Soybean Meal Reduces Tissue Iodine Concentration in Rats Administered Kombu

Abstract

Received: 12 January 2017 Revised: 24 March 2017 Accepted: 28 March 2017 Abstract Although high dietary iodine intake due to consumption of edible kelp (kombu) is observed, there are few health problems associated with iodine in Japan. Since several kinds of iso avones contained in soybeans act as goitrogens, the consumption of soybean may modify the adverse e ects of excess iodine derived from kombu. In the present study, to clarify the e ects of eating soybean meal on thyroid function and tissue distribution of iodine, we measured iodine content of serum and several organs in rats fed casein diet or soybean meal diet with or without kombu powder. Four types of experimental diet (casein diet, casein diet with 5% kombu, soybean meal diet, soybean meal diet with 5% kombu) were prepared using dried kombu powder (Saccharina diabolica; iodine content, 7.18 mg/ g). Twenty-four male 4-week-old Wistar rats were divided into four groups and fed these four diets for four weeks each. No signi cant di erences were observed in animal growth, thyroid weights, serum total thyroxine, triiodothyronine and thyroid stimulating hormone concentrations among the four groups. Irrespective of dietary protein (casein or soybean), the iodine content in thyroid gland of all four groups was signi cantly increased to a similar level by the administration of kombu. Iodine concentrations in serum, liver and kidney were also increased by the kombu, but the increases of iodine in these tissues were signi cantly lower in rats fed soybean than in those fed casein indicating that soybean meal reduced the content of iodine in serum, liver and kidney. ese results suggest that the consumption of soybean products could prevent the manifestation of adverse e ects due to an excess iodine intake from kombu.