Physiology&Behavior, Vol. 27, pp. 115-123. Pergamon Press and Brain Research Publ., 1981. Printed in the U.S.A. Metabolic Consequences of Food Restriction in Rats' F. B. LIMA, N. S. HELL) C. TIMO-IARIA, R. SCIVOLETTO, M. S. DOLNIKOFF AND A. A. PUPO Institute of Biomedical Sciences, University of Sdo Paulo Department of Physiology and Pharmacology, 05508 $6o Paulo SP, Brazil Received 12 February 1981 LIMA, F. B., N. S. HELL, C. TIMO-IARIA, R. SCIVOLETTO, M. S. DOLNIKOFF AND A. A. PUPO. Metabolic consequences offi~od restriction in rats. PHYSIOL. BEHAV. 27(1) 115--123, 1981.--Some aspects of carbohydrate metabolism were studied in rats subjected to food restriction (single daily meal offered during two hours, either diurnal or nocturnal) for a week. Nocturnal preference for the nocturnal meal was patent in spite of food restriction, inasmuch as the rats fed from 8:00 to 10:00 p.m. ingested significantly more than those fed from 8:00 to 10:00 a.m. The amount of food ingested by rats of both groups was lower than that ingested by the animals with free access to food (as evaluated in 24 hours); nevertheless, both food-restricted groups did not lose weight for the duration of the experiments. The more prominent carbohydrate metabolic adaptations to food-restriction were: (1) high hepatic glycogen concentration during the intermeai periods; (2) hyperglycemia in the 12, 14 and 16 hour intermeal periods; (3) insulinemia was lower than in rats having free access to food all day long; (4) gastric emptying was delayed. Food restriction Carbohydrate metabolism Feeding behavior COHN et al. [l] and Cohn and Joseph [2] observed that rats allowed to eat only for a short period every day had a more efficient meal utilization. In rats living on such a meal- feeding schedule, metabolic changes occur that propitiate a normal increase in weight in spite of the restriction imposed on food intake [10]. When the meal-feeding schedule is pro- longed the curves of increase in weight may even surpass that prevailing for rats allowed to free-feed [8]. Concomi- tantly, lipogenesis increases in liver and fatty tissue [12], the rate of radioactivity labeled acetate and glucose incorpora- tion into lipids [19] is enhanced, hepatic glycogen depletion during fasting is lowered [11,19], and glycogen accumulates even more conspicuously after meals [18]. Glycogen reten- tion was also found to occur in muscle [11] and adipose tissue [13]. Food restriction during one week causes a greater resist- ance to glycogen depletion when rats are subjected to insulin administration; the reduction of depletion was less pro- nounced when the inter-meal periods were extended to eight hours, although glycogenolysis was always lesser than that found in non-fasting rats [7]. Such metabolic adaptations to food restriction seem to result from complex neuroendo- crine events, as suggested by the degree of hypoglycemia produced by insulin (0.025 U/100 g b.w.) being similar in both groups but recovery from hypoglycemia occurring only in the meal-fed animals 120 minutes after insulin injection. It is likely that the above metabolic changes play an important role in glucose homeostasis and in conditions which require a prompt mobilization of energetic substrate during a pro- longed fast. In accordance with this hypothesis, rats with free access to food exhibit a normal depletion of hepatic glycogen when food-deprived during 24 hours; however, after 48 to 120 hours near 25% of the glycogen concentration in liver (as related to the level of 24 hours fast) is restored, in association with enzymatic changes that favor its synthesis [5]. In the present experiment we studied some metabolic adaptations resulting from food restriction in rats trained to live on a single daily meal, either diurnal or nocturnal. METHOD In 639 male Wistar albino rats, weighing near 200 g, food consumption, glycemia, insulinemia, liver glycogen content and weight of the stomach with its contents were determined in three experimental groups: group D (allowed access only to a single meal during two hours every day, from 8:00 to 10:00 a.m.); group N (access to a single nocturnal meal, from 8:00 to 10:00 p.m.); and group AL (free access to food all day long). In order to keep the conditions otherwise as normal as possible, the experiments were carried out along twelve months under natural illumination and environmental tem- perature (which varied from 8°C in winter to 36°C in sum- mer). However, to assess the influence of such seasonal fac- tors on behavior and/or metabolism, experiments in the three series were repeated at different times of the year. The animals were kept in individual cages having free access to water and solid food (standard laboratory diet for rodents) for three or four days. Thereafter, each group was subjected to different feeding schedules for one week. The ~This research was supported by S~o Paulo State Foundation (FAPESP), National Research Council (CNPq) and FINEP. ~Reprints should be requested from this author. Copyright © 1981 Brain Research Publications Inc.--0031-9384/81/070115-09502.00/0