Nearly 3.1 million children under five die every year due to poor nutrition, according to the World Food Programme, the world’s largest humanitarian agency fighting hunger. One in six infants (roughly 100 million) is underweight and the growth of 25% of children worldwide is stunted, a disabling consequence of malnutrition and frequent or persistent infections that undermine children’s health and put them at risk of cognitive impairment, immune diseases and death.
Now, according to a new study recently published in Cell, gut microbiota could also play a key role in children’s growth. Scientists from the Washington University School of Medicine in St Louis, led by Jeffrey L Gordon, have observed that some oligosaccharides found in breast milk can stimulate the activity of certain growth-promoting microbes following research with two animal models of infant malnutrition.
The researchers partnered with colleagues in Malawi, an African country where almost 50% of children under five show stunted growth. They analysed samples of human breast milk from the mothers of two groups of six-month-old babies – one consisting of healthy babies and the other with infants who were showing stunted growth. With this approach, the researchers were interested in seeing what happened to oligosaccharides, a type of sugar that humans cannot digest and which are broken down by the bacteria in our gut.
They observed that two types of oligosaccharides – sialylated (involved in brain development, for instance) and fucosylated – were much more abundant in the breast milk of women with healthy children in comparison to the breast milk of those whose babies showed signs of stunted growth. The authors therefore highlight in their paper that these results may suggest these breast milk sugars could promote healthy growth in infants.
To test if this was the case, they transferred a bacterial cocktail from faecal samples of the malnourished children into germ-free mice. It was subsequently observed that only 19 out of the 25 bacterial strains introduced into the animals successfully colonised the murine gut. For five further weeks, two groups of rodents (one germ-free and the other that had received the transplanted bacteria) were fed two different diets. The former was a mash of the same food typically eaten by Malawian children (based on corn, legumes, vegetables and fruit), which is inadequate for healthy growth. The latter was the same diet enriched with sialylated oligosaccharides from cow’s milk (which contains a concentration of these sugars 20 times lower than breast milk) or a combination of fructose polymers commonly found in infant formulas.
At the end of the 5-week period, the researchers observed that the transplanted mice fed the Malawian diet together with milk sugars had gained more weight and put on more muscle, while developing denser bones and experiencing metabolic changes in the liver and the brain, all in comparison to the germ-free animals. That suggests that the gut microbiota may play a critical role in the effect of the oligosaccharides on healthy infant growth.
The results also indicate that breastfeeding may promote a positive gut environment for essential microbes to proliferate and encourage healthy growth in babies. The article’s authors speculate that a possible explanation for this may be that bacteria process those sugars and in turn produce molecular building blocks to help the host’s body grow properly. Apart from mice, the researchers tested their results on piglets (which are physiologically more similar to humans than mice) and noted the same outcome.
Although further research is needed, this work lays the foundation for identifying the components of breast milk needed for infant health and how they interact with the gut microbiota and other dietary components. It could also open the door to improving infant formulas and therapeutic food used to treat malnutrition, both of which are currently based on cow’s milk and are therefore deficient in sialylated sugars.
Charbonneau et al.: “Sialylated Milk Oligosaccharides Promote Microbiota-Dependent Growth in Models of Infant Undernutrition” Cell, http://dx.doi.org/10.1016/j.cell.2016.01.024