Thyroid and Pituitary Pathology in Iodine-deficient Rats Fed Fresh and Oxidized Fats and Oils

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Abstract
To study the long-term effects of feeding fresh and mildly oxidized cottonseed oil, olive oil, corn oil, soybean oil, chicken fat, beef fat, butter, and lard on thyroid pathology in iodine deficiency, these fats were fed, at a level of 20% in an iodine-deficient diet to male rats of the Columbia-Sherman strain. The incidence of thyroids weighing more than 100 mg was significantly higher in the rats fed vegetable oils even though the iodine intakes of all groups were approximately the same. This was interpreted as being due to the presence of goiterogenic substances in vegetable oils rather than to increased iodine requirements in the rats fed these oils. Pituitary tumors occurred in approximately 30% of the rats dying spontaneously after 600 days of age. Among the rats fed animal fats, the percentage of pituitary tumors among rats with thyroids weighing 100 mg or more was significantly higher than in rats with smaller thyroids. The percentage of tumors associated with heavy thyroids was significantly lower in the animals fed vegetable oils, although the overall tumor incidence was the same as in the rats fed animal fats. Therefore, whatever the cause of the increased incidence of large thyroids among the animals fed vegetable oils, the materials responsible did not affect the incidence of pituitary tumors.