Given the known role of 2′-FL as a prebiotic capable of influencing the composition and metabolic function of the gut microbiome, and confer important benefits to immunity and gut health, researchers from the multinational medical devices and health care company hypothesised that supplementation of 2′-FL may have substantial effects on the metabolic output of the intestinal microbiome.
Researchers conducted a prospective, randomised, and double-blinded study in a previously studied cohort to examine circulating metabolite composition in infants fed one of several formula matrices differing only in their oligosaccharide content, relative to age-matched infants who were exclusively breastfed.
The report is a new component of a previous clinical study. Blood samples were collected from a subset of healthy, full-term infants who participated in a prospective growth study, conducted at 28 sites throughout the United States from April 2013 through January 201.
They found differences in circulating metabolite composition between breastfed infants and those who were fed a control infant formula. However fortification of infant formula with 2′-FL was associated with an increase in the abundance of microbial fermentation products.
They also observed that 2′-FL fortification resulted in a dose-dependent increase in the circulation of microbe-derived secondary bile acids. Secondary bile acids in circulation were associated with changes in circulating cytokine concentrations, suggesting changes to the systemic immune environment.
The authors explain these findings represent the first report linking human milk oligosaccharide consumption to the production of secondary bile acids by the gut microbiota in infants. These secondary bile acids play a putative role in the development and maintenance of immune homeostasis.
They conclude: "Taken together, these results suggest that 2′-FL fortification of infant formula may support aspects of microbial metabolism typically associated with breastfeeding."
Whilst breastfeeding is the gold standard in infant nutrition access to healthcare, cultural expectations, and employment outside the home can present significant challenges to exclusive and prolonged breastfeeding.
Significant progress has been made in recent years regarding the fortification of some infant formulas with Human Milk Oligosaccharides (HMOs). HMOs are the 3rd largest solid component of human milk with a broad range of potential benefits, including prebiotic effects and enhanced gut maturation, gut motility, immunity, and cognition. More than 150 unique HMO structures have been identified. Although the individual composition is highly variable, 2′-FL is among the most abundant naturally occurring HMOs with levels ranging from 0.06–4.65 g/L in human milk.
Clinical studies have demonstrated that supplementation of infant formula with 2′-FL is well tolerated and promotes systemic reduction in inflammatory cytokine levels relative to control formula and comparable to breastfed infants. Additional data from the same patient cohort indicated that infants fed formula fortified with 2′-FL experienced fewer respiratory infections relative to infants fed control formula. A similar study suggests that fortification of infant formula with 2′-FL and LNnT may be associated with lower rates of antibiotic use in young children.
Metabolomics is a growing field of research utilising high throughput liquid and gas chromatography, mass spectrometry, and nuclear magnetic resonance techniques to independently quantify and analyse vast numbers of unique metabolites in biological samples. Previous studies have compiled broad surveys of the metabolites present in breastmilk as well as the differences in circulating metabolites between breastfed and formula-fed infants. Studies examining the differences between formula-fed and breastfed infants have utilized a variety of techniques to measure 356 metabolite composition in stool, urine, and plasma samples collected from infants aged 0–24 months. However, wide variations in methodology, sample collection, and study populations have limited the generalizability and reproducibility of these studies.
The present study represents one of the largest surveys of the infant metabolome with 200 enrolled participants with a wider survey of metabolites (743 known metabolites) than previous reports (<200).
The original clinical trial enrolled 424 healthy infants who had exclusively either been fed formula or breastfed since birth, were enrolled by five days of life and exclusively formula-fed (n = 317) or breastfed (n = 107) from enrolment to 4 months of age.
As part of the original clinical trial, infants were randomly assigned to be fed 1 of 3 formulas, all containing a total amount of 2.4 g oligosaccharides/L, according to computer-generated randomisation. A nonrandomised BF group was also enrolled.
The control formula contained galacto-oligosaccharides (GOS) only; the experimental formulas (EFs) were fortified with varying amounts of 2′-FL and GOS (CF: 0 g 2′-FL/L + 2.4 g GOS/L; EF1: 0.2 g 2′-FL/L + 2.2 g GOS/L; EF2: 1 g 2′-FL/L + 1.4 g GOS/L).
Biological sampling involved urine, stool, and blood from infants and breast-milk samples from breastfeeding mothers.
Regarding potential limitations of this study, the authors note the absence of data on the composition of the faecal microbiota and faecal secondary bile acids. They also note that differences in intestinal absorption of secondary bile acids under different feeding conditions cannot be ruled out as a contributing factor in the observed differences in plasma secondary bile acids.
Extended metabolic activity
In the present study, the differences in metabolite profiles between infants fed control formula and those fed 2′-FL fortified formula extended beyond 2′-FL and its immediate catabolic products fucose and lactose, suggesting 2′-FL might support additional metabolic activity.
The team examined the levels of multiple bacterial fermentation products in formula-fed and breastfed infants and found 2′-FL fortification was associated with elevated levels of dicarboxylic acids, and medium and short-chain fatty acids typically associated with bacterial fermentation.
The report states: "In some cases, 2′-FL fortification resulted in the production of these metabolites at levels comparable to our observations in breastfed infants. This suggested that dietary 2′-FL acts as either a direct substrate for bacterial fermentation or that it supports the growth of strains that are participating in the fermentation of other dietary compounds."
Several secondary bile acids, notably 12-dehydrocholate, hyocholate, taurolithocholate 3-sulfate, taurocholenate sulfate, and glycolithocholate sulfate, were significantly higher in the circulation of breastfed infants relative to control formula-fed infants. A smaller subset of deoxycholate structures were elevated in control formula-fed infants relative to breastfed infants.
The researchers observed that fortification of infant formula with 2′-FL resulted in the increased abundance in plasma of many of the secondary bile acids associated with breastfeeding. In many cases, this relationship was dose-dependent with higher levels of 2′-FL fortification being correlated with higher levels of circulating secondary bile acids.
"Infants Fed Breastmilk or 2′-FL Supplemented Formula Have Similar Systemic Levels of Microbiota-Derived Secondary Bile Acids"
Authors: Hill, D. R., and Buck, R. H.