[Effect of diet and thyroxine on body composition in rats]

In young male Wistar rats the influence of different fat content of the diet (7 or 25 or 50 weight percent of fat) and of thyroxine (5 or 50 microgram/100 g body mass, 2 times/week, sc.) on body composition was investigated by carcass analysis. After high doses of thyroxine the percentage body fat decreases and protein and water content increases within the same diet group (7 or 25 or 50% fat diet). Smaller doses of thyroxine have only the same effect as high thyroxine doses in the 7% fat diet group; the body composition is unchanged in the 25% fat diet group, and in rats after 50% fat diet thyroxine even brings about an increase in body fat. It is concluded that the fat content of the diet makes thyroxine partly ineffective. A comparison of the different diet groups, also with or without thyroxine treatment, brings the result of significantly increased percentage body fat after 25 and 50% fat diet; body protein and body water decreases respectively. It appears from the present study that controversial results in literature concerning body composition after thyroxine treatment, may be caused by different diets, especially the fat content of the diets.