Are greens always good?
Kayley asks: Do reheated green vegetables lead to cancer?
Wynnie says: Green leafy vegetables contain high concentrations of compounds called nitrates. Nitrate is used as a fertiliser in many countries. The amount of nitrates in vegetables depends on the type, and the season, soil and water conditions in which they've been grown.
Nitrate in itself is harmless, but can be converted to compounds called nitrites, and then to nitrosamines, which are potent carcinogens. Bacteria contains enzymes that convert nitrates to nitrites. This is known to happen in chopped, bagged spinach when it is heated, stored and then reheated. Although nitrites are also harmless, health experts recommend that babies should avoid them since nitrites can adversely affect the absorption of oxygen from the blood.
It is thought that nitrosamines might be produced from nitrates/nitrites (and amines - breakdown products from protein) during the digestion of foods in the stomach where there is a source of nitrate/nitrite. This has led to the recommendation that reheating green vegetables is to be avoided. But more recent studies have shown that the concentrations of nitrosamines aren't as high as it was once assumed, and so it's now not considered as dangerous to eat reheated green veggies.
Remember, though, that reheating vegetables can lead to further loss of water-soluble vitamins, such as C and B, which are especially sensitive to heat, air and light.
What other foods contain nitrates, nitrites and nitrosamines?
Many processed foods, especially cured meats such as bacon, hot dogs, sausages, ham and other cold cuts, contain nitrates as a preservative to maintain colour and microbial safety. Nitrites are used as additives when meat is cured; they slow down the development of the dangerous botulinum toxin.
Some processed meats and certain fungi (eg ceps) have been shown to contain varying amounts of carcinogenic nitrosamines. Overcooking meat products cured with nitrite, such as burning bacon, can be dangerous. Microwaving bacon produces less nitrosamines than frying it.
Are nitrosamines really dangerous?
Scientific studies have shown that nitrosamines can cause stomach cancer in laboratory animals. Research has found a much higher risk of stomach cancer in people that eat a lot of red meat and preserved meats, such as bacon and sausages. A diet high in very salty foods also increases the risk of stomach cancer.
Bottom line
If you want to avoid nitrates, nitrites and nitrosamines, choose fresh, unprocessed foods wherever possible. Organically grown vegetables contain fewer nitrates than their non-organic counterparts. Avoid or cut down on cured and processed meats as much as possible, and don't overcook meat products cured with nitrites.
When you do eat foods containing nitrites, have a glass of orange juice, or other vitamin C-rich foods such as green peppers, tomato juice, broccoli, oranges, strawberries, kiwis or mangos, as well. Vitamin C inhibits the conversion of nitrites to nitrosamines in your stomach.
