(1) Some of the effects were examined of feeding Sprague-Dawley rats with diets rich in fat, starch or sucrose, and with adequate or inadequate amounts of protein. (2) The diets produced differences in growth rate, carcass composition and glucose tolerance, and in levels of hepatic fat, hepatic cholesterol and plasma cholesterol, that varied with the age and sex of the animals, the duration of the experiment and whether the diets were adequate in essential fatty acids (EFA). (3) Thus, disagreement between workers regarding the effects of sucrose in producing a diminished rate of growth, a raised level of plasma cholesterol, impairment of glucose tolerance, and an increase – or decrease – in body fat or liver fat, can be explained by the different experimental conditions used in the different investigations.