A mountain of fresh vegetables outside a shopping mall in Manila from 2006. Researchers at the University of Warwick Medical School say that over cooking vegetables destroys anti-cancer properties contained in most members of the Brassica genus, which include broccoli, cabbage, cauliflower and Brussel sprouts.(AFP/File/Jay Directo)

PARIS (AFP) - You can steam it, stir fry it, micro wave it or eat it raw, but for heaven's sake don't do what the English do, don't boil that broccoli to death.

This "standard British cooking habit," say researchers at the University of Warwick Medical School, destroys precious anti-cancer properties contained in most members of the Brassica genus, which includes broccoli, cabbage, cauliflower and Brussel sprouts.

When consumed, a substance common to all these veggies called glucosinolate is metabolized into another compound -- isothiocyanate, pronounced eye-so-thigh-o-sigh-an-ate -- that counteracts the poisonous effect of cancer causing carcinogens and speeds up their removal from the body.

But boiling any of the "cabbage family" vegetables for 30 minutes leeches most of these medicinal properties away, according to a study published in the journal Food Chemistry and Toxicology.

Arguably, it also ruins the taste.

In experiments conducted by biochemists Paul Thornalley and Lijiang Song, the loss of glucosinolate content was 77 percent for broccoli, 58 percent for Brussel sprouts, 75 percent for cauliflower and 65 percent for green cabbage.

In contrast, the effects of steaming, micro-waving or stir-frying was negligible, they reported.

Other vegetables in the same group with anti-cancer properties include kale, turnips, collards, kohlrabi, rutabaga, Chinese cabbage, bok choy, horseradish, radish, and watercress.