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Table 1 Key studies describing the gut microbiota and its relationship to different geographical locations (A), and key studies describing the gut microbiota and its relationship to obesity (B) are indicated

From: The obese gut microbiome across the epidemiologic transition

Author Groups Geographical effect
A
 De Filippo et al. [77] Rural Africa vs. Italian children (1–6 years) Species differences existed that conferred specific nutritional effects
 Lee et al. [50] Monozygotic and dizygotic US vs. Korean twins, either normal weight (BMI < 25 kg/m2) or overweight (BMI > 25 kg/m2) Significant differences in configuration fecal communities between sites
 Yatsunenko et al. [49] Venezuelan (Amerindians), Malawian, US children (0–17 years) and adults (18–70 years) Phylogenetic and microbiota enzymatic differences
 Tyakht et al. [81] Urban vs. rural Russian males and females (14–85 years) Phylogenetic differences existed
 Karrlson et al. [28] Type 2 diabetes, normal- and impaired-glucose tolerance older European women (>70 years) vs. type 2 diabetes, normal and impaired glucose tolerance Chinese men and women (13–86 years) Metagenomic cluster differed between two populations
 David et al. [51] Two US adult males (26, and 36 years) Travel acutely altered phylogenetic taxa
Author Groups Obesity effect
B
 Backhed et al. [52] Conventionally raised vs. germ-free and germ-free conventionalized Conventional had significantly more body fat than germ-free, as did conventionalized, both eating less chow
 Ley et al. [30] Lean vs. obese humans Relative proportion of Bacteroidetes is reduced in obesity
 Turnbaugh et al. [21] Ob/ob mice vs. ob/+ and +/+mice Ob/ob mice increased rate of energy harvest from diet, transmission of ob/ob gut microbiome to +/+ resulted in significantly greater increase in body fat
 Turnbaugh et al. [24] Lean (BMI < 25 kg/m2) and overweight (BMI ≥ 25 kg/m2) or obese (BMI ≥ 30 kg/m2) twins Lower proportion Bacteroidetes and higher proportion of Actinobacteria in obese vs. lean twins. No difference in Firmicutes between twins
 Turbbaugh et al. [25] Germ-free mice colonized with human gut microbiota, fed either low-fat, plant polysaccharide-rich or high fat (Western) diet Increase in proportion of Firmicutes and decrease in proportion of Bacteroidetes in mice fed western diet. Off-spring from either germ-free or humanized mice indicated gut microbiome could be transmitted, sharing 83 % of class-level Taxa and 73 % genus level
 Murphy et al. [56] Ob/ob mice vs. wild type on high- or low-fat diet Increase in Firmicutes in high-fat and ob/ob. Reduction in Bacteroidetes in ob/ob only
 Lee et al. [50] US vs Korean Lower alpha-diversity in obesity, regardless of site
 Ridaura et al. [22] Germ-free mice transplanted with fecal microbiota from twins discordant for obesity (obese twin BMI ≥ 30 kg/m2) Mice receiving obese fecal microbiota had significantly greater increase in adipose mass. Feces from mice with obese fecal microbiota had higher branched chain amino acids