Herbs and Spices Modulate Gut Bacterial Composition in Adults at Risk for CVD: Results of a Prespecified Exploratory Analysis from a Randomized, Crossover, Controlled-Feeding Study

Abstract

Background: Herbs and spices are rich in polyphenolic compounds that may influence gut bacterial composition. The effect of culinary doses of herbs and spices consumed as part of a well-defined dietary pattern on gut bacterial composition has not been previously studied.

Objectives: The aim of this prespecified exploratory analysis was to examine gut bacterial composition following an average American diet (carbohydrate: 50% kcal; protein: 17%; total fat: 33%; saturated fat: 11%) containing herbs and spices at 0.5, 3.3, and 6.6 g.d-1.2100 kcal-1 [low-, moderate-, and high-spice diets, respectively (LSD, MSD, and HSD)] in adults at risk for CVD.

Methods: Fifty-four adults (57% female; mean ± SD age: 45 ± 11 y; BMI: 29.8 ± 2.9 kg/m2; waist circumference: 102.8 ± 7.1 cm) were included in this 3-period, randomized, crossover, controlled-feeding study. Each diet was provided for 4 wk with a minimum 2-wk washout period. At baseline and the end of each diet period, participants provided a fecal sample for 16S rRNA gene (V4 region) sequencing. QIIME2 was used for data filtration, sequence clustering, taxonomy assignment, and statistical analysis.

Results: α-diversity assessed by the observed features metric ( P = 0.046) was significantly greater following the MSD as compared with the LSD; no other between-diet differences in α-diversity were detected. Differences in β-diversity were not observed between the diets ( P = 0.45). Compared with baseline, β-diversity differed following all diets ( P < .02). Enrichment of the Ruminococcaceae family was observed following the HSD as compared with the MSD (relative abundance = 22.14%, linear discriminant analysis = 4.22, P = 0.03) and the LSD (relative abundance = 24.90%, linear discriminant analysis = 4.47, P = 0.004).

Conclusions: The addition of herbs and spices to an average American diet induced shifts in gut bacterial composition after 4 wk in adults at risk for CVD. The metabolic implications of these changes merit further investigation. This trial was registered at clinicaltrials.gov as NCT03064932.

Keywords: bacteria; herbs; microbiome; microbiota; polyphenols; spices.

Copyright © 2022 American Society for Nutrition.

Figures

FIGURE 1

α-diversity values at baseline and following each spice-containing diet based on the following metrics: (A) Pielou's evenness, (B) Faith's phylogenetic diversity, and (C) observed features. Values are presented as median (line), IQR (box), 95% CI (error bars), and outliers (circles). Statistical analyses were performed with SAS version 9.4 (SAS Institute). The mixed models procedure (PROC MIXED) was used to determine the effect of diet on each α-diversity metric. When a main effect was detected, post hoc tests were conducted and adjusted for multiple comparisons using the Tukey–Kramer method. Tukey–Kramer adjusted P values are shown. LSD: n = 44; MSD: n = 52; HSD: n = 47. HSD, high-spice diet; LSD, low-spice diet; MSD, moderate-spice diet.

FIGURE 2

β-diversity assessed by principal coordinate analysis plots based on the weighted UniFrac distance metric (A) overall and (B) separated by diet in participants at risk of CVD. LSD: n = 44; MSD: n = 52; HSD: n = 47. CVD, cardiovascular disease; HSD, high-spice diet; LSD, low-spice diet; MSD, moderate-spice diet.

FIGURE 3

LEfSe enrichment plots display significantly (P ≤ 0.05, LDA ≥ 2) enriched taxa following the (A) LSD, (B) MSD, and (C) HSD when compared with baseline in participants at risk of CVD. LDA scores are displayed on the x-axis and quantify the strength of enrichment within each categorical group. LSD: n = 44; MSD: n = 52; HSD: n = 47. CVD, cardiovascular disease; HSD, high-spice diet; LDA, linear discriminant analysis; LEfSe, linear discriminant analysis effect size; LSD, low-spice diet; MSD, moderate-spice diet.