By Gabe Mirkin, M.D.
Nitrates from the foods you eat can be converted in your body to nitric oxide, which widens blood vessels to increase blood flow throughout your body, to improve exercise tolerance and to help prevent heart disease (Med Sci Sports Exerc, Feb 1, 2021;53(2):280-294; Scand J Med Sci Sports, Oct 1, 2012) and to lower high blood pressure (Nitric Oxide, Nov 1, 2018;80:37-44; Hypertension, 2010;56:274-81). Doctors prescribe nitrates to treat angina to increase blood flow to the heart. Older people, in particular, should increase their intake of nitrate-rich vegetables, since aging decreases the body’s ability to make nitric oxide.
Population studies have repeatedly shown us that vegetable-rich diets are associated with reduced risk for high blood pressure, strokes and heart attacks (Am J Clin Nutr, 2013;98:1514-1523), and many other diseases (J Am Heart Assoc, July 2016;5(7):e003402). In particular, leafy green vegetables appear to be the foods that offer the most protection against strokes and heart attacks (Ann Intern Med, 2001;134:1106-1114) and leafy green vegetables are the foods that are among the highest dietary sources of nitrates (Am J Clin Nutr, 2009;90:1-10). The best vegetable sources of nitrates are those in which you eat the leaves, stems or roots: celery, lettuce, radishes, beets, spinach, broccoli, Chinese cabbage, onions, endive, kohlrabi, leeks, parsley, carrots, and so forth (Am J Clin Nutr, 2009 Jul;90(1):1-10).
You Don’t Need Beet Root Juice
Some bicycle racers drink beet root juice because a study showed that beet root juice before a time trial helped racers go 2.8 percent faster over both 4K and 16K courses (Med Sci Sports Exerc, June 2011). Beet root juice contains nitrates and the dose of nitrates used in the study (6.2 mmol) was 4-12 times greater than what the average person takes in each day. Nitrates have been shown to reduce the oxygen cost of cycling (J Appl Physiol, 2009;107:1144-55), increase power of knee extensor exercise (J Appl Physiol, 2010;109:135-48), and help athletes run faster (J Appl Physiol, 2011;110:591-600). However, athletes can get their nitrates just by eating lots of vegetables (Med Sci Sports Exerc, 2014;47:1643-1651); beet root juice does not have any special benefits.
Why Nitrates in Meat May Be Harmful
Additives such as sodium nitrate are used to preserve meats and give them their pink color, and nitrates in processed meats have been associated with increased risk for heart attacks and certain cancers. Nitrates are known to help suppress the growth of harmful bacteria but they have also been linked to potential cancer-causing effects. Nitrates are relatively inert and do not react with chemicals around them, but nitrates can be converted by bacteria in the mouth to nitrites, which pass to the stomach where the strong stomach acids convert nitrites to known chemical carcinogens called nitrosamines. This occurs abundantly only when there is a rich source of ammonia and other amines found in high-protein foods, such as meat, fish and chicken.
So while the nitrates in vegetables are healthful, nitrates in meats may be harmful. Cooking meats at high temperatures also creates nitrosamines. The potential link between cancers and nitrates, nitrites or nitrosamines from meats is controversial, and has been seen only with eating meat daily; occasional meat eating has not been associated with increased risk for cancer.
Do Not Take Nitrate Pills or Drink Stale Cooking Liquids
Excessive nitrites can accumulate and prevent oxygen from attaching to red blood cells. This rare condition, called methemoglobinemia, can prevent you from even being able to move and can be fatal. This condition could be caused by taking nitrate pills or by drinking very large amounts of stale juice from cooked spinach or other vegetables high in nitrates that have not been refrigerated. Boiling vegetables reduces nitrate content (Toxicol Lett, 2008(Oct 1);181(3):177-81), but bacteria in old, stale vegetable juices can convert the healthful nitrates to the potentially-harmful nitrites.
Fresh vegetables are usually resistant to bacterial infections, but once a vegetable is cooked, bacteria can multiply in the cooking liquid. Refrigerate leftover cooked vegetables and eat them within a few days. Freezing inactivates bacteria, so commercially frozen cooked vegetables should have low levels of nitrites. You can also freeze your own cooked leftover vegetables.
If you want to get all of the benefits from the right kinds of nitrates, eat a widely varied diet with at least five servings a day of vegetables and fruits. Read the list of ingredients on processed meats and other processed foods, and limit or avoid those that list additives such as “sodium nitrate.”