Relation of Thyroid Activity to Increased Metabolism Induced by Fat Deficiency

Abstract

A study was made of the growth rate, oxygen consumption and thyroid activity of rats maintained on a fat-free diet for 13 weeks. Similar observations were made on rats maintained isocalorically on a diet containing 30% of its calories in the form of cottonseed oil. These were compared with data from rats fed the complete diet in an amount necessary to maintain the same growth rate as that of animals int he fat-deficient series. Data confirm previous observations that fat deficiency causes an increased basal oxygen consumption and an increased energy expenditure manifested by less weight gain per calorie. The fat-free diet did not cause an increase in thyroid activity as measured by thyroid weight and histology, 24-hour I¹³¹ uptake, 24-hour PBI¹³¹, and biological I¹³¹ decay. An increase in rate of removal of inorganic I¹³¹ by some route other than the thyroid was suggested by the altered T/S and conversion ratios observed in the rats on the fat-deficient diet. It is concluded that the recorded increase in oxygen consumption seen in the fat-deficient syndrome is not due to an altered thyroid function.