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 (NO) 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 NO intake to examine the effect of a short-term (7-day) low NO diet (LOW) followed by a 3-day high NO diet (HIGH), compared to a 7-day standard (STD) NO diet followed by HIGH, on saliva, plasma, and muscle [NO] and nitrite ([NO]), BP, and cycling exercise performance in healthy young adults. We also examined the effect of LOW on the oral microbiome. Saliva [NO] and [NO], and plasma [NO] were significantly lower than CON following LOW (all P < 0.05) but there was no change in plasma [NO] or muscle [NO] and [NO] (all P > 0.05). Following HIGH, saliva and plasma [NO] and [NO], and muscle [NO], 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 NO diet lowers plasma but not skeletal muscle [NO]. The maintenance of plasma [NO] and muscle [NO] and [NO] following LOW may be indicative of their importance to biological functions, including BP regulation and exercise performance.