There is conflicting advice regarding the relative healthfulness or harmfulness of cruciferous vegetables. On one side, you are advised to eat cruciferous vegetables in abundance because the more you eat, the less likely you are to develop thyroid -- and other -- cancers. On the other side, you are advised to limit your intake of cruciferous vegetables because they can cause hypothyroidism and goiters.
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It is important to first understand what cruciferous vegetables are. The word cruciferous refers to the cross--like pattern made by the four--petal formation of the vegetables, which can be seen on a Brussels sprout, a head of cabbage and a broccoli bud. Other members of the cruciferous family include mustard greens, kale, radishes, turnips, cauliflower and kohlrabi.
Cruciferous vegetables all contain glucosinolates, which form a substance called goitrin -- a hormone that interferes with the synthesis of thyroid hormone -- when they are metabolized. When animals eat large amounts of cruciferous vegetables, they develop hypothyroidism, which has caused speculation that humans might be similarly affected.
Unlike animals, humans only develop hypothyroidism when there is also an iodine insufficiency. Some doctors still recommend that thyroid patients limit their intake of cruciferous vegetables, even though iodine supplementation in the United States has basically eradicated iodine deficiency in this country, .
Cruciferous vegetables are among the most protective against cancer, according to a review of 206 human studies and 22 animal studies published in the October 1996 issue of the “Journal of the American Dietetic Association.” Cruciferous vegetables make up only about 10 to 25 percent of the vegetable consumption in a typical North American diet -- about 25 to 30 grams per day compared to nearly 100 grams per day in the typical Chinese diet. All vegetables are beneficial for cancer prevention, with special emphasis on brightly colored vegetables, dark green vegetables, allium vegetables like onions and garlic, and cruciferous vegetables. Currently, Americans eat only about 2.6 cups of vegetables and fruit each day compared to the 5.5 cup recommendation in the 2010 Dietary Guidelines For Americans.