The use of cruciferous vegetablesóthose in the cabbage familyóbegan 7,000 years ago in China and spread throughout Europe during the Middle Ages. The oldest writings emphasize the medicinal utility of crucifers, but these vegetables have now gained culinary importance worldwide.
When raw crucifers are chewed, or when microwaved and steamed crucifers are digested by intestinal bacteria, they release substances called goitrogens that increase the need for iodine when consumed in small amounts and can damage the thyroid gland when consumed in large amounts.
These goitrogens also inhibit the transfer of iodine into mother's milk.
Steaming crucifers until they are fully cooked reduces the goitrogens to one-third the original value on average. Since release of the goitrogens from steamed crucifers depends on intestinal bacteria, however, the amount released varies from person to person.
Boiling crucifers for thirty minutes reliably destroys 90 percent of the goitrogens.
Fermentation does not neutralize the goitrogens in crucifers. When foods like sauerkraut are consumed as condiments, however, the small amount of goitrogens within them is not harmful if one's diet is adequate in iodine.
An increased dietary intake of iodine compensates for the consumption of moderate amounts of crucifers but cannot reverse the effects of large amounts of crucifers.
Paradoxically, the goitrogens found in crucifers may offer some protection against cancer. The jury is still out on whether or not this is true.
The use of sauerkraut as a condiment and several servings of steamed crucifers per week is probably beneficial. People who consume more than this amount, especially lactating mothers, should be sure to obtain extra iodine in their diet from seafood. People who make liberal use of crucifers on a daily basis should boil a portion of them to avoid excessive exposure to goitrogens.
The safety of concentrated sources of crucifer-related chemicals such as broccoli sprouts or supplements containing indole-3-carbinol (I3C) and 3-3'-diindolylmethane (DIM) is questionable. These supplements should be avoided until continuing research can further elucidate their risks and benefits.