Energy/protein ratio in natural ingredient diets for weanling rats

Nutritional considerations in the production of rodents for aging studies

Dietary restriction in the maintenance of animals for aging research has been the subject of intense recent interest. This interest may be justified. Current formulas for laboratory animal diets were a natural progression from those for farm animals, but the objectives and conditions for maintaining laboratory and farm animals are often quite different. Indeed, the practice of ad lib feeding current laboratory animal formulations may actually have deleterious effects that can be reduced or eliminated by restricting food intake. This paper reviews many of the major considerations in the development and application of dietary restriction protocols, including formulation, nutritional management during long-term studies, and practical considerations.

Dietary hyperphagia in rats: role of fat, carbohydrate, and energy content

Dietary energy, fat and carbohydrate content were varied to determine the nutritional factors responsible for hyperphagia induced by feeding rats high-fat diets. In the first experiment, rats were fed isoenergetic high-fat or high-carbohydrate diets for 2 weeks. Weight gain and energy intake were lower in rats given the high-fat diet. When some of the rats were switched to a diet that was high in fat, carbohydrate and energy, gram food intake was initially unchanged, resulting in a substantial increase in energy intake and weight gain. Energy intake gradually declined over the 4 weeks following the switch to the high-energy diet. In the second experiment, rats were fed high-fat diets that were either high or low in carbohydrate content and either high or low in energy content (kcal/g). Rats fed a high-fat diet that was high in energy and carbohydrate ate the most energy and gained the most body weight and carcass fat. In the third experiment, rats were fed high-carbohydrate diets varying in fat and cellulose content. Energy intake and body weight gain varied directly as a function of caloric density regardless of the fat or cellulose content of the diets. It is concluded that hyperphagia induced by feeding high-fat diets is not due to the high dietary fat content alone. Rather, high levels of fat, carbohydrate, and energy interact to produce overeating and obesity in rats fed high-fat diets.