. 2023 Apr 4;2(2):e99. doi: 10.1002/imt2.99

Table 2.

Summary of obesity‐related gut microbial alterations reported in clinical studies.

Author (year)	Study design	Population characteristics	Intervention	Clinical findings (vs. lean/nonobese or baseline)
Evidence for: Low‐grade inflammation mediated by gut microbial dysbiosis
Andoh et al. (2016) [63]	Cross‐sectional study Fecal samples 16S rRNA sequencing	Japanese population: 10 obese, 10 lean Female: 50%, 50% Mean age (years): 41, 45 BMI (kg/m²): 38.1 ± 3.5, 16.6 ± 1.0	N/A	Microbial α‐diversity ↓ Phylum: Firmicutes ↑; Fusobacteria ↑ Genus: Alistipes, Anaerococcus, Coprococcus, Fusobacterium, and Parvimonas ↑; Bacteroides, Faecalibacterium, Desulfovibrio, Lachnoanaerobaculum, Olsenella ↓ Anti‐inflammatory bacteria species: Faecalibacterium prausnitzii ↓ Proinflammatory bacteria species: Bacteroides vulgatus ↑
Turnbaugh et al. (2009) [72]	Comparative study Fecal samples 16S rRNA sequencing Shotgun sequencing	European or African Female: 31 monozygotic twin pairs, 23 dizygotic twin pairs. Age range: 21–32 years Concordant for leanness (BMI: 18.5–24.9 kg/m²) or obesity (BMI ≥ 30 kg/m²)	N/A	Microbial α‐diversity ↓ Phylum Firmicutes (ns) Phylum Bacteroidetes ↓ Phylum Actinobacteria ↑ F/B ratio ↑
Haro et al. (2015) [77]	Clincal trial Fecal samples 16S rRNA sequencing	20 obese men: Age: 63.3 ± 2.0 years BMI: 32.2 ± 0.5 kg/m²	Two dietary interventions: ① Med (n = 10) ② LFHCC (n = 10) duration: 1 year	Med diet: Genus: Prevotella ↓; Roseburia, Oscillospira ↑ Species: Parabacteroides distasonis ↑ LFHCC diet: Genus: Prevotella ↑; Roseburia ↓ Species: Faecalibacterium prausnitzii ↑
Lee et al. (2019) [78]	Clincal trial Fecal samples 16S rRNA sequencing	12 obese women: Age: 52.5 (32–62) years BMI: 37.0 (31.0–40.5) kg/m²	BS: ① MWL (n = 4) ② AGB (n = 4) ③ RYGB (n = 4)	RYGB (at 10% weight‐loss): Microbial α‐diversity ↑ Phylum: Proteobacteria ↑; Actinobacteria ↑ Species: Faecalibacterium prausnitzii ↑
Aron‐Wisnewsky et al. (2019) [82]	Clinical trial Fecal samples Shotgun sequencing	61 severe obese women: Age: 36.9 ± 9.86 years BMI: 45.6 ± 5.23 kg/m²	BS: ① AGB (n = 20) ② RYGB (n = 41)	Baseline: Microbial gene richness ↓ 1‐year postsurgery: Microbial gene richness ↑
Evidence for: Increased phylum Firmicutes and/or decreased phylum Bacteroidetes (increased F/B ratio)
Koliada et al. (2017) [68]	Cross‐sectional study Fecal samples 16S rRNA sequencing	Ukrainian population: 11 obese, 16 overweight 27 normal, 7 underweight Female: 75% Mean age: 44.2 years	N/A	Phylum Firmicutes ↑ Phylum Bacteroidetes ↓ F/B ratio ↑
Rahat‐Rozenbloom et al. (2014) [69]	Observational study Faecal samples Rectal dialysis bag 16S rRNA sequencing	University of Toronto: 11 overweight, 11 lean Female: 45%, 45% Age (years): 42.5 ± 3.9, 35.8 ± 4.2 BMI (kg/m²): 30.1 ± 0.8, 22.6 ± 0.6	N/A	Phylum Firmicutes ↑ Phylum Bacteroidetes (ns) F/B ratio ↑
Ley et al. (2006) [70]	Clinical trial Fecal samples 16S rRNA sequencing	12 obese Age range: 21–65 years BMI range: 30–43 kg/m² 2 lean (as blank control) Mean BMI: 23 kg/m² Mean age: 34 years	Weight‐loss diets: ① FAT‐R (n = 6) ② CARB‐D (n = 6) duration: 1 year	Baseline (obese vs. lean): Phylum Firmicutes ↑ Phylum Bacteroidetes ↓ F/B ratio ↑ 1‐year diet‐treatment: Phylum Firmicutes ↓ Phylum Bacteroidetes ↑ F/B ratio ↓
Evidence against: Increased phylum Firmicutes and/or decreased phylum Bacteroidetes (increased F/B ratio)
Schwiertz et al. (2010) [73]	Cross‐sectional study Fecal samples 16S rRNA sequencing	University of Giessen and Marburg: 30 obese, 35 overweight, 33 lean Female: 65%. Age: 47 ± 13 years	N/A	Proportion of Firmicutes ↓ Proportion of Bacteroidetes ↑ F/B ratio ↓
Kellerer et al. (2019) [74]	Clincal trial Fecal samples 16S rRNA sequencing	German population: 17 morbidly obese, 17 nonobese Female: 82%, 82% Age (years): 41.8 ± 9.1, 41.7 ± 9.7 BMI (kg/m²): 52.5 (47.0–56.8), 21.5 (19.6–23.3). BMI‐LSG: 39.1 (32.6–44.0) kg/m² Nonobese as blank control	BS: LSG Follow‐up: 6‐month	Baseline (obese vs. nonobese): Phylum Firmicutes ↓ Phylum Bacteroidetes ↑ F/B ratio ↓ LSG (6‐month follow‐up): Phylum Firmicutes ↑ Phylum Bacteroidetes ↓ F/B ratio ↑
Duncan et al. (2008) [75]	Clincal trial Fecal samples 16S rRNA sequencing	North of Scotland: 29 obese men (BMI > 30 kg/m²) 14 nonobese (BMI < 30 kg/m²) Balanced cross‐over design: (on 23 obese individuals)	Weight‐loss diets: ① LC for 4 weeks ② MC for 4 weeks duration: 8 weeks	Cross‐sectional and clincal trial: Phylum Firmicutes (ns) Phylum Bacteroidetes (ns)

Author (year)

Study design

Population characteristics

Intervention

Clinical findings (vs. lean/nonobese or baseline)

Evidence for: Low‐grade inflammation mediated by gut microbial dysbiosis

Andoh et al. (2016) [63]

Cross‐sectional study

Fecal samples

16S rRNA sequencing

Japanese population:

10 obese, 10 lean

Female: 50%, 50%

Mean age (years): 41, 45

BMI (kg/m²): 38.1 ± 3.5, 16.6 ± 1.0

N/A

Microbial α‐diversity ↓

Phylum: Firmicutes ↑; Fusobacteria ↑

Genus: Alistipes, Anaerococcus,

Coprococcus, Fusobacterium, and

Parvimonas ↑; Bacteroides,

Faecalibacterium, Desulfovibrio,

Lachnoanaerobaculum, Olsenella ↓

Anti‐inflammatory bacteria species:

Faecalibacterium prausnitzii ↓

Proinflammatory bacteria species:

Bacteroides vulgatus ↑

Turnbaugh et al. (2009) [72]

Comparative study

Fecal samples

16S rRNA sequencing

Shotgun sequencing

European or African Female:

31 monozygotic twin pairs,

23 dizygotic twin pairs.

Age range: 21–32 years

Concordant for leanness (BMI:

18.5–24.9 kg/m²) or obesity (BMI ≥ 30 kg/m²)

N/A

Microbial α‐diversity ↓

Phylum Firmicutes (ns)

Phylum Bacteroidetes ↓

Phylum Actinobacteria ↑

F/B ratio ↑

Haro et al. (2015) [77]

Clincal trial

Fecal samples

16S rRNA sequencing

20 obese men:

Age: 63.3 ± 2.0 years

BMI: 32.2 ± 0.5 kg/m²

Two dietary interventions:

① Med (n = 10)

② LFHCC (n = 10)

duration: 1 year

Med diet:

Genus: Prevotella ↓; Roseburia, Oscillospira ↑

Species: Parabacteroides distasonis ↑

LFHCC diet:

Genus: Prevotella ↑; Roseburia ↓

Species: Faecalibacterium prausnitzii ↑

Lee et al. (2019) [78]

Clincal trial

Fecal samples

16S rRNA sequencing

12 obese women:

Age: 52.5 (32–62) years

BMI: 37.0 (31.0–40.5) kg/m²

BS:

① MWL (n = 4)

② AGB (n = 4)

③ RYGB (n = 4)

RYGB (at 10% weight‐loss):

Microbial α‐diversity ↑

Phylum: Proteobacteria ↑; Actinobacteria ↑

Species: Faecalibacterium prausnitzii ↑

Aron‐Wisnewsky et al. (2019) [82]

Clinical trial

Fecal samples

Shotgun sequencing

61 severe obese women:

Age: 36.9 ± 9.86 years

BMI: 45.6 ± 5.23 kg/m²

BS:

① AGB (n = 20)

② RYGB (n = 41)

Baseline:

Microbial gene richness ↓

1‐year postsurgery:

Microbial gene richness ↑

Evidence for: Increased phylum Firmicutes and/or decreased phylum Bacteroidetes (increased F/B ratio)

Koliada et al. (2017) [68]

Cross‐sectional study

Fecal samples

16S rRNA sequencing

Ukrainian population:

11 obese, 16 overweight

27 normal, 7 underweight

Female: 75%

Mean age: 44.2 years

N/A

Phylum Firmicutes ↑

Phylum Bacteroidetes ↓

F/B ratio ↑

Rahat‐Rozenbloom

et al. (2014) [69]

Observational study

Faecal samples

Rectal dialysis bag

16S rRNA sequencing

University of Toronto:

11 overweight, 11 lean

Female: 45%, 45%

Age (years): 42.5 ± 3.9, 35.8 ± 4.2

BMI (kg/m²): 30.1 ± 0.8, 22.6 ± 0.6

N/A

Phylum Firmicutes ↑

Phylum Bacteroidetes (ns)

F/B ratio ↑

Ley et al. (2006) [70]

Clinical trial

Fecal samples

16S rRNA sequencing

12 obese

Age range: 21–65 years

BMI range: 30–43 kg/m²

2 lean (as blank control)

Mean BMI: 23 kg/m²

Mean age: 34 years

Weight‐loss diets:

① FAT‐R (n = 6)

② CARB‐D (n = 6)

duration: 1 year

Baseline (obese vs. lean):

Phylum Firmicutes ↑

Phylum Bacteroidetes ↓

F/B ratio ↑

1‐year diet‐treatment:

Phylum Firmicutes ↓

Phylum Bacteroidetes ↑

F/B ratio ↓

Evidence against: Increased phylum Firmicutes and/or decreased phylum Bacteroidetes (increased F/B ratio)

Schwiertz et al. (2010) [73]

Cross‐sectional study

Fecal samples

16S rRNA sequencing

University of Giessen and Marburg:

30 obese, 35 overweight, 33 lean

Female: 65%.

Age: 47 ± 13 years

N/A

Proportion of Firmicutes ↓

Proportion of Bacteroidetes ↑

F/B ratio ↓

Kellerer et al. (2019) [74]

Clincal trial

Fecal samples

16S rRNA sequencing

German population:

17 morbidly obese, 17 nonobese

Female: 82%, 82%

Age (years): 41.8 ± 9.1, 41.7 ± 9.7

BMI (kg/m²): 52.5 (47.0–56.8),

21.5 (19.6–23.3).

BMI‐LSG: 39.1 (32.6–44.0) kg/m²

Nonobese as blank control

BS: LSG

Follow‐up:

6‐month

Baseline (obese vs. nonobese):

Phylum Firmicutes ↓

Phylum Bacteroidetes ↑

F/B ratio ↓

LSG (6‐month follow‐up):

Phylum Firmicutes ↑

Phylum Bacteroidetes ↓

F/B ratio ↑

Duncan et al. (2008) [75]

Clincal trial

Fecal samples

16S rRNA sequencing

North of Scotland:

29 obese men (BMI > 30 kg/m²)

14 nonobese (BMI < 30 kg/m²)

Balanced cross‐over design:

(on 23 obese individuals)

Weight‐loss diets:

① LC for 4 weeks

② MC for 4 weeks

duration: 8 weeks

Cross‐sectional and clincal trial:

Phylum Firmicutes (ns)

Phylum Bacteroidetes (ns)

Abbreviations: AGB, adjustable gastric banding; BMI, body mass index; BS, Bariatric surgery; CARB‐R, carbohydrate‐restricted; FAT‐R, fat‐restricted; LC, high‐protein low carbohydrate, ketogenic; LFHCC, a low‐fat, high‐complex carbohydrates diet; LSG, laparoscopic sleeve gastrectomy; MC, high‐protein moderate‐carbohydrate, non‐ketogenic; Med, Mediterranean diet; MWL, medical weight loss; rRNA, ribosomal RNA; RYGB, Roux‐en‐Y‐gastric bypass.