Dr Bernd Stahl, R&D Director of Human Milk Research at Nutricia Research, Utrecht, Netherlands, discusses the results of research into the anti-allergenic effect of beneficial bacteria within the gut, and how their activity and numbers might be encouraged with specific non-digestible oligosaccharides.
WHO recommends exclusive breastfeeding for the first six months after which breastfeeding can continue alongside suitable, complementary, solid foods1. One of the many reasons for recommending exclusive breastfeeding for the first six months of life is that breastfed infants have lower levels of atopic disease compared to those fed on infant formula2.
Breastmilk achieves this beneficial effect through a number of factors, many of which are not completely understood.
“One mechanism that has been researched increasingly in recent years is the way that compounds within breastmilk stimulate the growth of ‘friendly’ bacteria in the gut of the growing infant.”
The intestinal tract of the unborn infant is relatively sterile. During vaginal delivery and as the infant starts to breastfeed, the infant comes into contact with ‘friendly’ bacteria such as Bifidobacteria and Lactobacilli which enter the gut and gradually begin to colonise it3.
Human milk oligosaccharides
The bacterial population creates an intestinal ‘microbiota’ whose composition plays an important role in the infant’s digestion, protects against the development of pathogenic bacteria such as E coli, Clostridia and Eubacteria and stimulates the development of the immune system4.
Studies have shown significant differences between the microbiota of breastfed and bottlefed infants5 and also between infants with and without atopic disease6. A microbiota with high levels of Bifidobacteria and low counts of Clostridia is associated with a reduced risk of allergy7.
“A crucial constituent of breastmilk that contributes to the growth of beneficial bacteria is a class of compounds known as human milk oligosaccharides (HMOS).”
HMOS cannot be digested by the infant. But unlike dietary fibre, which passes through the infant’s gut virtually unchanged, HMOS are selectively fermented by the beneficial bacteria. Products of this fermentation include short-chain fatty acids which are absorbed by the infant and lower the pH of the gut to levels that inhibit the growth of pathogens3.
The link between the gut microbiota and subsequent development of atopic disease has led a number of researchers to investigate whether non-digestible or fermentable compounds could be used as a nutritional ingredient to modify the infant gut microflora and thus help protect against atopic dermatitis (or atopic eczema) and allergic symptoms (or manifestations).
In several dietary intervention studies researchers used a mixture of short chain galacto-oligosaccharides and long-chain fructo-oligosaccharides (GOS/FOS 9:1) to mimic the effect of oligosaccharides within breastmilk8. The study enrolled healthy, full-term babies born to parents with a history of atopic eczema, allergic rhinitis or asthma.
The infants’ mothers were all advised to breastfeed their infants, but those who switched to formula feeding within the first two weeks were randomly assigned to a formula milk that was supplemented either with the GOS/FOS 9:1 carbohydrates or an inactive carbohydrate placebo. Of these infants, 134 were followed up for two years8.
The results showed that, by the end of the study, the infants fed GOS/FOS 9:1 formula had a significantly lower incidence of atopic dermatitis, recurrent wheezing and allergic urticaria compared to the placebo group8.
A more recent follow-up to that study of 92 children has shown the anti-allergenic effect of the GOS/FOS 9:1 mixture and showed that, in high-risk infants, the reduced risk of atopic dermatitis and certain allergic symptoms lasts beyond infancy until at least five years of age9.
Halting the allergic march
The importance of offering protection against atopic dermatitis and certain allergic symptoms is two-fold. Not only is the condition unpleasant and irritating for the child at the time, it is also considered one of the stages in the paediatric ‘allergic march’ in which allergies might follow atopic dermatitis to allergic rhinoconjunctivitis and finally to asthma. Childhood allergy places a significant burden on the NHS, and any intervention that can halt or avoid the onset of this progression and reduce the need for treatment is to be welcomed.
Naturally occurring oligosaccharides in breastmilk are just one of the many remarkable ways in which breastfeeding offers infants the very best start in life. The more we learn about the various constituents within breastmilk (including recently discovered small amounts of <>bifidobacteria and lactobacilli), the more we understand how the benefits of breastfeeding extend beyond nutrition and into the realms of immune system development.