Vegetables, Nitrates, and Nitrites

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Vegetables Guard the Gut ... for a Startling Reason

Nitrites in cured meats can turn cancerous, but prove stomach-protective

when produced from vegetables

by Craig Weatherby

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Have the nitrites in cured meats been unfairly demonized?

Not exactly. But a study from Sweden paints a more nuanced picture of

this widely feared preservative.

Meat processors use sodium nitrite to preserve the red color in cured

meat, and lend it a salty flavor. (In a reaction with meats' myoglobin,

nitrite yields a rich red color.)

Absent added nitrite, hot dogs, bologna, and bacon would look gray.

Sodium nitrate is used in dry cured meat, because it breaks down slowly

into nitrite.

Key Points

- Swedish study shows that the nitrates in vegetables help strengthen

stomach walls by producing nitric oxide in the gut.

- Oral bacteria turn nitrates into nitrites, which convert to nitric

oxide in the stomach.

- Nitric oxide produced from dietary nitrates protects animals' stomachs

from aspirin-induced damage.

- Nitrate-rich vegetables may help keep stomachs healthy, but

anti-bacterial mouthwash may block their benefits.

The real reason may be coloration, but the meat industry justifies its

use of nitrite and nitrate on anti-bacterial grounds. In fact, freezing

and refrigeration work just as well, and the USDA has developed an

alternative method using lactic-acid-producing bacteria.

The nitrites in meat can form cancer-causing chemicals called

nitrosamines, and this happens much more when nitrite-cured meats such

as bacon are cooked.

Because lab evidence raises concern about people - especially children

and prengnant mothers - who might eat a lot of bacon, U.S. companies

must add vitamin C or erythorbate to reduce nitrosamine formation.

Despite dire indications from lab tests, the epidemiological evidence

hasn't shown a convincing link between nitrites or nitrates and cancer

risk (Eichholzer M et al. 1998; Blot WJ et al. 1999).

While the cancer risks associated with red and cured meats may stem as

much from their iron and/or salt content as to nitrites, both foods are

linked strongly to higher colon cancer risk, so it seems wise to

minimize consumption.

We now know that people's oral bacteria convert the nitrates that occur

naturally in common vegetables into nitrites.

And that unexpected fact leads us to today's story.

Human mouths produce nitrites in abundance Some fruits and vegetables

are rich in nitrates, with the levels dependent to some extent on the

amount of nitrogen-containing fertilizer applied to the crops.

Oral bacteria convert nitrates into nitrites, and when we swallow them,

gastric acids convert nitrites into the essential metabolic chemical

nitric oxide.

Nitric oxide can act as an antioxidant, but more important, the body

uses it to keep arteries properly dilated. (Viagra works by raising

nitric oxide levels and thereby easing blood flow to the penis.)

We've long known that nitric oxide is produced by bodily enzymes. But

recently it was discovered that nitric oxide can also be formed in the

stomach from nitrites produced in the saliva, without enzymatic

assistance.

Nitrates in veggies bolster stomachs and block aspirin-induced bleeding

Doctoral candidate sson of Sweden's Uppsala University has

published a study that encourages consumption of nitrate-rich vegetables

such as spinach, lettuce, radishes and beetroot.

Earlier this month, his team published a study demonstrating that

nitrate-rich vegetables strengthen the stomach's mucous membranes.

sson's research shows that when nitric oxide is formed in the

stomach this stimulates protective mechanisms that exist keep the

stomach from digesting itself along with food.

The stomach constantly renews the mucous layer of the mucous membrane

and nitric oxide widens the blood vessels in the mucous membrane, thus

increasing blood flow and aiding regeneration of mucus (sson J et

al. 2007).

Last year, sson's team reported that nitrates in food protected

rats against the gastrointestinal damage associated with chronic use of

aspirin, Aleve, and other non-steroidal anti-inflammatory drugs

(NSAIDs).

Gastric bleeding kills tens of thousands of aspirin users annually by

causing undiagnosed bleeding and ulcers in the gastrointestinal tract.

The key finding by sson is that oral bacteria are vital to

supplying nitrates that yield the nitric oxide needed to strengthen the

stomach's mucous membrane.

As he wrote, " We demonstrated that a nitrate-rich diet protects against

NSAID-induced gastric damage, as a result of the increased formation of

NO in the stomach. We also showed that the gastro-protective effect

attributed to nitrate depended completely on conversion of nitrate to

nitrite by the bacterial flora colonizing the tongue, and that the oral

microflora is therefore important in regulating physiological conditions

in the stomach. "

The fact that oral bacteria indirectly support gastrointestinal health

was revealed last year by a study that sson and colleagues

conducted in rats.

The Swedes fed rats a nitrate-rich chow, along with aspirin-type

anti-inflammatory drugs. But only the animals that also received an

antibacterial oral spray suffered damage to their mucous membrane.

(Jansson EA et al. 2007)

The oral spray had killed the animals' oral bacteria, which otherwise

would have converted the dietary nitrates into nitrites, to be converted

to nitric oxide in their stomachs.

As sson said, " This shows how important our oral flora [microbes]

is. It is an important issue, as antibacterial mouthwashes have become

more and more common. If a mouthwash eliminates the bacterial flora in

the mouth this may be important to the normal functioning of the

stomach, as the protective levels of nitric oxide greatly decrease. "

He also thinks that his team's results provide another important reason

to enjoy fruits and vegetables in abundance: " If we followed the Swedish

Food Administration's recommendation and ate 500 g (18 ounces) of fruit

and vegetables per day it would definitely be better for our stomachs. "

In addition to their contribution to nitric oxide production in the

stomach, prior evidence suggests that the antioxidants in fruits,

vegetables, whole grains, and tea may help protect the gastrointestinal

tract from free radicals.

Free radicals can damage DNA and thereby promote cancer, so food-borne

antioxidants could help delay or deter the development of stomach, colon

and rectal cancer.

Sources

- Bjorne HH, sson J, on M, Weitzberg E, Holm L, Lundberg

JO. Nitrite in saliva increases gastric mucosal blood flow and mucus

thickness. J Clin Invest. 2004 Jan;113(1):106-14. Erratum in: J Clin

Invest. 2004 Feb;113(3):490.

- Blot WJ, BE, Boice JD Jr. Childhood cancer in relation to

cured meat intake: review of the epidemiological evidence. Nutr Cancer.

1999;34(1):111-8. Review.

- Eichholzer M, Gutzwiller F. Dietary nitrates, nitrites, and N-nitroso

compounds and cancer risk: a review of the epidemiologic evidence. Nutr

Rev. 1998 Apr;56(4 Pt 1):95-105. Review.

- Jansson EA, sson J, Reinders C, Sobko T, Bjorne H, on M,

Weitzberg E, Holm L, Lundberg JO. Protection from nonsteroidal

anti-inflammatory drug (NSAID)-induced gastric ulcers by dietary

nitrate. Free Radic Biol Med. 2007 Feb 15;42(4):510-8. Epub 2006 Nov 21.

- sson J, on M, Jansson EA, Patzak A, Lundberg JO, Holm L.

Dietary nitrate increases gastric mucosal blood flow and mucosal

defense. Am J Physiol Gastrointest Liver Physiol. 2007

Mar;292(3):G718-24. Epub 2006 Nov 2.

- sson J. Nitrate, Nitrite and Nitric Oxide in Gastric Mucosal

Defense. ISBN: 978-91-554-7152-1

- Uppsala University (UU). Nitrates in vegetables protect against

gastric ulcers. May 7, 2008. Accessed online May 11, 2008 at

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