Effects of low and high dietary nitrate intake on human saliva, plasma and skeletal muscle nitrate and nitrite concentrations and their functional consequences

Dietary nitrate (NO₃^-) supplementation has been shown to reduce blood pressure (BP), improve exercise performance, and alter the oral microbiome. Following a "control" diet (CON), we manipulated dietary NO₃^- intake to examine the effect of a short-term (7-day) low NO₃^- diet (LOW) followed by a 3-day high NO₃^- diet (HIGH), compared to a 7-day standard (STD) NO₃^- diet followed by HIGH, on saliva, plasma, and muscle [NO₃^-] and nitrite ([NO₂^-]), BP, and cycling exercise performance in healthy young adults. We also examined the effect of LOW on the oral microbiome. Saliva [NO₃^-] and [NO₂^-], and plasma [NO₃^-] were significantly lower than CON following LOW (all P < 0.05) but there was no change in plasma [NO₂^-] or muscle [NO₃^-] and [NO₂^-] (all P > 0.05). Following HIGH, saliva and plasma [NO₃^-] and [NO₂^-], and muscle [NO₃^-], were significantly elevated above CON, LOW and STD (all P < 0.05), but there was no difference between CON-LOW-HIGH and CON-STD-HIGH (P < 0.05). BP and exercise performance were not altered following LOW (P > 0.05). HIGH significantly reduced systolic and diastolic BP compared to CON when preceded by STD (both P < 0.05) but not when preceded by LOW (P > 0.05). Peak (+4 %) and mean (+3 %) power output during sprint cycling was significantly improved following HIGH (both P < 0.05), with no differences between CON-LOW-HIGH and CON-STD-HIGH (both P > 0.05). LOW altered the oral microbiome composition, including decreases in relative abundances of phylum Proteobacteria and genus Neisseria. The findings indicate that a short-term low NO₃^- diet lowers plasma but not skeletal muscle [NO₃^-]. The maintenance of plasma [NO₂^-] and muscle [NO₃^-] and [NO₂^-] following LOW may be indicative of their importance to biological functions, including BP regulation and exercise performance.