Sulforaphane may help fight cancer by increasing detoxification enzyme activity, and cooking broccoli stimulates production of this powerful nutrient. However, research shows that heating broccoli to over 158 degrees Fahrenheit will decrease levels of sulforaphane, so steam broccoli lightly to about 140 degrees.

Eating a diverse diet that includes 5 servings of vegetables per day can make your real age as much as 4 years younger.

Avoid microwaving or boiling broccoli, which can deplete this vegetable of important nutrients. Lightly steaming it to 140 degrees Fahrenheit will produce the most cancer-fighting sulforaphane and also help preserve other nutrients, such as vitamin C, folate, and flavonoids. However, opposite cooking rules may apply to broccoli sprouts. Although high heat (158 degrees and above) decreases sulforaphane in broccoli, it stimulates sulforaphane production in broccoli sprouts. Maximizing your nutrients with the right cooking methods is only one small part of healthy living. To live younger longer and help reduce your cancer risk, don't smoke, eat a diverse diet with a variety of antioxidant-rich fruits and vegetables, get plenty of physical activity, and follow your healthcare provider's advice regarding regular medical screenings.

Ref:      Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoli. Matusheski, N. V., Juvik, J. A., Jeffery, E. H., Phytochemistry 2004 May;65(9):1273-1281.