A few weeks back, I received a call from a hopeful patient asking for confirmation of a nightly news story -- one claiming that bacon might be good for the heart because of the nitrite and nitrate it contains.
Sounds surprising? After all, cured meats are often shunned over concerns that nitrite and nitrate, added to retain color and inhibit the growth of the bacteria that cause botulism, may form potentially carcinogenic compounds called nitrosamines.
The story stemmed from a report published online in the Proceedings of the National Academy of Sciences. Researchers at the University of Texas Health Science Center in Houston studied mice consuming either a nitrate/nitrite-deficient diet or one high in nitrate and nitrite to study effects on the heart after a simulated heart attack. (A third group of mice consumed a regular diet as a control.)
The mice receiving extra nitrate and nitrite in their drinking water had 48% less heart cell death than mice on the regular diet, while mice fed the low nitrate/nitrite diet had 59% greater injury than the controls And 77% of the animals receiving extra nitrate/nitrite survived the heart attack, compared with 58% that were nitrate/nitrite-deficient.
The researchers proposed that the benefit from the enriched water might be the stimulation of nitric oxide production in the body. Nitric oxide, produced in cells lining the surface of the blood vessels, is a gas that dilates arteries, thus aiding blood flow and reducing blood pressure. When inadequate nitric oxide is available, the risk rises for heart disease and stroke.
Nitric oxide is generated from oxygen and an amino acid, arginine, but can also be produced from dietary nitrate by other pathways. Unbeknownst to most people, the majority of the nitrate we consume -- between 70% and 85% -- comes from vegetables and fruits, the richest sources being spinach, lettuce, celery, cauliflower, grapes, strawberries and root vegetables. (Vegetarians may consume up to 10 times the nitrate levels that omnivores do.)
Only about 5% of the nitrate we eat comes from bacon, ham and other cured meats. The rest comes from nitrate naturally present in drinking water.
Once nitrate is absorbed by the small intestine, as much as 25% is taken up from the bloodstream by the salivary glands, where it is concentrated tenfold to twentyfold. Bacteria in the mouth then convert the nitrate to nitrite, and further enzymatic activity in blood and tissues leads to the production of nitric oxide.
Although nitrate and nitrite are not carcinogenic -- in fruits and vegetables, in fact, they act as antioxidants -- during digestion or cooking, nitrite can combine with naturally occurring amines in foods, forming nitrosamines. Some nitrosamines have been shown to be carcinogenic when administered to animals.
But it's unclear, given the nitrate content of the typical human diet, if nitrosamines can be formed in the stomach in large enough doses to induce cancer. In fact, there is some compelling evidence that this is unlikely: Studies of human populations indicate that a diet rich in fruits and vegetables protects against several forms of cancer, particularly gastric cancer.
From an evolutionary standpoint, it doesn't seem plausible that Mother Nature would have purposely allowed secretion of concentrated nitrate in the mouth if it were harmful to us. But that doesn't mean that bacon is the new health food.
Even if cured meats might add a bit of nitrate or nitrite to our day's intake, there is often a fair amount of fat and sodium tagging along.
What's more, fruits and vegetables are naturally rich in vitamin C, which inhibits nitrosamine formation as well as enhances the generation of nitric oxide from nitrite.
I am sure my patient was disappointed, but I told him that we were designed to consume our nitrate in more natural ways -- packaged with vitamins, minerals, antioxidants and phytochemicals in a multitude of healthful vegetables and fruits.
Susan Bowerman is a registered dietitian and assistant director of the UCLA Center for Human Nutrition.