Table 1. Gut Microbiota Composition Throughout the Life Span.

	Composition	References
Neonatal	Low diversity and a relative dominance of the phyla Proteobacteria and Actinobacteria	Eckburg et al (2005), Qin et al (2010)
Adult	Dominated by members of the Bacteroidetes and Firmicutes phyla	Turnbaugh et al (2006)
Old age	Bacteroides and Firmicutes are the dominant phyla Significant loss of diversity especially in frail elderly	Claesson et al (2011)