Low-protein diet-induced hyperphagia and adiposity are modulated through interactions involving thermoregulation, motor activity, and protein quality in mice.

Low protein (LP)-containing diets can induce overeating in rodents and possibly in humans in an effort to meet protein requirement, but the effects on energy expenditure (EE) are unclear. The present study evaluated the changes induced by reducing dietary protein from 20% to 6%-using either soy protein or casein-on energy intake, body composition, and EE in mice housed at 22°C or at 30°C (thermal neutrality). LP feeding increased energy intake and adiposity, more in soy-fed than in casein-fed mice, but also increased EE, thus limiting fat accumulation. The increase in EE was due mainly to an increase in spontaneous motor activity related to EE and not to thermoregulation. However, the high cost of thermoregulation at 22°C and the subsequent heat exchanges between nonshivering thermogenesis, motor activity, and feeding induced large differences in adaptation between mice housed at 22°C and at 30°C.

Intermittent access to a sucrose solution impairs metabolism in obesity-prone but not obesity-resistant mice.

Consumption of sugar-sweetened beverages is associated with overweight and obesity. In this study, we hypothesized that obesity-prone (OP) mice fed a high-fat high-sucrose diet (HFHS) are more sensitive to consumption of sucrose-sweetened water (SSW) than obesity-resistant (OR) mice. After 3weeks of ad libitum access to the HFHS diet (7.5h/day), 180 male mice were classified as either OP (upper quartile of body weight gain, 5.2±0.1g, n=45) or OR (lower quartile, 3.2±0.1g, n=45). OP and OR mice were subsequently divided into 3 subgroups that had access to HFHS (7.5h/day) for 16weeks, supplemented with: i) water (OP/water and OR/water); ii) water and SSW (12.6% w/v), available for 2h/day randomly when access to HFHS was available and for 5 randomly-chosen days/week (OP/SSW and OR/SSW); or iii) water and SSW for 8weeks, then only water for 8weeks (OP/SSW-water and OR/SSW-water). OR/SSW mice decreased their food intake compared to OR/water mice, while OP/SSW mice exhibited an increase in food and total energy intake compared to OP/water mice. OP/SSW mice also gained more body weight and fat mass than OP/water mice, showed an increase in liver triglycerides and developed insulin resistance. These effects were fully reversed in OP/SSW-water mice. In the gut, OR/SSW mice, but not OP/SSW mice, had an increase GLP-1 and CCK response to a liquid meal compared to mice drinking only water. OP/SSW mice had a decreased expression of melanocortin receptor 4 in the hypothalamus and increased expression of delta opioid receptor in the nucleus accumbens compared to OP/water mice when fasted that could explain the hyperphagia in these mice. When access to the sucrose solution was removed for 8weeks, OP mice had increased dopaminergic and opioidergic response to a sucrose solution. Thus, intermittent access to a sucrose solution in mice fed a HFHS diet induces changes in the gut and brain signaling, leading to increased energy intake and adverse metabolic consequences only in mice prone to HFHS-induced obesity.

Dietary fibers reduce food intake by satiation without conditioned taste aversion in mice.

It is well known that intake of dietary fiber (DF) potently decreases food intake and feelings of hunger and/or promotes satiety ratings. However, the mechanisms explaining these effects are not well characterized. This work was performed to determine which of satiation and/or satiety mechanisms provoke the decrease of food intake induced by DF in mice. We tested in an intra-group protocol a low-viscosity (LV, fructo-oligosaccharide), a viscous (VP, guar gum) and a high-viscosity (HV, mixture of guar gum and fructo-oligosaccharide) preload. These were given to mice by intra-gastric gavage. It appeared that viscous preloads such as VP and HV reduced the daily energy intake by 14% and 21% respectively. The strong effect of HV was mainly due to a large decrease of meal size (by 57%) and meal duration (by 65%) with no effect on ingestion rate during the first 30 min after administration. Therefore, the DF-induced decrease of energy intake was due to a satiation mechanism. This is further supported by a 3-fold increased sensitization of neurons in the nucleus of the solitary tract as observed by c-Fos protein immunolabelling. No compensation of food intake was observed during the rest of the day, a phenomenon that may be explained by the fact that metabolic rate remained high despite the lower food intake. We have also shown that the DF-induced inhibition of food intake was not paired with a conditioned taste aversion. To conclude, this work demonstrates that DF inhibits food intake by increasing satiation during ~1h after administration.

Dietary fibers solubilized in water or an oil emulsion induce satiation through CCK-mediated vagal signaling in mice.

This study focused on the fate of the satiating potency of dietary fibers when solubilized in a fat-containing medium. Fourteen percent of either guar gum (GG) or fructo-oligosaccharide (FOS) or a mixture of the 2 (GG-FOS, 5% GG and 9% FOS) were solubilized in water or an oil emulsion (18-21% rapeseed oil in water, v:v) and administered by gavage to mice before their food intake was monitored. When compared with water (control), only GG-FOS solubilized in water or in the oil emulsion reduced daily energy intake by 21.1 and 14.1%, respectively. To further describe this effect, the meal pattern was characterized and showed that GG-FOS increased satiation without affecting satiety by diminishing the size and duration of meals for up to 9 h after administration independently of the solubilization medium. The peripheral blockade of gut peptide receptors showed that these effects were dependent on the peripheral signaling of cholecystokinin but not of glucagon-like peptide 1, suggesting that anorectic signals emerge from the upper intestine rather than from distal segments. Measurements of neuronal activation in the nucleus of solitary tract supported the hypothesis of vagal satiation signaling because a 3-fold increase in c-Fos protein expression was observed in that nucleus after the administration of GG-FOS, independently of the solubilization medium. Taken together, these data suggest that a mixture of GG and FOS can maintain its appetite suppressant effect in fatty media. Adding these dietary fibers to fat-containing foods might therefore be useful in managing food intake.

Brain responses to high-protein diets.

Proteins are suspected to have a greater satiating effect than the other 2 macronutrients. After protein consumption, peptide hormones released from the gastrointestinal tract (mainly anorexigenic gut peptides such as cholecystokinin, glucagon peptide 1, and peptide YY) communicate information about the energy status to the brain. These hormones and vagal afferents control food intake by acting on brain regions involved in energy homeostasis such as the brainstem and the hypothalamus. In fact, a high-protein diet leads to greater activation than a normal-protein diet in the nucleus tractus solitarius and in the arcuate nucleus. More specifically, neural mechanisms triggered particularly by leucine consumption involve 2 cellular energy sensors: the mammalian target of rapamycin and AMP-activated protein kinase. In addition, reward and motivation aspects of eating behavior, controlled mainly by neurons present in limbic regions, play an important role in the reduced hedonic response of a high-protein diet. This review examines how metabolic signals emanating from the gastrointestinal tract after protein ingestion target the brain to control feeding, energy expenditure, and hormones. Understanding the functional roles of brain areas involved in the satiating effect of proteins and their interactions will demonstrate how homeostasis and reward are integrated with the signals from peripheral organs after protein consumption.

The calm mouse: an animal model of stress reduction.

Chronic stress is associated with negative health outcomes and is linked with neuroendocrine changes, deleterious effects on innate and adaptive immunity, and central nervous system neuropathology. Although stress management is commonly advocated clinically, there is insufficient mechanistic understanding of how decreasing stress affects disease pathogenesis. Therefore, we have developed a "calm mouse model" with caging enhancements designed to reduce murine stress. Male BALB/c mice were divided into four groups: control (Cntl), standard caging; calm (Calm), large caging to reduce animal density, a cardboard nest box for shelter, paper nesting material to promote innate nesting behavior, and a polycarbonate tube to mimic tunneling; control exercise (Cntl Ex), standard caging with a running wheel, known to reduce stress; and calm exercise (Calm Ex), calm caging with a running wheel. Calm, Cntl Ex and Calm Ex animals exhibited significantly less corticosterone production than Cntl animals. We also observed changes in spleen mass, and in vitro splenocyte studies demonstrated that Calm Ex animals had innate and adaptive immune responses that were more sensitive to acute handling stress than those in Cntl. Calm animals gained greater body mass than Cntl, although they had similar food intake, and we also observed changes in body composition, using magnetic resonance imaging. Together, our results suggest that the Calm mouse model represents a promising approach to studying the biological effects of stress reduction in the context of health and in conjunction with existing disease models.

The postprandial use of dietary amino acids as an energy substrate is delayed after the deamination process in rats adapted for 2 weeks to a high protein diet.

The aim of this study was to determine the contribution of dietary amino acids (AA) to energy metabolism under high protein (HP) diets, using a double tracer method to follow simultaneously the metabolic fate of α-amino groups and carbon skeletons. Sixty-seven male Wistar rats were fed a normal (NP) or HP diet for 14 days. Fifteen of them were equipped with a permanent catheter. On day 15, after fasting overnight, they received a 4-g meal extrinsically labeled with a mixture of 20 U-[(15)N]-[(13)C] AA. Energy metabolism, dietary AA deamination and oxidation and their transfer to plasma glucose were measured kinetically for 4 h in the catheterized rats. The transfer of dietary AA to liver glycogen was determined at 4 h. The digestive kinetics of dietary AA, their transfer into liver AA and proteins and the liver glycogen content were measured in the 52 other rats that were killed sequentially hourly over a 4-h period. [(15)N] and [(13)C] kinetics in the splanchnic protein pools were perfectly similar. Deamination increased fivefold in HP rats compared to NP rats. In the latter, all deaminated AA were oxidized. In HP rats, the oxidation rate was slower than deamination, so that half of the deaminated AA was non-oxidized within 4 h. Non-oxidized carbon skeletons were poorly sequestrated in glycogen, although there was a significant postprandial production of hepatic glycogen. Our results strongly suggest that excess dietary AA-derived carbon skeletons above the ATP production capacity, are temporarily retained in intermediate metabolic pools until the oxidative capacities of the liver are no longer overwhelmed by an excess of substrates.

Three-dimensional macronutrient-associated Fos expression patterns in the mouse brainstem.

BACKGROUND: The caudal brainstem plays an important role in short-term satiation and in the control of meal termination. Meal-related stimuli sensed by the gastrointestinal (GI) tract are transmitted to the area postrema (AP) via the bloodstream, or to the nucleus tractus solitarii (NTS) via the vagus nerve. Little is known about the encoding of macronutrient-specific signals in the caudal brainstem. We hypothesized that sucrose and casein peptone activate spatially distinct sub-populations of NTS neurons and thus characterized the latter using statistical three-dimensional modeling. METHODOLOGY/PRINCIPAL FINDINGS: Using immunolabeling of the proto-oncogene Fos as a marker of neuronal activity, in combination with a statistical three-dimensional modeling approach, we have shown that NTS neurons activated by sucrose or peptone gavage occupy distinct, although partially overlapping, positions. Specifically, when compared to their homologues in peptone-treated mice, three-dimensional models calculated from neuronal density maps following sucrose gavage showed that Fos-positive neurons occupy a more lateral position at the rostral end of the NTS, and a more dorsal position at the caudal end. CONCLUSION/SIGNIFICANCE: To our knowledge, this is the first time that subpopulations of NTS neurons have be distinguished according to the spatial organization of their functional response. Such neuronal activity patterns may be of particular relevance to understanding the mechanisms that support the central encoding of signals related to the presence of macronutrients in the GI tract during digestion. Finally, this finding also illustrates the usefulness of statistical three-dimensional modeling to functional neuroanatomical studies.

A high-fat diet attenuates the central response to within-meal satiation signals and modifies the receptor expression of vagal afferents in mice.

During digestion, macronutrients are sensed within the small intestine. This sensory process is dependent upon the action of gut mediators, such as cholecystokinin (CCK) or serotonin (5-HT), on vagal afferents that, in turn, convey peripheral information to the brain to influence the control of food intake. Recent studies have suggested that dietary conditions alter vagal sensitivity to CCK and 5-HT. This phenomenon may be of importance to the onset of eating disorders. The aim of the present study was thus to investigate the effects of subjecting mice to 15 days of either an HF diet (30% fat, 54% carbohydrate) or an NF diet (10% fat, 74% carbohydrate) on 1) daily and short-term food intake, 2) vagal sensitivity to peripheral anorectic factors and macronutrient loads, and 3) vagal afferent neuron receptor expression. The results indicated that compared with an NF diet, and while increasing food intake and body weight gain, an HF diet altered the short-term response to CCK-8 and intragastric macronutrient loads, while decreasing vagal activation by CCK-8 and modifying the receptor expression of vagal neurons. These findings, therefore, suggest that dietary intervention effect on food intake could be linked to changes in vagal afferent receptor profiles.

Fos-positive neurons are increased in the nucleus of the solitary tract and decreased in the ventromedial hypothalamus and amygdala by a high-protein diet in rats.

Transition from a normal- (NP) to a high-protein (HP) diet induces a rapid depression in food intake and a progressive but incomplete return to the initial intake during the succeeding days. The aim of this study was to determine which CNS regions are involved in the HP diet-induced satiety in rats. Brains were collected from 3 groups of adult rats after habituation to an NP diet (21 d), during the transition phase to a HP diet (2 d), or after habituation to the HP diet (21 d). Fos expression was measured in several brain areas that are involved in the control of food intake (solitary tract nucleus, anterior piriform cortex, lateral hypothalamus, arcuate nucleus, posterior para ventricular nucleus, medio ventral hypothalamus, dorso medial hypothalamus, amygdala, and accumbens nucleus). Changes occurred in the majority of these regions during the transition period from the NP diet to the HP diet. After habituation to the HP diet, significant changes in Fos expression were restricted to an increase in the nucleus of the solitary tract and a decrease in the ventromedial hypothalamus and the cortex of the amygdala. Considering the functional characteristics of these areas, the present results suggest that the vagus nerve conveys the information relative to the quantity of protein ingested, that hypothalamic sites regulate food intake and may alter sympathetic nervous system activity, and that higher brain functions such as memory processing by the limbic system or food reward system are involved in the HP diet-induced satiety in rats.

Bound ferulic acid from bran is more bioavailable than the free compound in rat.

Ferulic acid (FA) is reported as a good antioxidant absorbed by human or rat but only few data deal with the influence of the food matrix on its bioavailability and with its potential protection against cardiovascular diseases and cancer. Wheat bran is used as a source of ferulic acid, the compound being mainly bound to arabinoxylans of the plant cell walls. Pharmacokinetic profiles of FA and its metabolites are established in rats. Free and conjugated FA quickly appear in plasma, reach a plateau 1 h after intake and remain approximately constant at 1 microM up to 24 h. 2.3% of FA are eliminated in urine. Compared with results obtained after intake of free FA, the presence of FA-arabinoxylans bonds in the food matrix increases the occurrence time of FA in the organism and decreases the level of urinary excretion in 24 h. Nevertheless, sulfated FA is still the main plasmatic form. The antioxidant activity of plasmas of rats fed with a standard diet (containing no FA), pure ferulic acid (5.15 mg FA/kg bw) or bran (4.04 mg FA/kg bw) are measured in an ex vivo test using AAPH as free radical inducer. Plasmas of rats fed with bran show a better antioxidant activity than the control group and the pure FA supplemented group, increasing the resistance of erythrocytes to hemolysis by factors of 2 and 1.5, respectively. These results show the good bioavailability of FA from bran and its potential efficiency to protect organism against pathology involving radical steps of development.

Total subdiaphragmatic vagotomy does not suppress high protein diet-induced food intake depression in rats.

This study was undertaken to determine whether the subdiaphragmatic vagus nerve is involved in the depression of food intake induced by the ingestion of a high protein diet (P50) in rats. After total subdiaphragmatic vagotomy (Vago group) or sham surgery (Sham group), rats consumed the control diet for a 2-wk recovery period and then both groups consumed the high protein diet for 16 d. Daily food intake, meal pattern analysis and behavioral satiety sequence were measured. Total subdiaphragmatic vagotomy did not modify the daily intake of the control diet or suppress the dramatic depression in food intake produced by acute transition to a high protein diet. However, the daily intake of a high protein diet was slightly reduced under acute conditions or even after adaptation (P < 0.005). Analysis of meal parameters and the behavioral satiety sequence after adaptation indicated no major metabolic distress. In conclusion, these results suggest that the subdiaphragmatic vagus nerve does not constitute an obligatory pathway for the transfer of information to the brain, resulting in a depression of high protein diet intake. In contrast, a defect in this visceral regulating system could reinforce the metabolic-associated food intake depression signal.

Body weight, body composition, and energy metabolism in lean and obese Zucker rats fed soybean oil or butter.

BACKGROUND: Dietary fat composition is thought to affect body weight regulation independent of the amount of fat ingested. OBJECTIVE: We analyzed the feeding behavior, body weight gain, body composition, and energy metabolism in lean and obese rats fed a diet in which fat was in the form of either butter or soybean oil. DESIGN: Ten lean (Fa/?) and 10 obese (fa/fa) adult Zucker rats were divided into 4 groups according to a 2 x 2 experimental design. They were fed a normally balanced diet over 11 wk in which 30% of energy was either soybean oil or butter. Food intake, body weight gain, and body composition were measured. Indirect calorimetry was used to study energy metabolism at rest and in relation to feeding and activity. RESULTS: Food intake increased similarly in lean and obese rats after butter feeding. Body weight gain increased in obese rats and decreased in lean rats after butter feeding. Body weight gain in obese rats was due mainly to an increase in the weight of lean tissues besides muscle, whereas adiposity and distribution of fat between the various pads did not change. Resting metabolic rates and postprandial lipid oxidation increased in butter-fed obese rats. Lipid oxidation during exercise was not significantly different between obese and lean rats. Fat oxidation increased in butter-fed lean rats during treadmill running at moderate intensity. CONCLUSIONS: In obese rats, basal metabolism and postprandial lipid oxidation increased during butter feeding, which appeared to prevent fat accumulation in the long term. In lean rats, butter feeding favored lipid utilization by working muscles, an observation that deserves further investigation in terms of endurance and performance.