A carbohydrate diet rich in sucrose increased insulin and WAT in macronutrient self-selecting rats.

In order to evaluate the influence of a carbohydrate (CHO) diet rich in sucrose (37%) on food choice and body composition, Wistar rats received a food selection diet (protein, CHO, fat) from the time of weaning to 13 weeks of age. Three groups of animals were examined: the first received a CHO diet containing 37% sucrose; the second, a diet containing only 10% sucrose; and the third, control group, received a complete standard diet (14% protein, 72% CHO including 10% sucrose). Food intakes and body weight (BW) were recorded four times a week. No differences in total food intake were observed between the two self-selecting groups and the control group, and no differences were observed between the two self-selecting groups in terms of their protein intake (about 45% of the total calorie intake). The latter groups modified their selections during the 10-week period, but the variations were similar. BW gain in the 37% group was lower but the white adipose tissue (WAT)/total BW ratio was significantly higher than those seen in the control and 10% groups. Insulinemia was higher in 37% and control groups. In conclusion, the high preferences for protein and fat were identical, whatever the CHO diet composition. The sucrose level in the diet was an essential factor for the development of hyperinsulinemia, leptin resistance and thus a higher prevalence of obesity. These results confirm the importance of the quality of CHO sources in the diet.

Daily delivery of dietary nitrogen to the periphery is stable in rats adapted to increased protein intake.

Dietary nitrogen was traced in rats adapted to a 50% protein diet and given a meal containing 1.50 g (15)N-labeled protein (HP-50 group). This group was compared with rats usually consuming a 14% protein diet and fed a meal containing either 0.42 g (AP-14 group) or 1.50 g (AP-50 group) of (15)N-labeled protein. In the HP group, the muscle nonprotein nitrogen pool was doubled when compared with the AP group. The main adaptation was the enhancement of dietary nitrogen transferred to urea (2.2 +/- 0.5 vs. 1.3 +/- 0.1 mmol N/100 g body wt in the HP-50 and AP-50 groups, respectively). All amino acids reaching the periphery except arginine and the branched-chain amino acids were depressed. Consequently, dietary nitrogen incorporation into muscle protein was paradoxically reduced in the HP-50 group, whereas more dietary nitrogen was accumulated in the free nitrogen pool. These results underline the important role played by splanchnic catabolism in adaptation to a high-protein diet, in contrast to muscle tissue. Digestive kinetics and splanchnic anabolism participate to a lesser extent in the regulation processes.

Repeated short-fasting modifies the macronutrient self-selection pattern in rats.

The daily caloric intake and circadian pattern of macronutrient self-selection were examined in rats subjected to 3 h of food and water deprivation at the beginning or at the end of darkness. When one sole 3-h period of deprivation was applied, rats showed a compensatory response characterized by an unscheduled diurnal and nocturnal increase in the intake of the three macronutrients. However, repeated short restrictions during 15 days promoted a scheduled time-dependent feeding response, characterized by an exclusive increase in carbohydrate and fat intake and a decrease in protein intake. Repeated deprivation at the onset of dark produced a feeding response confined to the dark phase, while late dark deprivation produced both a diurnal and nocturnal increase in feeding. After 15 days of repeated restriction, rats showed no body weight variations with respect to control rats fed ad libitum. These results show that short fasting elicits a time- and macronutrient-dependent feeding response in rats, which involves reorganization of the macronutrient self-selection pattern to promote a total daily caloric compensation. These results suggest that animals principally respond to the energy deficit produced by restriction.

Substrate oxidation during exercise in the rat cannot fully account for training-induced changes in macronutrients selection.

This study investigated spontaneous dietary adaptation to regular exercise in relation to substrate oxidation measured during exercise. Male Wistar rats were offered permanent access to the three sources of macronutrients supplemented with minerals and vitamins. The rats remained sedentary or were trained daily during 3 weeks at moderate intensity (20 m x min(-1), 2 hours). Body weight, total caloric intake, and macronutrients selection were recorded throughout the experiment. Energy expenditure and substrate oxidation were measured before, during, and after an exercise identical for trained and untrained rats (10 m x min(-1) 1 hour). Training reduced body weight gain (2.27 v 5.57 g x day(-1)), increased protein intake (52.6% v 39.2%), and decreased carbohydrate intake (21.3% v 39.5%). Basal and running energy expenditure, as well as glucose and lipid oxidation, remained essentially comparable in trained and untrained rats. The relative contribution of glucose oxidation (Gox) to total energy expenditure decreased during exercise (52.2%, average of all rats) relative to before exercise (60.8%). Gox during exercise was positively correlated with resting Gox before exercise, showing that preexercise substrate oxidation was a strong determinant of running substrate oxidation. However, the slope was smaller for the trained than for the untrained rats, showing that exercise increases Gox less in trained rats than in untrained ones. We conclude from this study that, since food selection but not substrate oxidation changed following training, food intake adapted to substrate requirements induced by regular training and not the contrary. However, large differences remained between the mixture ingested, in which lipids accounted for only 26% of the energy, and the mixture oxidized during exercise, in which lipids accounted for 50.7% of the substrate oxidized. Such a difference may be related to metabolic requirements during the rest of the day and/or to the distribution of macronutrients intake relative to exercise. This question deserves further investigation with recording of macronutrients selection, energy expenditure, and substrate oxidation over 24 hours.

Exercise training decreases body fat more in self-selecting than in chow-fed rats.

This study was designed to examine the influence of exercise training on body weight gain and feeding pattern in rats placed on a self-selection or a chow diet regimen. Adult, male, Wistar rats were submitted to daily 2-h treadmill exercise for 28 days (about 50% of VO2 max) at the beginning of the nocturnal period. Two other groups of rats were examined during the same time: a sedentary group that was deprived of food and water during the training session and a control group without any treatment. Food intakes were continuously recorded. For both feeding regimens, trained rats, relative to their respective controls, showed at the end of the experiment a reduction in body weight gain due to a reduced body fat deposit. Moreover, white adipose tissue (WAT) mass of self-selecting rats was smaller than in chow-fed rats. Exercise training decreased plasma glucose level in chow-fed rats and plasma insulin level in self-selecting rats. In self-selecting rats, food intake was slightly increased due to enhanced protein intake during the nocturnal period and fat intake increased both during the nighttime and daytime periods, whereas in chow-fed rats, food intake was decreased during the daytime period. These results show that, in rats placed on a self-selection regimen, exercise training increased fat consumption but reduced WAT. This could be a consequence of an increased lipolytic capacity of adipocytes in self-selecting trained rats. Thus, it appears from these results that the diet's carbohydrate-to-fat ratio can be an important parameter in shaping the interaction between exercise and body weight.

Refeeding after prolonged fasting in rats: nycthemeral variations in dietary self-selection.

The influence of metabolic status on food selection during refeeding after fasting was investigated in rats fasted for a long period of time and subsequently given the choice of eating fat, protein, and carbohydrate individually. Rats were fasted until either metabolic phase 2 (essentially using lipids) or metabolic phase 3 (when there was a rise in protein utilization). The very large first meal of the refeeding was identical in the two groups of animals and consisted mainly of fat and protein. The observed diurnal hyperphagia persisted for 2 days in phase 2, while in phase 3 the hyperphagia persisted throughout the 8 observation days. Both periods of hyperphagia consisted of an increase in fat and in protein intakes. The nocturnal intake was increased, but to a lesser extent, on days 4 and 5 in phase 2 and on days 4, 5, and 6 in phase 3. These results can be related to the metabolic events present during the diurnal part of the nycthemeral cycle.

Modifications in dietary self-selection specifically attributable to voluntary wheel running and exercise training in the rat.

To explore the effects of physical exercise on total caloric intake, body weight gain, and dietary self-selection in rats, female rats of the Dark Agouti strain were placed on macronutrient self-selection. They had free access to running wheels during the whole experimental period. After 16 days of voluntary exercise only, they were trained on a motor-driven treadmill (16 m/min) at the beginning of the dark period. Runtime was progressively increased and reached 3 h per day (plateau). When trained, the rats decreased spontaneous wheel running. Voluntary wheel running did not modify body weight gain. However, it increased both carbohydrate and total caloric intakes. Exercise training reduced body weight gain, but did not further modify total caloric intake. Moreover it increased protein and reduced fat intakes. Most of the training-induced modifications were not side effects of fasting during exercise training.

Refeeding in fasted rats: dietary self-selection according to metabolic status.

We investigated the influence of the metabolic status rats have reached during a fast on their selection of protein, fat and carbohydrate when allowed to refeed after fasting for different lengths of time. They were refed either while essentially relying on lipid fuels (group 1), or while in the further stage when there is a rise in protein breakdown (group 2). In contrast to previous studies in which rats could not select macronutrients, there was no transitory anorexia during refeeding. Macronutrient selection as well as food and energy intake on the first day of refeeding were the same for both groups, total food intake being significantly larger than prior to the fast. However, there was thereafter a distinct pattern of diet selection: while fat intake progressively decreased in group 1, it increased until the fifth day in rats of groups 2. These rats, moreover, exhibited a further rise in protein intake. The data are discussed in relation to the optimization of the restoration of body fuel reserves according to the metabolic status reached at the end of a long fast.

Exercise-training reduces BAT thermogenesis in rats.

In the energy balance equation, physical activity represents one component of energy expenditure. From various studies it appears that exercise-training does not affect clearly thermogenesis which depends on brown adipose tissue (BAT) activity. In the present work we examine how exercise-training can influence food intake and body weight regulation in relation to BAT thermogenesis. The proton conductance of the uncoupling protein of BAT was examined in male adult Wistar trained 2 h/day for 20 days and compared to that of sedentary (2 h of fasting instead of exercise) or control animals. All animals were provided with separate sources of the 3 macronutrients (protein, fat and carbohydrate) containing an identical percentage of vitamins, salt mixture and cellulose powder. At the end of training, rats were placed at 5 degrees C during 10 days, then during 4 days at 28 degrees C. This condition has been demonstrated to favour and amplify BAT responsiveness to moderate modifications of stimulation. The body weight of trained rats became significantly lower than that of the control and sedentary rats and this difference persisted all throughout the experiment. When placed at 5 degrees C, all rats increased their total ingestion: control rats enhanced fat intake, while sedentary and trained rats enhanced carbohydrate ingestion. When placed at 28 degrees C, all rats had identical total energy and that of the 3 items intakes. BAT proton conductance was about 40% lower in the trained compared with the sedentary plus the control rats. This indicated a lower BAT thermogenic activity in the trained animals. It could be concluded that exercise-training in rats induces negative energy balance; the reduced BAT activity could restrain weight loss and overeating.

Exercise training modifies nutrient self-selection in rats.

Few studies have examined the effects of exercise training on macronutrient self-selection in rats. It has been observed that trained rats decreased carbohydrate and increased fat and protein intakes. In the present experiment, total energy intake and macronutrient self-selection were examined in adult male rats placed on a self-selection regimen and submitted to 2 h of treadmill exercise daily for 20 days at the beginning of the nocturnal period. Two control groups of rats were examined during the same time: a sedentary group that was food and water deprived during the same 2 h while trained rats were exercising, and a control group that was examined only for body weight gain and 24-h food intake. Food intakes of sedentary and trained rats were continuously recorded. At the end of the experiment, body weight of trained rats was lower than that of sedentary and control rats. The 24-h cumulative intake of trained rats was significantly reduced; this reduction was due to a decrease in fat intake, whereas carbohydrate intake was increased. In sedentary rats, 24-h intake was not modified but fat intake was significantly increased from the beginning to the end of the experiment. During the first 6 h of the night, protein and fat intakes of trained rats were reduced, and carbohydrate ingestion remained the same. Daytime food intake represented only 8.7% of the 24-h intake. Exercise training significantly increased this intake. It is noteworthy that during the middle part of the day (3-9 h) trained rats significantly enhanced protein and carbohydrate ingestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy balance in an inbred strain of rats: comparison with the Wistar strain.

Food intake and body weight gain were examined in two groups of male rats (7 weeks): an inbred strain, Dark Agouti (DA, n = 12) and a noninbred strain, Wistar (n = 13). The animals were allowed to select their diet from separate sources of the three macronutrients protein, fat, and carbohydrate. After 10 days of adaptation to the diets, body weights and food intakes were measured for 3 weeks. During this period, meal patterns were recorded for at least 5 days in each rat. Then, rats were switched to a chow diet (UAR, A.O4) for 10 days. The total caloric intake of DA rats was 60% that of Wistar rats, while their body weight gain was 25% that of Wistar rats (1.3 g/day in DA vs. 5.3 g in Wistar). However, when energy intake was related to total body weight, there was no difference in energy ingestion. It was observed that DA rats ingested mainly proteins (45%) and fats (41%), while Wistar rats ingested an identical proportion of proteins and carbohydrates (40%). The percent of total white adipose tissue to total body weight was identical in both strains (6% on average). Brown adipose tissue thermogenic activity of DA rats was threefold higher than in Wistar rats. This could be one of the elements responsible for the lower body weight gain of this group of rats. Self-selected food intake of the inbred DA strain of rats, in contrast to what was expected, was greatly variable.

Effects of acute treadmill exercise and delayed access to food on food selection in rats.

Total energy intake and macronutrient self-selection were examined in rats following forced exercise (2 h treadmill, 15 m/min) or after a similar period of food deprivation without exercise. Acute exercise was realized at the end of the daytime. Return to the home cage for food access after exercise or after the same period of fasting was delayed for 0, 30, and 90 min. It has been shown that rats decreased body weight after all exercise situations. Food intake after deprivation was decreased in the first 3 h but was not modified over 24 h. The 24-h energy intake after exercise was identically reduced in the three situations. Carbohydrate and protein intakes were significantly reduced just after exercise. Protein decrease persisted all through the night and, to a lesser extent, during the following nycthemere. Fat decrease appeared later and was significant in the last part of the night. Increasing the delay to food access after exercise did not modify the total energy intake, but it significantly reduced carbohydrate intake. Those results show that exercise has a longer influence on food intake and, specifically, on macronutrient selection, than just food deprivation. Various hypotheses regarding central (cerebral neurotransmitters) and peripheral factors could be evoked in order to explain these modifications in the self-selected diet after an acute exercise.

Dietary self-selection vs. complete diet: body weight gain and meal pattern in rats.

Food intake and body weight gain of male adult Wistar rats were examined in two groups of animals. One group (n = 14) was allowed to select its diet from separate sources of protein (casein, 3.1 kcal/g), fat (lard and sunflower oil, 7.9 kcal/g) and carbohydrate (CHO, starch and sucrose, 3.3 kcal/g). Another group (n = 10) received a nutritionally complete diet (3.3 kcal/g). After 2 weeks of adaptation to the diets, body weights and meal patterns were recorded for at least 4 days. The total caloric intake was nearly identical for the two groups of rats. Rats given dietary choice gained less weight over 4 days than rats fed chow and showed reduced feed efficiency. During the 24-h period, self-selecting rats consumed 20.8% of calories as proteins, 21% as fats and 58.2% as CHO. Self-selecting rats ate significantly less calories during the day than did rats given chow. The chow diet consisting of 17.3% calories as protein, 7.6% as fat and 75.1% as CHO. When comparing the self-selecting group nutrient intakes to those of chow-fed group it was observed that 24-h protein calorie intakes were identical in both groups. Fat intake was significantly higher and CHO reduced as compared to chow-fed rats. During the day, CHO intake was higher in self-selecting rats, and fat intake was not significantly reduced. During the night, protein and fat intakes were significantly higher in self-selecting rats, while CHO intake was significantly decreased, particularly in the last periods of the night.(ABSTRACT TRUNCATED AT 250 WORDS)

Feeding behavior in rats on a complete diet containing Concanavalin A.

Canavalia ensiformis is a tropical legume which could be used in animal feeding. However, it contains a lectin, Concanavalin A (Con A) which is harmful to animals. When rats are presented with a diet containing Con A, rejection of the food appears very soon after the beginning of ingestion. In order to examine this rejection phenomenon 3 studies were carried out. The rejection was found not to be due to a neophobic response, nor could it be attributed to a conditioned taste aversion. The gastric intubation study suggested the hypothesis that it could be the binding of the lectin to the glycosylated molecules from the gut membrane which impaired absorption and hence food intake.

Blood pressure responses and drinking following central angiotensin II in adult rats guanethidine-sympathectomised at birth.

Rats pups were sympathectomised with daily, for 3 weeks, injections of guanethidine (0.01 ml/g body weight), starting the second day after birth. They were separated from their respective dams at 6 weeks, and when they had reached their adult weight (350 g), the males were used to study the role of the sympathetic nervous system in the blood pressure and drinking responses to central injections of angiotensin II (AII, 250 ng). Littermates injected with 0.15 NaCl served as controls. Mean blood pressure was similar in both experimental and control groups (118 +/- 6 versus 128 +/- 4 mmHg) though the sympathectomised rats had a less stable baseline blood pressure than the controls. AII injected into the third cerebral ventricle produced similar increases in blood pressure and drinking responses in both groups. From these results we conclude that other systems appeared to have compensated for the lack of the sympathetic nervous system in normal blood pressure regulation and in stimulated (AII) blood pressure increases.

Body weight gain after VMH lesions in adult female rats guanethidine-sympathectomized at birth.

The role of the sympathetic nervous system in body weight gain produced by lesions of the ventromedial nucleus of the hypothalamus (VMH) was studied in adult female rats that had been sympathectomized from birth for 3 weeks with daily injections of guanethidine (0.01 ml/g body weight) starting the second day after birth. Female littermates injected with 0.15 M NaCl served as controls. Body weight gain during the dynamic phase after the VMH lesion was the same in the sympathectomized and control groups of rats, whereas the treated rats gained weight at a slower rate than the controls in the static phase. The increase in food intake stimulated by the VMH lesion peaked sooner and remained elevated longer in the controls than in the experimental animals despite the similar increases in body weight gain. These results indicate that the sympathetic nervous system may play an important role in body weight gain during the static phase following a VMH lesion in adulthood.

Influence of glucose, medium- and long-chain triglyceride gastric loads and forced exercise on food intake and body weight in rats.

The purpose of this study was to examine the effect of oesophageal loads of glucose, medium (MCT)-and long-chain (LCT) triglycerides, plus treadmill exercise on food intake and body weight in rats. On test days, male rats were administered a gastric aqueous solution of glucose, MCT, LCT or water via an oesophageal tube. One hour later, the animals were forced to run on a treadmill for two hours at a speed of 20 m/min at 0% grade. At the beginning of the 12-hour dark cycle (at 7 p.m.) runners were returned to their cages. On control days, the same gastric loads were administered, but the animals remained in their cages. Food intake was continuously measured during both the dark and light periods. A reduction in body weight and total food intake was found after exercise. The food intake suppressing effect of exercise was seen in the first hours of the dark period. Following MCT and LCT oil stomach loads FI decrease was comparable but the latency of the effect varied. Stomach loads of MCT oil induced a reduction in FI within the 0-3 h of food availability whereas LCT oil suppressed intake during the 3-6-h dark period. This could be explained by their different metabolite fate.

Monosodium glutamate as a palatability enhancer in the European diet.

Can monosodium glutamate (MSG) augment palatability in foods of the occidental diet? Its effects on the palatability of two experimental foods were investigated in 36 healthy young men and women. MSG improved palatability ratings, with an optimum at 0.6%. Weekly tests of free intake showed that subjects fed the experimental foods with 0.6% MSG added ate progressively more and faster, indicating increasing palatability with repeated exposure. The effects of MSG on familiar foods were investigated in a group of 65 institutionalized elderly persons. Spontaneous intake was measured at lunch time on 12 test days. Target foods (soup and vegetable) were served either without or with 0.6% MSG added. MSG facilitated intake of some but not all target foods, and was associated with positive (increased calcium and magnesium intake) or adverse (increased fat intake) nutritional effects. It is concluded that MSG can act as a palatability enhancer in the context of the French diet. It can facilitate long-term intake in both young and elderly persons but it should be utilized cautiously so as to improve nutrition.

Feeding pattern of liver-transplanted rats.

It has been proposed that the liver is involved in the control of food intake (FI). Various studies utilizing hepatic vagotomy have cast doubt on the role of hepatic metabolic receptors. Feeding patterns of male adult Lewis rats were continuously recorded in one group of animals after orthotopic liver transplantation (T), without reestablishing arterial flow. Rats of a second group were dearterialized (D) and had their livers freed from the hepatic pedicle, while rats of a third group were laparotomized (L) and served as sham-operated controls. Meal pattern analyses and body weight (BW) changes were followed after surgery. When T rats began to recover BW, a fourth nonoperated control group (C) was added with BW paired to the T group. From days 15 to 25 the T rats gained significantly less BW than C rats and their 24-hour FI was reduced: daytime FI was augmented while nighttime FI was decreased. Meal number was unchanged. Daytime meal size was increased while nighttime meal size was diminished. Between days 50-60, the BW gain of the T group was nearly identical to that of D or L rats from days 15-25. Data from these two periods were compared. The 24-hour FI was identical, nighttime FI remained significantly lower in T rats. Because of variation in BW recovery of the T rats an additional comparison was made between the T rats after they recovered their BW following surgery, and the D and L rats (days 15-25). All feeding pattern parameters were identical in T, D and L rats. Liver transplantation was followed only by small long-lasting changes.(ABSTRACT TRUNCATED AT 250 WORDS)