A: A goitrogen is a substance that slows production of thyroid hormones, and chronically low levels of those hormones can rob you of energy and cause weight gain. When the gland tries to compensate by producing more hormones, it can enlarge, forming a goiter. A number of foods contain goitrogens: broccoli, soybeans, spinach, cauliflower, Brussels sprouts, peanuts, strawberries, and cabbage, to name a few. But don't toss out your produce. If your thyroid is healthy and you get adequate iodine in your diet—which most of us do courtesy of iodized salt—then goitrogens will have no noticeable effect.
That's not true if you have thyroid disease, however. An impaired thyroid will be more vulnerable to the subtle effects of goitrogens, and they could tip you into hypothyroidism (underactive thyroid). There is also an increasingly accepted view that subtle degrees of hypothyroidism may be quite common and contribute to everything from fatigue to depression.
Still, I don't think the solution is to avoid strawberries or broccoli. If you have symptoms (fatigue, weight gain, depression, hair loss) or a family history of thyroid disease, your doctor can administer a simple blood test to see if you require treatment. Should you need thyroid hormone pills to restore the gland's function, you may want to avoid goitrogens for a while. But once your hormone levels reach normal and are stable, you can go back to eating broccoli.