Influence of Chronic Dietary Nitrate on Downstream Atherogenic Metabolites and the Enteral Microbiome—A Double-Blind Randomized Controlled Trial

Background: Inorganic nitrate is abundant in leafy green vegetables and has been shown to exert positive cardiovascular effects through nitric oxide-related pathways. The enteral microbiome is an emerging key player in cardiovascular diseases and depends on dietary habits. Whether dietary inorganic nitrate impacts on the microbiome and atherosclerosis-associated microbiome-dependent metabolites like short chain fatty acids (SCFA) and trimethylamine N-oxide (TMAO) is unknown. Methods: In a double-blind randomized controlled trial, 30 healthy volunteers were included who either received dietary nitrate (0.12 mmol/kg bodyweight) or placebo (equimolar amounts of sodium chloride) for 30 days. The microbiome metabolites TMAO and SCFA were analyzed. The enteral microbiome was analyzed by 16S-rRNA sequencing at baseline and follow-up. Results: Systolic blood pressure decreased after nitrate supplementation (baseline 124.73 mmHg vs. follow up 120 mmHg, p < 0.05) with no change in controls. Dietary nitrate supplementation increased TMAO levels (nitrate baseline 349.28 μ/L vs. nitrate follow-up 481.15 μ/L, p < 0.05), while SCFA levels remained unchanged. The relative abundance of Akkermansia and taxa of Clostridiales were higher in individuals with high compared to normal TMAO levels after nitrate supplementation, while Shannon diversity, richness and evenness did not differ between both groups. Conclusions: Our results indicate that dietary nitrate supplementation is associated with alterations to the enteral microbiome with an impact on proatherogenic metabolites. Further work is warranted to investigate the causal relationship between dietary nutrients, the microbiome and downstream metabolites.