NEW DELHI: Do you like your vegetables boiled? In the process, you could be squashing all their health benefits.

In the first-ever study that quantifies how much of nutrients are lost by boiling vegetables, a team of scientists from the University of Warwick has found that boiling Brassica vegetables such as broccoli, Brussels sprouts, cauliflower and green cabbage strips them of their anti-cancer properties by about 75%.

Past studies have shown that consumption of Brassica vegetables decreases the risk of cancer. This is because of the high concentration in Brassicas of substances known as glucosinolates, which are metabolised to cancer-preventing substances known as isothiocyanates.

However, before this research, it was not known how the glucosinolates and isothiocyanates were influenced by storage and cooking of Brassica vegetables.

Speaking to TOI, lead researcher Paul J Thornalley from Warwick Medical School, UK, said, "The best way to consume these vegetables is by steaming them for about 20 minutes. This helps retain the nutrients. Studies have shown that these vegetables decrease chances of cancer in the colon, bladder and lung by 60%. However, with no previous studies done to access the best way to cook these vegetables, we believe steaming them will improve their anti-cancer properties to 80%."

For the study, Thornalley and his colleague, Dr Lijiang Song, bought Brassica vegetables from a local store and transported them to the laboratory within 30 minutes of purchasing.

The effect of cooking on the glucosinolate content of vegetables was then studied by investigating the effects of cooking by boiling, steaming, microwave cooking and stir-fry.