Energetics of meal patterns in rats

Abstract

Meal patterns in rats were examined as functions of the caloric density and availability of the diet. Three diets were used, a standard laboratory diet (3.6 kcal/g), a calorically diluted diet (2.7 kcal/g), and a calorically concentrated diet (4.5 kcal/g). After obtaining ad lib measures of meal patterns on each diet availability of food was constrained by requiring the rats to complete fixed ratio requirements of barpresses to obtain access to a meal. On all 3 diets, meal frequency decreased, while meal size and duration increased as functions of the ratio requirement. Under ad lib conditions and low ratio requirements, in comparison to the standard diet, meal frequency was greater on the diluted diet and less on the concentrated diet. Meal size did not vary as a function of diet on low ratio schedules. At high ratio requirements, rats continued to maintain caloric intake on the diluted diet by increasing meal frequency. On the concentrated diet, however, rats maintained intake at high ratio values by decreasing meal size rather than meal frequency. The results indicate that the rat can adopt a variety of strategies to solve the problem of controlling energy intake constant across the daily feeding cycle.