Abstract
The presence of nitrates and nitrites in food is associated with an increased risk of gastrointestinal cancer and, in infants, methemoglobinemia. Despite the physiologic roles for nitrate and nitrite in vascular and immune function, consideration of food sources of nitrates and nitrites as healthful dietary components has received little attention. Approximately 80% of dietary nitrates are derived from vegetable consumption; sources of nitrites include vegetables, fruit, and processed meats. Nitrites are produced endogenously through the oxidation of nitric oxide and through a reduction of nitrate by commensal bacteria in the mouth and gastrointestinal tract. As such, the dietary provision of nitrates and nitrites from vegetables and fruit may contribute to the blood pressure-lowering effects of the Dietary Approaches to Stop Hypertension (DASH) diet. We quantified nitrate and nitrite concentrations by HPLC in a convenience sample of foods. Incorporating these values into 2 hypothetical dietary patterns that emphasize high-nitrate or low-nitrate vegetable and fruit choices based on the DASH diet, we found that nitrate concentrations in these 2 patterns vary from 174 to 1222 mg. The hypothetical high-nitrate DASH diet pattern exceeds the World Health Organization’s Acceptable Daily Intake for nitrate by 550% for a 60-kg adult. These data call into question the rationale for recommendations to limit nitrate and nitrite consumption from plant foods; a comprehensive reevaluation of the health effects of food sources of nitrates and nitrites is appropriate. The strength of the evidence linking the consumption of nitrate- and nitrite-containing plant foods to beneficial health effects supports the consideration of these compounds as nutrients.
Generated Summary
This journal article investigates the physiological context of nitrates and nitrites, focusing on their potential health benefits derived from dietary sources. The study explores the roles of nitrates and nitrites in vascular and immune function, emphasizing that approximately 80% of dietary nitrates come from vegetable consumption, with nitrites sourced from vegetables, fruits, and processed meats. The research uses a convenience sample of foods to quantify nitrate and nitrite concentrations, incorporating these values into hypothetical dietary patterns based on the DASH diet. The methodology involves comparing high-nitrate and low-nitrate DASH diet patterns to assess their impact on nitrate intake, questioning recommendations to limit nitrate and nitrite consumption from plant foods. The study’s scope includes analyzing the evidence linking plant-based nitrate and nitrite consumption to health benefits, advocating for a reevaluation of their effects and their consideration as nutrients.
Key Findings & Statistics
- Approximately 80% of dietary nitrates are derived from vegetable consumption.
- Nitrite sources include vegetables, fruit, and processed meats.
- The study found that nitrate concentrations in two hypothetical DASH diet patterns varied from 174 to 1222 mg.
- The hypothetical high-nitrate DASH diet pattern exceeds the World Health Organization’s Acceptable Daily Intake for nitrate by 550% for a 60-kg adult.
- In the European Union, nitrate intakes from vegetables constitute more than half of the recommended intake of 400 g, and actual nitrate intakes would be approximately 81-106 mg/d before additional nitrate losses from washing, peeling, and/or cooking are taken into consideration.
- In the United States and Europe, international estimates of nitrate intakes from food are 31-185 mg/d in Europe and ≈40–100 mg/d in the United States.
- Nitrite intakes vary from 0 to 20 mg/d.
- Mean nitrate and nitrite contents of fruit and vegetables from a convenience sample:
- Apple sauce: nitrate 0.3 mg/100g, nitrite 0.008 mg/100g
- Banana: nitrate 4.5 mg/100g, nitrite 0.009 mg/100g
- Fruit mix: nitrate 0.9 mg/100g, nitrite 0.08 mg/100g
- Oranges: nitrate 0.8 mg/100g, nitrite 0.02 mg/100g
- Broccoli: nitrate 39.5 mg/100g, nitrite 0.07 mg/100g
- Carrots: nitrate 0.1 mg/100g, nitrite 0.006 mg/100g
- Cole slaw: nitrate 55.9 mg/100g, nitrite 0.07 mg/100g
- Ketchup: nitrate 2.0 mg/100g, nitrite 0.17 mg/100g
- Mustard greens: nitrate 116.0 mg/100g, nitrite 0.003 mg/100g
- Salad mix: nitrate 82.1 mg/100g, nitrite 0.13 mg/100g
- Spinach: nitrate 741 mg/100g, nitrite 0.02 mg/100g
- Tomato: nitrate 39.2 mg/100g, nitrite 0.03 mg/100g
- Vegetable soup: nitrate 20.9 mg/100g, nitrite 0.001 mg/100g
- Desiccated vegetable dietary supplement: nitrate 27,890 mg/100g, nitrite 10.5 mg/100g
- Bacon: nitrate 5.5 mg/100g, nitrite 0.38 mg/100g
- Bacon, nitrite-free: nitrate 3.0 mg/100g, nitrite 0.68 mg/100g
- Ham: nitrate 0.9 mg/100g, nitrite 0.89 mg/100g
- Hot dog: nitrate 9.0 mg/100g, nitrite 0.05 mg/100g
- Pork tenderloin: nitrate 3.3 mg/100g, nitrite 0 mg/100g
- The high-nitrate DASH diet would result in the consumption of 1222 mg nitrate and 0.351 mg nitrite compared with the low-nitrate DASH diet that yields 174 mg nitrate and 0.41 mg nitrite.
- The WHO ADI for nitrate (0–3.7 mg/kg) translates into an equivalent of 222 mg nitrate for a 60-kg adult.
Other Important Findings
- The presence of nitrates and nitrites in food is associated with an increased risk of gastrointestinal cancer and, in infants, methemoglobinemia.
- Dietary nitrates are essentially inert and acquire biological activity only after reduction to nitrite.
- Dietary provision of nitrates and nitrites from vegetables and fruit may contribute to the blood pressure-lowering effects of the Dietary Approaches to Stop Hypertension (DASH) diet.
- Nitrite is produced endogenously through the oxidation of nitric oxide and through a reduction of nitrate by commensal bacteria in the mouth and gastrointestinal tract.
- The health benefits of vegetables and fruit may derive from the contribution of their constituents to food patterns such as the Mediterranean-type pattern.
- Recent prospective epidemiologic studies have shown that green leafy vegetables are among the foods most protective against coronary heart disease and ischemic stroke risk.
- The Dietary Approaches to Stop Hypertension (DASH) studies found that diets rich in vegetables (ie, 8–10 servings) and low-fat dairy products can lower blood pressure.
- The blood pressure-lowering effect of this diet was hypothesized to be attributable to the high calcium, potassium, polyphenols, and fiber contents and low sodium and animal protein contents.
- Inorganic nitrate (NO3¯) in certain vegetables and fruit can provide a physiologic substrate for reduction to nitrite (NO2), nitric oxide, and other metabolic products (NOx) that produce vasodilation, decrease blood pressure, and support cardiovascular function.
- Nitrite can directly induce vasodilation in hypoxic endothelium.
- Unlike the provision of eNOS-derived nitric oxide to the endothelium to maintain vasomotor tone, nitric oxide production from nitrite occurs primarily in tissues.
- The stepwise reduction of nitrate to nitrite to nitric oxide is an inefficient process.
- Dietary sources of nitrate and nitrite may bolster the reserve of these compounds for optimal functioning through periods of physiologic stress and diseases characterized by endothelial dysfunction.
- The nitrate content of organic vegetables may be less than that of vegetables grown in the presence of nitrogen-containing fertilizers.
- In terms of plant anatomy, the nitrate content of vegetable organs can be listed in descending order (most to least) as petiole > leaf > stem > root > influorescence > tuber > bulb > fruit > seed.
- The mean intake estimates for nitrate and nitrite in the United States and Europe vary by investigator but are consistent and comparable.
- The bioavailability of dietary nitrate is 100%.
- Consumption of red and processed meats is associated with an increased risk of certain types of cancer.
- The association between nitrite consumption and gastrointestinal cancers was bolstered by findings that ingested nitrites may react with secondary amines or N-alkylamides to generate carcinogenic N-nitroso compounds (NOCs).
Limitations Noted in the Document
- The study acknowledges that a simple characterization of an optimal concentration of dietary nitrate and nitrite based on an overall picture of the nitrate and nitrite economy is not possible.
- Nitrate and nitrite balance studies are not, at present, feasible.
- The study notes that the data on nitrate and nitrite contents of vegetables and fruit bolster the strength of existing evidence to recommend their consumption for health benefits; however, it also acknowledges that these measurements may differ from samples from more disparate geographic locations.
- The authors recognize that the research is limited by the lack of causal inference with regard to the etiologic roles of dietary nitrates and nitrites in methemoglobinemia and cancer.
- The wide variation in nitrate and nitrite contents of vegetables, fruit, and their juices make it difficult to translate the oft-quoted dietary recommendation “Eat your fruits and vegetables” into high nitrate and nitrite intake levels.
- The potential health risks of excessive nitrate and nitrite exposure are discussed, but the study notes that the few human nitrate and nitrite exposure studies, including children and adults, have not produced methemoglobinemia.
- The study acknowledges that the biologically plausible hypothesis of nitrite toxicity has essentially transformed a plausible hypothesis into sacrosanct dogma.
- The study does not delineate if the N and N from fruits and veggies is different than the N and N added to processed meat – could be different molecules.
Conclusion
In conclusion, this research comprehensively examines the physiological context of dietary nitrates and nitrites, highlighting their potential health benefits derived from plant-based sources. The study employs a detailed methodological approach, including a thorough assessment of the nitrate and nitrite content in common food items and the application of these values within different dietary scenarios. The findings underscore the wide variation in nitrate and nitrite concentrations within vegetables, fruits, and their juices, cautioning against simplistic dietary recommendations. The study’s detailed analysis provides compelling evidence to support the notion that dietary nitrates and nitrites, especially from plant sources, play essential roles in supporting cardiovascular health and gastrointestinal immune function. This positions these compounds as potential nutrients, contradicting current regulatory limits and encouraging further investigation into their comprehensive biological effects. The data emphasizes that because of the wide variation in nitrate and nitrite contents of vegetables, fruits, and their juices, practicing the oft-quoted dietary recommendation “Eat your fruits and vegetables” may not translate into high nitrate and nitrite concentrations in the diet. Furthermore, the evidence suggests that normal physiological exposure levels of nitrite and nitrate greatly exceed concentrations considered to produce health risks, questioning the rationale supporting the current regulatory limits. This reevaluation suggests that food sources of nitrates and nitrites should be considered as nutrients, as the benefits of vegetable and fruit consumption outweigh any perceived risks of cancer from the consumption of nitrate and nitrite in these foods. The study’s findings support the conclusions of the European Food Safety Authority that benefits of vegetable and fruit consumption outweigh any perceived cancer risk from the consumption of nitrate and nitrite in these foods.