The Association between the Firmicutes/Bacteroidetes Ratio and Body Mass among European Population with the Highest Proportion of Adults with Obesity: An Observational Follow-Up Study from Croatia

Abstract

Background/Objectives: The phyla Firmicutes and Bacteroidetes are the main constituents of the gut microbiota. An imbalance in the gut microbiota is a sign of dysbiosis, and the Firmicutes-to-Bacteroidetes ratio has been proposed to be a marker of it, especially in the context of obesity. Since Croatia is the country with one of the highest obesity rates in Europe, a pilot observational study was conducted. The aim of the study was to investigate the validity of this potential biomarker in a methodological study using sample processing, DNA sequence analysis and characterization of recruited participants, including various health factors. Methods: A study involving Croatian population was conducted. Participants age, body weight, gender, health history and lifestyle factors were recorded. Gut microbiota composition was analyzed using 16S rRNA sequencing. The F/B ratio was calculated and evaluated in the context of health factors. Statistical analysis was performed to detect the possible association of F/B ratio and excess body weight (kg) and possible impact of certain lifestyle factors. Results: No association between the F/B ratio and excess body weight (kg) was found. Excess body weight was significantly associated with higher age, male gender, and history of appendectomy. No significant health predictors of the F/B ratio were found, but weight gain was positively associated with a higher average F/B ratio. Conclusions: Although this study could not confirm the predictive value of the F/B ratio or any other phyla-related biomarker for excess body weight in the study population, it demonstrated interesting insights into the obesity-associated gut microbiota.

Keywords: Bacteroidetes; F/B ratio; Firmicutes; actinobacteria; adiposity; gut microbiome; gut microbiota; obesity.

Figure 1

Study concept.

Figure 2

Study flow.

Figure 3

Distribution of F/B ratio values in the study population for most participants (F/B ratio < 4.5).

Figure 4

Gut microbiome composition on the phyla level in the context of BMI: (a) BMI < 18.5 kg/m², (b) BMI = 18.5–24.9 kg/m², (c) BMI ≥ 25 kg/m². Abundance is defined by median and quartile values for each bacteria phylum.

Figure 5

Regression plots of BMI against relative proportions of phyla and (a) the Firmicutes/Bacteroidetes ratio (FB), (b) Actinobacteria, (c) Firmicutes, (d) Bacteroidetes, (e) Proteobacteria, and (f) Verrucomicrobia; r: Spearman’s correlation coefficient.