Effects of repeated isocaloric macronutrient loads on daily food intake of rats

The effects of repeated administration of different macronutrient loads on spontaneous food intake and body weight of male Sprague-Dawley rats were studied. For 6 wk, eight groups of five rats each received two daily intragastric loads, 3.5 h apart, consisting of isocaloric amounts of one of the following: albumin, sucrose, cornstarch, corn oil, a mixture of the preceding four loads, butter, medium-chain triglyceride, or a noncaloric load of water. Spontaneous intakes of rat chow were measured 3.5 and 24 h after the first daily load. All the macronutrient loads depressed subsequent 3.5-h intakes more than the water load (P < 0.01), and protein loads depressed 3.5-h intakes the most (P < 0.01). The macronutrient loads also depressed 24-h intakes more than water loads (P < 0.01) but did not differ among themselves. The mixture load depressed 3.5- and 24-h food intakes by an amount comparable with the average effects of its component loads. Neither body weight nor body fat as measured by the Lee index differed among the groups after 6 wk. The results indicate that fairly accurate long-term regulation of spontaneous energy intake occurs regardless of the type of macronutrient in the load.