The effects of inorganic nitrate and inulin co-ingestion on circulating metabolites and blood pressure in young adults: a pilot double-blind randomised crossover trial

Dietary patterns enriched in fermentable fibre (such as inulin) and inorganic nitrate are linked to cardiovascular benefits, possibly mediated by gut microbiota-derived bioactive compounds including short-chain fatty acids (SCFAs) and nitric oxide (NO). However, the potential synergistic effects remain unclear. We conducted a randomised, double-blind, crossover study to investigate the acute effects of inulin (15 g; INU), nitrate (400 mg; NO₃ ^-), and their combination (INU + NO₃ ^-) on plasma nitrate and nitrite levels, SCFAs, and blood pressure (BP) in 20 adults. Plasma nitrate and nitrite were significantly elevated following INU + NO₃ ^- and NO₃ ^- compared to INU (<i>p</i> < 0.001). Plasma SCFAs were increased after INU + NO₃ ^- and INU, but the incremental AUC was not statistically significant, likely due to large inter-individual variability. No significant main effects were observed on BP; however, inverse correlations were identified between peak plasma nitrite and diastolic BP (r_s = -0.61, <i>p</i> = 0.004) and mean arterial pressure (MAP) (r_s = -0.59, <i>p</i> = 0.005) following INU + NO₃ ^-. Peak nitrate concentrations were inversely correlated with diastolic BP following NO₃ ^- (r_s = -0.47, <i>p</i> = 0.004). Co-supplementation with inulin and nitrate did not enhance plasma nitrate/nitrite or BP beyond nitrate alone but modulated SCFA profiles, suggesting potential interactions between fibre fermentation and nitrate metabolism for cardiovascular health.