Summary: Effect of milk fat-based infant formulae on stool fatty acid soaps and calcium excretion in healthy term infants

This summary has been adapted from "Effect of milk fat-based infant formulae on stool fatty acid soaps and calcium excretion in healthy term infants: two double-blind randomised cross-over trials, BMC Nutrition (2020)" The primary energy source in an infant’s diet comes from lipids. The fat in human breast milk accounts for 50% of the energy needs for an infant in the first several months of life (1,2) . Human breast milk has a high concentration of triacylglycerols (TAGs), a glycerol backbone composed of three fatty acids. Of the fatty acids present, palmitic acid (PA) plays an essential role delivering almost 10% of the aforementioned 50% energy needs (1). When examining TAGs there are 3 possible positions for fatty acid placement named sn-1, sn-2 and sn-3. The glycerol backbone positions are visualised in the biomolecule shown in Figure 1. In most mammalian breast milk, palmitic acid is located in the sn-2 position of a TAG(1, 2,5). Figure 1. A triglyceride with labeled (sn)-X backbone positions of fatty acids. Andreas NJ, Kampmann B, Mehring L-DK. Human breast milk: a review on its composition and bioactivity. Early Hum Dev. 2015;91(11):629–35. https:// doi.org/10.1016/j.earlhumdev.2015.08.013.[/caption] Currently most infant formulas are mostly composed of vegetable oils as the primary source of fat. Palmitic acid is relatively sparse in vegetable oil TAG content with the exception of palm oil. Palm oil is often included in vegetable oil blends in order to provide infant formulas with the needed palmitic acid content. In palm oil the palmitic acid is bound to TAGs at the sn-1 and sn-3 positions (7). When TAGs are broken down in the human gut, a mixture of enzymes from the pancreas cleave the acids in the sn-1 and sn-3 positions liberating their free fatty acid form. This becomes problematic when digesting palm oil as the free form of palmitic acid is not readily absorbed by the gut and can cross react with free calcium ions to form hard soaps particles in the infant intestines (5,6). Bovine milk fat has a larger amount of sn-2 palmitic acid compared to palm oil, making it closer in chemical structure to human breast milk. This study focuses on the possible beneficial implications of using bovine milk fat based formula instead of vegetable oil based formula on infant health by evaluating the soaps in the stool of infants (6). The study was designed as two double-blind, randomised cross-over trials (CS1 and CS2) conducted simultaneously with full term infants that met certain health criteria. In the CS1 (n = 16) trial, there was a run-in period of 2 weeks where all infants were given vegetable oil based formula. In the following two weeks (period I), the infants were split into two groups with half being given a 50% milk fat formula and the other half being kept on exclusive vegetable oil formula. After period I the infant groups were crossed over to receive the other formula for another two weeks (period II). In the CS2 trial (n = 17), the procedure was to use formula with 20% milk fat instead of 50% milk fat (19.7% and 39% sn-2 located palmitic acid, respectively). Stools samples were collected by the parents of the infants which were assessed based on the consistency, colour, and amount according to the Amsterdam Infant Stool Scale (AISS). The fatty acids, fatty acid soaps and calcium content of the infant stool samples were analysed (8). When comparing the concentration of major fatty acids in the infant stool samples from CS1 and CS2, there was not a notable difference in the amount of palmitic acid and free free fatty acids in milk fat or vegetable oil based formulas. The milk fat based formula groups did have lower concentrations of lauric acid (C12:0) but higher concentrations of myristic (C14:0) and stearic (C18:0) compared to vegetable oil based formula groups. There was a lower level of fatty acid soaps in stool in the milk fat group than the vegetable oil group. Both 50% milk fat and 20% milk fat groups had lower stool calcium concentrations. In CS1 the 50% milk fat group reported watery and soft stools. The vegetable oil group stool consistency was reported as being soft. CS2 20% milk fat and vegetable oil groups reported the stool as soft (8). Effect of milk fat-based infant formulae on stool fatty acid soaps and calcium excretion in healthy term infants: two double-blind
randomised cross-over trials[/caption] The effect of bovine milk-based formula on infant stool fatty acids, fatty acid soaps and calcium is still being studied as it is not yet clearly defined. However, observations have shown that 50% milk fat and 20 % milk fat formula has beneficial effects on the palmitic acid soaps, calcium excretion and total fatty acids in soaps compared to vegetable oil based formulas. In line with previously published research, a higher sn-2 palmitate content in infant formulas, as in the 50% milk fat formula, correlates with increased palmitic acid and fatty acid absorption, and thus lower concentrations of such are found in stool samples. A possible added benefit of milk fat based formula is lower levels of oleic and linoleic soaps found in the stool compared to vegetable oil formulas. It was also observed that the milk fat groups had lower levels of calcium excretion which indicated that the infants’ calcium absorption was aided and improved. Previous studies have shown that a higher concentration of sn-2 palmitic acid yields improved bone strength in infants. Compared to breast fed infants, formula fed infants typically have harder stools associated with the high content of fatty acid soaps in their stool. Although the study did not yield a definitive change in palmitic acid stool concentration between milk fat and vegetable oil formulas, milk fat based formulas have demonstrated positive effects on infant stool consistency. Overall, studies indicate the infant formulas that are enriched by bovine milk have a closer composition to human breast milk and are beneficial compared to vegetable oil based formulas (8). References

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