based on the study design and interpretation of results. Also, the results match those of the other studies, and they logically follow the premise stated initially.
It would be useful in clinical practice, as nutritionist-dietitians would be informed about formula milks that are more suitable to infants who cannot be breastfed. It gives a valid option to mothers who want to give their children appropriate and safer milk other than breast milk, in cases when the child cannot consume it.
References:
[1] http://www.who.int/nutrition/publications/IYCF_Participants_Manual.pdf
[2] https://www.cdc.gov/breastfeeding/breastfeeding-special-circumstances/contraindications-to-breastfeeding.html
[3] https://www.sciencedirect.com/science/article/pii/S221339841830037X