Table 1.

Summary table of case-control studies regarding metabolite production and obesity.

Sample Size	Metabolites Involved	Biological Samples Analyzed	Results	References
208 obese subjects vs. 191 normal-weight subjects	Acetate, propionate, valerate, butyrate	Serum and stool	Higher concentrations of acetate (SMD = 0.87, 95% CI = 0.24–1.50), propionate (SMD = 0.86, 95% CI = 0.35–1.36), valerate (SMD = 0.32, 95% CI = 0.00–0.64) and butyrate (SMD = 0.78, 95% CI = 0.29–1.27) in obese subjects vs. normal-weight subjects	Kim KN et al., 2019 [53]
13 obese subjects vs. 13 normal-weight subjects	Acetate, butyrate	Stool	Acetate and butyrate were significantly higher in the group of obese patients compared to normal-weight patients (p = 0.033 and p = 0.004, respectively)	Martínez-Cuesta et al., 2021 [54]
92 obese adults vs. 92 normal-weight subjects	Leptin	Serum	Higher levels of leptin (51.24 ± 18.12 vs. 9.10 ± 2.99: p < 0.0001) in obese adults as compared to healthy control subjects	Kumar et al., 2020 [55]
35 obese adults vs. 20 normal-weight subjects	Leptin	Serum	Significant difference (p < 0.001) in leptin between the obese group (34.78 ± 13.96 ng/mL) and the non-obese control subjects (10.6 ± 4.2 ng/mL)	Al Maskari MY et al., 2006 [56]
1125 obese adults vs. 738 normal-weight subjects	Ghrelin	Serum	Lower levels of acyl ghrelin at baseline (SMD: −0.85; 95% CI: −1.13 to −0.57; p < 0.001) and postprandial at different time points (SMD 30 min: −0.85, 95% CI: −1.18 to −0.53, p < 0.001; SMD 60 min: −1.00, 95% CI: −1.37 to −0.63, p < 0.001; SMD 120 min: −1.21, 95% CI: −1.59 to −0.83, p < 0.001) in obese patients in respect to healthy control subjects	Wang Y. et al., 2022 [57]