The body’s nitrate sources include both exogenous nitrates from food and endogenous nitrates formed via the oxidation of nitrites and nitric oxide (NO). Exogenous nitrates can be transformed into nitrites by oral bacteria through the digestive tract-salivary gland cycle and are eventually converted into NO in the blood and tissues. Therefore, they are considered important sources of NO in the body. The currently employed methods for loading exogenous nitrates include oral administration of potassium nitrate or sodium nitrate, as well as the ingestion of natural sources such as vegetable juices. In clinical studies, compared with potassium nitrate and sodium nitrate, vegetable juices rich in nitrates, most commonly beetroot juice (BRJ), have been used more widely as nutritional supplements. To meet the needs of clinical studies, manufacturers may isolate nitrates from vegetable juices to serve as a negative control. In this book, natural vegetable juice is presented as a nutritional supplement with nitrates as its main component.