DEAR DR. BLONZ: How dangerous are the nitrates that are in hot dogs, ham, sausages and deli meats? How do they differ from those found in vegetables? Are they all carcinogens that have to be actively avoided to reduce the risk of cancer? -- F.G., Berkeley, Calif.
DEAR F.G.: Your question involves both nitrates and nitrites; the two are related, but there are important differences.
Nitrites: Food processors use nitrites as preservatives in cured and smoked meat products such as bacon, sausage, smoked and deli meats. These are all meats that tend to be stored under refrigeration for a number of days, and without an appropriate preservative such as sodium nitrite, there's a relatively high risk of botulism -- an often-fatal food poisoning. Nitrites, themselves, represent a risk as they can form cancer-causing chemicals called nitrosamines. These compounds can form when a nitrite (either sodium nitrite or potassium nitrite) reacts with protein at a high cooking temperature. The principle here is that with the exception of freezing or high-temperature cooking, there's no safe way to protect against botulism in a low-acid food such as a cured meat.
Nitrates: Nitrates occur naturally in several vegetables including turnip greens, beets, celery, rhubarb, spinach, radish, parsley and lettuce. They represent less of a risk than nitrites, but a nitrate can be converted to a nitrite in the stomach. This means that nitrosamines can theoretically form in the stomach when you eat a nitrate-containing vegetable and a protein food at the same meal. The important difference is that antioxidant nutrients can help limit nitrosamine formation, and these nutrients, such as vitamin C, E or antioxidant phytochemicals, tend to be found in nitrate-containing foods.
By contrast, in cured meat products such as bacon or sausage, all the ingredients needed to form nitrosamines are in the same package and the nitrosamines can be formed before you eat. In weighing the relative risk from botulism against the presence of the nitrite preservative, scientists decided that if you're going to eat cured or smoked meats, the use of nitrate preservatives is an acceptable risk.
Because there is some risk involved, nitrite preservatives are not permitted in baby foods.
Although most smoked and cured meats contain sodium or potassium nitrite, you can find nitrite-free meat products either as locally made, short shelf-life products, or in the freezer case where the low temperature can effectively inhibit bacterial growth.
A prudent approach is to limit your intake of nitrite-containing cured and smoked meats. If you enjoy these foods, see if a nitrite-free brand is available. You could also look for a product that contains sodium ascorbate (a salt of vitamin C), sodium erythorbate or vitamin E; these antioxidants can help limit nitrosamine formation. Another option is to make sure you have antioxidant-rich foods at the same meal as the nitrite-containing meats. A salad with the meal, some peppers or vegetables on the sandwich, and fruits as dessert are all additions that could help blunt the potential risk.
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