A high-fat diet increases calcitonin secretion in the rat

We have studied the effects of diet-induced obesity on thyroidal calcitonin, plasma calcitonin, calcium and phosphorus in rats. Twelve 9-week-old female rats were randomly divided into two groups. One group was fed a low-fat diet while the other was fed a high-fat diet. Both diets had 0.76% Ca, 0.56% P and 2.2 U/g vitamin D; however, the high-fat diet had hydrogenated vegetable oil added at 405 g/kg. All rats were pair-fed and consumed 11 g/day per rat for 27 weeks at which time the rats were fasted overnight and exsanguinated. The rats on the high-fat diet weighted 406 +/- 21 g (mean +/- SEM) versus 292 +/- 13 g for controls and had higher levels of serum calcitonin (104 +/- 12 versus 57 +/- 9 pg/ml). The obese rats also had increased thyroidal calcitonin by radioimmunoassay and increased thyroidal C-cells by immunohistology. The increased calcitonin levels occurred without a concomitant increase in calcium levels. These data indicate that a high-fat diet in rats stimulates C-cell growth and calcitonin secretion.