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Fortified milk containing synbiotics, micronutrients, and with reduced protein content holds promise for elevating iron status and improving overall gut health in toddlers, according to an industry-funded study.
January 27, 2025
Published in Frontiers in Pediatrics, the study – part of a series of Child Health and Residence Microbes (CHaRM) studies from the University of Queensland, Australia, on gut health in toddlers – investigated the impact of fortified milk versus unfortified cow's milk on the gut microbiota of children aged one to two years.
The double-blind, randomised control trial took place over a 12-month period in a small cohort of children, funded by an investigator-initiated grant from Danone Nutricia Australia.
The active group of toddlers received fortified milk with reduced protein content supplemented with a synbiotic blend of Bifidobacterium breve M-16V, short-chain galactooligosaccharides [scGOS], and long-chain fructooligosaccharides [lcFOS]. The milk was also fortified with iron, vitamin D, and vitamin C.
Healthy children who consumed the synbiotic-fortified formula as part of a healthy diet demonstrated improved iron availability and absorption in the gut, as well as an increased abundance of Bifidobacterium in their gut microbiome, findings suggested.
“At the end of the intervention, we observed significant differences in several blood parameters; serum iron, transferrin, and haemoglobin levels were higher in the active group at month 12 compared to baseline,” the researchers wrote.
While the control group also showed “smaller, significant changes for the same corresponding parameters”, the researchers said toddlers who consumed the fortified milk finished with higher levels of serum iron in their blood and more Bifidobacterium in their gut microbiome.
“We hypothesise that the mode of action by which Bifidobacterium may improve host iron bioavailability is by (1) lowering the colonic luminal pH and (2) converting Fe3+ to Fe2+, due to their ferric-reducing activity,” they wrote.
“In addition, Bifidobacteria may prevent opportunistic pathogenic bacteria from utilising the scarce amount of iron either by (1) competitive exclusion or by (2) reducing Fe2+ accessibility for other microorganisms by competitively binding it to their extracellular membranes.”
The researchers said the improvement in iron status was important, given that young children's intake of micronutrients like iron is “usually sub-optimal” when based on regular dietary consumption, despite this population having higher needs than adults.
Iron, for example, plays an “important role in the normal development of mental and motor skills in children”.
And while iron-fortified foods and oral iron supplements present a means to address this, they are often associated with adverse effects such as diarrhoea and an increase in opportunistic pathogenic bacteria, or simply poor absorption, they said.
The study into fortified milk, therefore – specifically, iron-fortified milk blended with synbiotics – highlights a potential alternative for toddlers.
“Several studies have shown modulation of the colonic microbiota by pre-, pro-, or synbiotics can mitigate these adverse effects of iron fortification on the gut microbiome. This study confirms changes in both the taxonomic composition and the relative abundances of predicted microbial functions over one year, indicative of a developing early-life microbiome,” the researchers wrote.
The researchers said the study came with limitations, notably that findings were only reflective of a small cohort of clinically healthy children and so caution had to be taken in the interpretation of the results.
However, they said the study provided a “working hypothesis” on the effects that synbiotics have on gut microbiota composition and microbial function during toddlerhood, and shows that “in the presence of synbiotics, iron absorption may be improved through the acidification of the gut”.
Importantly, the study presents findings on toddlerhood – an area where studies remain sparce despite these years being an “important phase of life in which adequate nutrition with micro- and macronutrients is essential for growth and development”.
Danone Research and Innovation said the study underscored the “critical role of diet in early gut microbiota development” and indicated that fortified milk could have a “positive impact on both nutritional status and gut microbiome composition in young children”.