Nutritional implications of high-iodine egg diet in rats: effects on lipid metabolism and thyroid function

The effects of a diet including high-iodine eggs, containing much higher amounts of iodine than ordinary eggs, were investigated on lipid metabolism and thyroid function in rats. To a non-purified diet was added at the 1% (w/w) level ordinary egg power (OE diet: 35 micrograms iodine/100 g diet) or high-iodine egg powder (IE diet: 392 micrograms iodine/100 g diet). At 7 months and 19 months, feeding of the IE diet resulted in a lowered serum triacylglycerol level, elevated tissue lipoprotein lipase activity and a lowered lipid peroxide level in the brain. Although the serum total iodine level was 5 times higher in animals given the IE diet than in those given the OE diet, serum levels of thyroid-related hormones (TSH, T3 and T4) were not affected by feeding of the IE diet. In animals exposed to cold and given antithyroid drug treatment, the IE diet seemed to improve age-related defects in thermogenic and thyroid hormone responses to cold, and also to confer resistance to the antithyroid drug. These results suggest that iodine ingestion through high-iodine eggs modulates both lipid metabolism and thyroid function in rats.