Associations of Fecal Microbiota with Ectopic Fat in African Caribbean Men

Abstract

Objective: The gut microbiome has been associated with visceral fat (VAT) in European and Asian populations; however, associations with VAT and with ectopic fats among African-ancestry individuals are not known. Our objective was to investigate cross-sectional associations of fecal microbiota diversity and composition with VAT and ectopic fat, as well as body mass index (BMI), among middle-aged and older African Caribbean men.

Methods: We included in our analysis n = 193 men (mean age = 62.2 ± 7.6 years; mean BMI = 28.3 ± 4.9 kg/m²) from the Tobago Health Study. We assessed fecal microbiota using V4 16s rRNA gene sequencing. We evaluated multivariable-adjusted associations of microbiota features (alpha diversity, beta diversity, microbiota differential abundance) with BMI and with computed tomography-measured VAT and ectopic fats (pericardial and intermuscular fat; muscle and liver attenuation).

Results: Lower alpha diversity was associated with higher VAT and BMI, and somewhat with higher pericardial and liver fat. VAT, BMI, and pericardial fat each explained similar levels of variance in beta diversity. Gram-negative Prevotellaceae and Negativicutes microbiota showed positive associations, while gram-positive Ruminococcaceae microbiota showed inverse associations, with ectopic fats.

Conclusions: Fecal microbiota features associated with measures of general adiposity also extend to metabolically pernicious VAT and ectopic fat accumulation in older African-ancestry men.

Keywords: adiposity; body fat distribution; microbiome; obesity.

Figure 1

Relative abundance plots of fecal microbiota by quartile of VAT among men from the Tobago Health Study. A total of 193 men were included in the analyses. Participants were grouped into quartiles of VAT. The top 5 most abundant phyla and the top 10 most abundant genera in the overall study sample are shown; the remaining taxa are grouped together into an “Other” category. Abbreviations: VAT = visceral fat.

Figure 2

PCoA plots of Bray-Curtis dissimilarity by quartiles of BMI and VAT among men from the Tobago Health Study. A total of n = 193 men were included in the analyses. Participants were grouped into quartiles of BMI or VAT. Fecal microbiota samples were first rarefied to a sequencing depth of 1500 reads, and then the Bray-Curtis dissimilarity was calculated for each pair of samples. PCoA plots were constructed to visualize the separation of samples, such that the samples located closer together had more similar microbial compositions. A 95% ellipse was calculated for each BMI or VAT quartile. Panels: (A) BMI quartiles; (B) VAT quartiles. Abbreviations: PCoA = principal coordinates analysis; VAT = visceral fat.

Figure 3

Heatmap and relative abundance plots for associations of microbial OTUs with standard deviation increment in BMI or fat measures. A total of n = 193 men were included in the analyses. Rare (prevalence of <10%) and low-abundant (mean relative abundance < 0.1%) microbes were pre-filtered from samples. ANCOM-BC models were analyzed separately for each BMI or fat measure; models adjusted for age (years), educational attainment (primary, secondary, or post-secondary), hours walked per week for exercise (hours), current smoking status (yes vs. no), drinking 4 or more alcoholic drinks per week (yes vs. no), and the time difference between CT scans and fecal sample collection (years). Heatmap (left): The log-fold difference in microbial abundance per standard deviation increment in BMI or fat measure. Asterisks (*) indicate significant associations at FDR-corrected q < 0.05. Note: lower muscle attenuation or lower liver attenuation reflects greater lipid accumulation. Relative abundance plot (right): Strip plot showing the relative abundance of each OTU. Colors of strip plots reflect the percent non-zero prevalence of the OTU across the analytic sample. Abbreviations: OTU = operational taxonomic unit; ANCOM-BC = Analysis of Compositions of Microbiomes with Bias Correction; FDR = false discovery rate; IMAT = intermuscular fat; SD = standard deviation.