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

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.