Prebiotics are defined as non-digestible food ingredients that have the ability to enhance the growth and/or activity of bacteria that may be beneficial to health. Natural prebiotic oligosaccharides have been detected in human breastmilk (human milk oligosaccharides (HMOs)) with much work conducted to establish the beneficial role of these HMOs in infant microbiota. HMOs are the third largest component of human milk and have been shown to modulate the infant immune system as well as influence the development of the gut microbiota. Dietary oligosaccharide structures that have prebiotic effects similar to HMOs include galacto-oligosaccharides (GOS), fructo-oligosaccharides (FOS), and pectin-derived acidic oligosaccharides. GOS and FOS are non-digested components of legumes, wheat and rye products, onion and garlic. HMOs, GOS and FOS escape digestion. This process enables them to move through to the colon and exert their prebiotic effects.
As the composition of breastmilk is further defined infant formula is constantly being reformulated to mimic breastmilk. Research into prebiotic oligosaccharides and HMOs has led to the supplementation of infant formula with prebiotic GOS, FOS or both.
Studies have been conducted to investigate the effect of GOS alone, or with FOS (ratio 9:1) at varying concentrations demonstrating that the levels of Bifidobacterium spp. in faecal bacterial populations are higher than in infants receiving unsupplemented formula(1-7). In fact the addition of a prebiotic GOS/FOS mixture to an infant formula exerts changes in short chain fatty acids, lactate and pH that resemble the fermentation profile observed in breast fed infants(1). Concurrently, stimulation of bifidobacteria reduces the presence of clinically relevant pathogens in the faecal flora, indicating that prebiotic substances might have the capacity to protect against intestinal infections(8). In adult subjects, prebiotic supplementation has also been shown to benefit gut health with reductions in IBS symptoms(3) and the incidence of traveller’s diarrhoea(9).
There are other documented benefits of prebiotic GOS and/or FOS in infant formula. A dose-dependent effect on stool consistency has been demonstrated, with increasing dosage leading to softer stool similar to breastfed infants(2,5). In addition, GOS as a choice of prebiotic produces the least amount of gas compared to other common prebiotic ingredients, which greatly assists tolerance(7). Immune effects have been demonstrated with GOS supplementation increasing phagocytosis, natural killer cell activity, and the production of anti-inflammatory interleukin-10 (IL-10), and of proinflammatory cytokines (IL-6, IL1? and tumour necrosis factor-?)(10). The mechanism is unknown but effects are likely secondary to the bifidobacteria increase induced by prebiotic supplementation. Indeed probiotic supplementation of bifidobacteria has similar benefits to prebiotics on the immune system(11-13). It is important to note that the effects of GOS in infant formula may only be seen when administration is begun in early infancy(14). In addition, bacterial populations return to baseline levels within one to two weeks after GOS consumption was stopped(4).
A Cochrane review on the role of prebiotics in the prevention of allergy(15) concluded that there is some evidence that a prebiotic supplement added to infant feeds may prevent eczema, but not asthma or urticaria. This research stems from the fact that there are lower concentrations of bifidobacteria and higher concentrations of clostridia and Staphylococcus aureus within the first year of life in infants who develop allergies. Such findings highlight the role of microbiota in allergies giving rise to the potential for benefits by manipulating the bacterial profile of the gut(16). It is however, unclear whether any benefit with the use of prebiotic is likely to be seen only in infants at high risk of allergy. Further research is needed before routine use of prebiotics can be recommended for prevention of allergy.
From this and other research, it is clear that breastfeeding provides the best source of nutrition for infants including exposure to HMOs. When breastfeeding is not possible, the evidence suggests that infant formula supplemented with prebiotics gives the infant a similar colonic microbial environment to that in breastfed infants. In practice, breastfeeding or use of a prebiotic supplemented formula will provide prebiotics in early infancy, with naturally occurring prebiotics consumed as intake of solids commence.