British researchers found that boiling cruciferous vegetables (broccoli, cabbage, Brussels sprouts, cauliflower) destroys the glucosinolates, contained in them. In the body glucosinolates are converted to isothiocyanates – fighting compounds.
Their study showed that stir-frying, microwaving for up to 3 min or steaming for up to 20 min didn’t show significant reduction in the amount of glucosinolates.
So, if you are concerned about containing the health important nutrients in your veggies, make sure you avoid boiling as a method of cooking.