Processed red meat has been investigated for its high nitrate and nitrite concentrations (nitrate is the oxidised form of nitrite and both are added to various sorts of processed meats as preservatives). Nitrates and nitrites can be converted to nitrosamines through reactions with secondary amines in the gut under acidic conditions. These nitrosamines may have detrimental effects of cell regulation, and may be a cause of gut cancer. Overall the synthetic nitrates and nitrites added to meat as a preservative are therefore thought to be detrimental to long term health. However, processed meats are not the only source of nitrates and nitrites in the diet of humans. Plants naturally produce nitrates and nitrites as part of their metabolism, and the health effects of these compounds has been investigated. For example, in one study researchers fed healthy subjects a drink containing either sodium nitrate, concentrated beetroot juice, a rocket salad beverage, or a spinach beverage. Each of these drink supplied 800 mg of nitrates.
Plant foods contain nitrates that may cause a decrease in blood pressure following consumption. However, plants are also rich in antioxidants, and antioxidants have also been shown to lower blood pressure. It is through that nitrates cause a lowering of blood pressure because they increase the availability of nitric oxide through the reverse pathway via conversion of nitrite and nitrate to nitric oxide. Nitric oxide is an important signal molecule that causes the dilation of blood vessels, thus lowering blood pressure. However, antioxidants can also increase nitric oxide production. However, they do this is a different way. Free radicals inhibit nitric oxide synthase, the enzyme responsible for the generation of nitric oxide in blood vessels. Antioxidants can prevent this inhibition through the quenching of free radicals, and this increase the generation of nitric oxide indirectly. Therefore the blood pressure lowering effects of plant foods may come from multiple mechanisms, centred on the generation of nitric oxide in blood vessels.
The results of the study showed that following consumption of the drinks, plasma nitrates increased significantly in all treatments to a similar extent. However, differences in plasma nitrite concentrations existed between the different drinks. Sodium nitrate and beetroot juice produced increases in plasma nitrite of 580 and 557 nmol/ L, respectively. However, rocket salad and spinach increased plasma nitrite concentrations by 643 and 980 nmol/L, respectively. The systolic blood pressure decreased significantly by 5 and 6 mmHg at 150 min following beetroot and rocket drinks, and by 7 mmHg at 300 min following the spinach drink. Diastolic pressure was lowered after all drinks, but remained depressed for longer following rocket and spinach drinks. Therefore, evidence suggests that the consumption of plant based drink may reduce blood pressure significantly, and this blood pressure decrease is associated with a rise in plasma nitrite and nitrate concentrations. Spinach and rocket salad may be particularly efficient in this role.
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