Fiber effects on the microbiome
Certain fibers, also termed microbiota-accessible carbohydrates, are an
essential food source for the microbiome in that they provide resources
for microbial growth. They are central to food-webs in the gut
microbiota established through cross-feeding, and reduced fiber intake
has been shown to be associated with the loss of ancestral
microbes.12 Overall, species diversity and richness
have been shown to be reduced by about one third in North Americans
compared to Malawians or Amerindians, which might be due in part to
changes in dietary fiber consumption.13 A high fat/low
fiber diet and obesity have been associated with alterations in gut
microbiota composition and metabolic activity.14,15The degradation of dietary fibers requires specific CAZymes
(carbohydrate active enzymes), which are not encoded in the human
genome, but are encoded in the genomes of specific bacterial
strains.16,17 Therefore specific subsets of microbes
are supported by different types of dietary fibers, which highlights the
potential for using selected fiber structures to achieve targeted
functional, metabolic, and perhaps immunological
outcomes.18 During the neonatal period, human milk
oligosaccharides (HMOs) selectively support the growth of someBifidobacterium and Bacteroideteslineages.19,20 Following on from breast feeding,
complementary feeding and weaning drives a diversification of the gut
microbiota towards an adult-like state. However, the relative
contribution for each of these newly introduced dietary fibers
post-weaning on microbiome development, and how this relates to
development of the immune system, has not been adequately studied.