Vegetables of the brassica family include broccoli, brussel sprouts, kale, cabbage, watercress, and cauliflower. These vegetables contain anti-cancer chemicals called glucosinolates. Studies show that high intakes of brassica family vegetables are protective of cancer, particularly cancer of the gastrointestinal tract. This is because glucosinolates may protect from the cancer effects of nitrosamines, which are formed from nitrates and nitrites in processed meat.
Glucosinolates are sulphur containing molecules in brassica vegetables. High intakes of glucosinolates may protect from cancer, but the glucosinolates do not actually have beneficial effects themselves. To be beneficial, the glucosinolates must first be converted into other chemicals called isothiocyanates and indoles. It is these products of the glucosinolates that are actually beneficial against cancer.
Brassica Vegetables And Detoxification
Isothiocyanates and indoles may decrease the risk of cancer because they decrease phase I detoxification, a process in the body that activates many chemical compounds to become more damaging. At the same time the isothiocyanates and indoles induce phase II detoxification, which rapidly converts the more potent cancer chemicals to harmless substances ready for excretion. This effect reduces the exposure of the body to carcinogenic compounds.
Glucosinolates must therefore be converted to isothiocyanates and indoles in order to have anticancer effects. This occurs through the enzyme myrosinase, that is also present in brassica family vegetables. Normally, the myrosinase is present in a separate cellular compartment to the glucosinolates. Chewing and cooking brings the enzyme into contact with the glucosinolates and causes the formation of indoles and isothiocyanates.
Chewing Or Cooking?
Myrosinase is brought into contact with glucosinolates through the action of breaking cell walls. This can be accomplished by chewing or cooking. Chewing mechanically breaks the walls whereas cooking causes disintegration through the action of heat. However, cooking is problematic because although it frees the myrosinase to interact with the glucosinolates, myrosinase itself is sensitive to heat and therefore degrades.
Overcooking brassica vegetables therefore causes deterioration of the myrosinase activity and a reduction in the amount of glucosinolates that are converted to the cancer preventive isothiocyanates and indoles. Chewing is a better method to protect the myrosinase, but raw brassica vegetables are not pleasant. Therefore steaming, which is less damaging to the myrosinase, but which allows adequate cell wall disintegration produces the highest amount of anti-cancer activity.