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.