I came across another section on foods in YOUR THYROID, A HOME REFERENCE, by Ridgway, Cooper and Wood, 1995 edition (p. 189).
“Much has been written about the effect of food upon the thyroid, yet most of what you eat does not present a danger to you. Kelp … may contain large amounts of iodine. Foods of the Brassica family (including cabbage, kale, rutabaga, and turnips) contain a substance that is capable of causing goiter in both animals and humans if their diet is deficient in iodine. Medical research suggests that these foods cause goiter and a decrease in thyroid funciton because they produce a chemical compound known as goitroin, which we know has a negative effect on the thyroid.
Another important foodstuff that may cause goiter in iodine-deficient individuals is the cassava which is a plant commonly eaten in tropical areas. An ingredient of cassava is converted by the body into thiocyanate, which can inhibit thyroid function.
These foods may produce goiter in people who live in iodine-deficient areas, but we are not aware of any case in which the thyroid has actually become underactive just because these foods were eaten in an area where there is sufficient dietary iodine.”