Why are nitrates bad in meat but appear to be good in fruits or vegetables?
Nitrites (in combination with nitrates that become reduced to nitrites) have been added to meat products such as bacon, hams, and salamis for ages. They inhibited some bacterial growth (long before anyone thought of refrigerators), and added a distinctive taste. In recent years we have found that the amino acids in the protein can combine with nitrites to create a family of nitroso compounds, mainly nitrosamines, many of which have an association with cancer. The nitrosamines can form in the cooking process (that’s why bacon, which still has to be cooked, has a different nitrate/nitrite formulation to ham and salami that are not generally heated before eating), or in the stomach.
So what about nitrates in plants? Plants have nitrates naturally occurring in their structure, and often the concentration of nitrates from plant foods far exceeds that in meats. Yet this source of nitrate does not appear to be associated with tumor formation. The reason now appears related to the presence of ascorbic acid (vitamin C) naturally present in the plant leaf and juices. In the presence of ascorbic acid, nitrosamine formation is prevented. Lettuce, peppers, tomatoes, green leafy vegetables, citrus fruits, even raw root vegetables, all contain ascorbic acid, and this appears to protect against nitrosamine formation.
The take-home message? … To increase your safety margin, always include some foods containing ascorbic acid when you eat nitrite-preserved meats. This could be orange juice with your breakfast bacon, lots of lettuce with your ham sandwich, tomato or sauerkraut with your salami on rye, or a vit-C tab at the same time as any of these.
As a footnote, you may have seen packages of hams, salamis, bologna, bacon, mortadella, and a wide range of pickled and preserved meats that LOOK as if they contain nitrates (because of the pink colour). However, the label declares the ingredients to be completely free of nitrates or nitrites. Look closer, do you see "celery extract"? That's the source of the same quantity of nitrates: it's naturally occurring in vegetables such as celery. It's there in abundance.