Nitric oxide (NO) is synthesized not only from L-arginine by NO synthases (NOSs), but also from its inert metabolites, nitrite and nitrate. Green leafy vegetables are abundant in nitrate, however whether or not a deficiency in dietary nitrite/nitrate spontaneously causes disease remains to be clarified. In this study, we tested our hypothesis that long-term dietary nitrite/nitrate deficiency induces metabolic syndrome (MetS) in mice. To this end, we prepared a low nitrite/nitrate diet (LND) consisting of an amino acid-based low nitrite/nitrate chow in which the contents of L-arginine, fat, carbohydrates, protein, and energy were identical with a regular chow, and potable ultrapure water. Nitrite and nitrate were undetectable in both the chow and the water. Intriguingly, in comparison with a regular diet, 3 months of the LND significantly elicited visceral adiposity, dyslipidaemia, and glucose intolerance; 18 months of the LND significantly provoked increased body weight, hypertension, insulin resistance, and impaired endothelium-dependent relaxations to acetylcholine; and 22 months of the LND significantly led to death due to cardiovascular disease, including acute myocardial infarction. These abnormalities were reversed by simultaneous treatment with sodium nitrate, and were significantly associated with endothelial NOS down-regulation, adiponectin insufficiency, and gut microbiota dysbiosis. These results provide the first evidence that long-term dietary nitrite/nitrate deficiency gives rise to MetS, endothelial dysfunction, and cardiovascular death in mice, indicating a novel pathogenetic role of the exogenous NO production system in MetS and its vascular complications.