Behavioral, plasma, and calorimetric changes related to food texture modification in men

We hypothesized that food texture modifications might alter anticipatory reflexes, feeding behavior, and the postabsorptive consequences of ingestion. Two sets of complete meals with different textures but the same macronutrient composition were prepared. The first set was either a soup containing chunks of food (mixture) or the same soup blended until smooth (purée). The second set was either a rusk (R), a sandwich loaf (SL), or a liquid rusk meal (LR). We measured hunger and fullness feelings after ingestion of each food in a calibrated lunch, the ingestion rate, the duration between lunch and a spontaneous dinner request, the energy value, and the macronutrient composition of the ad libitum dinner. We also studied plasma modifications and respiratory gas exchanges from lunch to dinner. Feelings of hunger and fullness were not affected by texture modifications. The purée soup was consumed faster than the mixture (P < 0.05), and insulin, triacylglycerol, and energy expenditure were greater with the purée (P < 0.05). LR was less palatable than the other rusk lunch versions (P < 0.001), and R was ingested more slowly (P < 0.05). The lowest increase in plasma glucose occurred with SL, and the highest energy expenditure was seen with LR (P < 0.05). In humans, food texture modification affects not only eating patterns and palatability of ingestants but also metabolic management.     

Metabolic and hormonal response to short term fasting after endurance training in the rat

The metabolic and hormonal response to short term fasting was studied after endurance exercise training. Rats were kept running on a motor driven rodent treadmill 5 days/wk for periods up to 1 h/day for 6 wk. Trained and untrained rats were then fasted for 24 h and 48 h. Liver and muscle glycogen, blood glucose, lactate, beta OH butyrate, glycerol, plasma insulin, testosterone and corticosterone were measured in fed and fasted trained and untrained rats. 48 h fasted trained rats show a lower level of blood lactate (1.08 +/- 0.05 vs 1.33 +/- 0.08 mmol/l-1 of blood glycerol (1 +/- 0.11 vs 0.84 +/- 0.08 mmol/l-1), and of muscle glycogen. There is a significant increase in plasma corticosterone in 48 h fasted trained rats from fed values. Plasma testosterone decreases during fasting, the values are higher in trained rats. Plasma insulin decreases during fasting without any difference between the two groups. These results show higher lipolysis, and decreased glycogenolysis in trained animals during 48 h fasting. The difference between the groups in steroid hormone response could reduce neoglucogenesis and muscle proteolysis in trained animals.     

Peripheral ghrelin treatment stabilizes body weights of senescent male Brown Norway rats at baseline and after surgery

Unintentional weight loss may occur spontaneously in older humans and animals. Further weight losses after surgery or illness in the older patients result in increased morbidity, mortality, and hospital readmission rate. A growing body of work has shown increased appetite and weight gain in response to administration of ghrelin, the "hunger hormone." We conducted two studies in senescent male Brown Norway rats to assess the ability of peripheral administration of ghrelin to increase body weight and food intake. One study assessed the effect of 2 wk of daily subcutaneous ghrelin administration (1 mg.kg(-1).day(-1)) to senescent rats in a baseline condition; a second study used the same administration protocol in an interventional experiment with aged rats subjected to a surgery with 10-15% blood loss as a model of elective surgery. In both studies, animals receiving ghrelin maintained their body weights, whereas control animals lost weight. Body weight stability was achieved in ghrelin-treated animals despite a lack of increase in daily or cumulative food intake in both experiments. Hormone and proinflammatory cytokine levels were measured before surgery and after 14 days of treatment. Ghrelin treatment appeared to blunt declining ghrelin levels and also to blunt cytokine increases seen in the surgical control group. The ability of peripheral ghrelin treatment to maintain body weights of senescent rats without concomitant increases in food intake may be due to its known ability to decrease sympathetic activity and metabolic rate, perhaps by limiting cytokine-driven inflammation.     

Rapid Schedules for Koh Clearing and Alizarin Red S Staining of Fetal Rat Bone

Various schedules for staining fetal rat skeleton with alizarin red S were tested to determine a procedure that would produce a completely cleared and well-stained specimen in a short period of time. A 2 day procedure is presented which can produce specimens that are satisfactory but not completely transparent. A 7 day procedure produces cleared and stained specimens which can be well visualized with a dissecting microscope (30×). Fetal rats of 21 days gestation were fixed in 10% formalin for at least 1 wk. The specimens were skinned and eviscerated and then dehydrated in 2 changes of acetone for 12 hr (8 ml per gram body weight). The specimens were then placed in 1% KOM-alizarin red S (6 mg/liter) or 3 days, followed by 10% KOH-alizarin red S for 3 days. Finally, the specimens were placed in a mixture of benzyl alcohol, ethanol, and glycerol (1:2:2) (4 ml per gram body weight) for 12 hr, and then transferred to pure glycerol for storage.     

High-fat diet offsets the long-lasting effects of running-wheel access on food intake and body weight in OLETF rats

We have previously demonstrated that running-wheel access normalizes the food intake and body weight of Otsuka Long-Evens Tokushima Fatty (OLETF) rats. Following 6 wk of running-wheel access beginning at 8 wk of age, the body weight of OLETF rats remains reduced, demonstrating a lasting effect on their phenotype. In contrast, access to a high-fat diet exacerbates the hyperphagia and obesity of OLETF rats. To determine whether diet modulates the long-term effects of exercise, we examined the effects of high-fat diet on food intake and body weight in OLETF rats that had prior access to running wheels for 4 wk. We found that 4 wk of running exercise significantly decreased food intake and body weight of OLETF rats. Consistent with prior results, 4 wk of exercise also produced long-lasting effects on food intake and body weight in OLETF rats fed a regular chow. When running wheels were relocked, OLETF rats stabilized at lower levels of body weight than sedentary OLETF rats. However, access to a high-fat diet offset these effects. When OLETF rats were switched to a high-fat diet following wheel relocking, they significantly increased food intake and body weight, so that they reached levels similar to those of sedentary OLETF rats fed a high-fat diet. Gene expression determination of hypothalamic neuropeptides revealed changes that appeared to be appropriate responses to the effects of diet and running exercise. Together, these results demonstrate that high-fat diet modulates the long-lasting effects of exercise on food intake and body weight in OLETF rats.     

Pharmacological actions of the peptide hormone amylin in the long-term regulation of food intake, food preference, and body weight

The ability of amylin to reduce acute food intake in rodents is well established. Longer-term administration in rats (up to 24 days) shows a concomitant reduction in body weight, suggesting energy intake plays a significant role in mediating amylin-induced weight loss. The current set of experiments further explores the long-term effects of amylin (4-11 wk) on food preference, energy expenditure, and body weight and composition. Furthermore, we describe the acute effect of amylin on locomotor activity and kaolin consumption to test for possible nonhomeostatic mechanisms that could affect food intake. Four-week subcutaneous amylin infusion of high-fat fed rats (3-300 microg.kg(-1).day(-1)) dose dependently reduced food intake and body weight gain (ED(50) for body weight gain = 16.5 microg.kg(-1).day(-1)). The effect of amylin on body weight gain was durable for up to 11 wks and was associated with a specific loss of fat mass and increased metabolic rate. The body weight of rats withdrawn from amylin (100 microg.kg(-1).day(-1)) after 4 wks of infusion returned to control levels 2 wks after treatment cessation, but did not rebound above control levels. When self-selecting calories from a low- or high-fat diet during 11 wks of infusion, amylin-treated rats (300 microg.kg(-1).day(-1)) consistently chose a larger percentage of calories from the low-fat diet vs. controls. Amylin acutely had no effect on locomotor activity or kaolin consumption at doses that decreased food intake. These results demonstrate pharmacological actions of amylin in long-term body weight regulation in part through appetitive-related mechanisms and possibly via changes in food preference and energy expenditure.     

Effects on food intake and blood lipids of cannabinoid receptor 1 antagonist treatment in lean rats

Endocannabinoids act through the cannabinoid receptor 1 (CB1) and has both orexigenic and peripheral metabolic effects. It is not yet fully understood whether all the beneficial effects on the metabolic profile by CB1 antagonism are induced by the weight loss or also by direct peripheral effects. The present study was intended to further elucidate this question and to investigate whether tolerance development to the hypophagic effect could be attenuated by cyclic treatment. We performed an intervention study in 40 lean rats over 4 weeks. The rats were divided in four groups: a control group, two groups treated with the CB1 antagonist Rimonabant either continuously or cyclically, and one group pair fed with the continuous Rimonabant group to obtain the same body weight. During the first 6 days, food intake was less in the continuous Rimonabant group compared to the control group (P < 0.01). Throughout the study period, the cyclic Rimonabant group had a smaller food intake than the continuous Rimonabant group (P < 0.05). After 4 weeks, the cyclic Rimonabant group had a reduced weight gain compared to the control group (P < 0.05). Serum levels of glycerol and free fatty acids (nonesterified fatty acid, NEFA) were significantly reduced in both treated groups compared to the untreated groups, and levels of triglycerides showed the same tendency. Cyclic treatment with Rimonabant is able to inhibit tolerance development on food intake, which resulted in reduction in body weight. Rimonabant treatment is associated with reduced serum levels of glycerol, NEFA, and triglyceride which seem independent of body weight changes.     

Temperature-induced changes in metabolism and body weight of cattle (Bos taurus).

The metabolic and body weight changes in two non-pregnant beef cows were studied during prolonged exposure to warm (20 +/- 3 degrees C, relative humidity 50-70%) and cold (-10 +/- 2 or -25 +/- 4 degrees C) temperatures. Other factors including daily food intake were held constant throughout each 8-week exposure. During cold exposures, metabolic rate, blood hematocrit, and plasma concentrations of glucose and free fatty acid were elevated and respiratory frequencies and skin temperatures decreased. Resting metabolic rates measured at 20 degrees C, i.e., without the direct influence of cold, were 83.4-95.3 litres 02 per hour when the cows were cold acclimated, at either -10 or -25 degrees C, and 30-40% greater than when the cows were warm acclimated. The resting metabolic response and the concomitant reduction in intensity of shivering is indicative of metabolic acclimation to cold in these animals of greater than 500 kg body weight. As well as the expected changes in body weight with changes in energy metabolism there were losses in weight (13-24 kg) during the first 3 days of each cold exposure. Weight gains occurred when the cold stress was abruptly removed. These short term weight changes were associated with changes in water intake and apparent shifts in body fluid content.     

Modulatory role of food, feeding regime and physical exercise on body weight and insulin resistance

Energy intake and expenditure is a highly conserved and well-controlled system with a bias toward energy intake. In times of abundant food supply, individuals tend to overeat and in consequence to increase body weight, sometimes to the point of clinical obesity. Obesity is a disease that is not only characterized by enormous body weight but also by rising morbidity for diabetes type II and cardiovascular complications. To better understand the critical factors contributing to obesity we performed the present study in which the effects of energy expenditure and energy intake were examined with respect to body weight, localization of fat and insulin resistance in normal Wistar rats. It was found that a diet rich in fat and carbohydrates similar to "fast food" (cafeteria diet) has pronounced implication in the development of obesity, leading to significant body weight gain, fat deposition and also insulin resistance. Furthermore, an irregularly presented cafeteria diet (yoyo diet) has similar effects on body weight and fat deposition. However, these rats were not resistant to insulin, but showed an increased insulin secretion in response to glucose. When rats were fed with a specified high fat/carbohydrate diet (10% fat, 56.7% carbohydrate) ad lib or at the beginning of their activity phase they were able to detect the energy content of the food and compensate this by a lower intake. They, however, failed to compensate when food was given in the resting phase and gained more body weight as controls. Exercise, even of short duration, was able to keep rats on lower body weight and reduced fat deposition. Thus, inappropriate food intake with different levels of energy content is able to induce obesity in normal rats with additional metabolic changes that can be also observed in humans.     

Biometric evidence of diet-induced obesity in Lew/Crl rats

Although Lew/Crl rats are central to a classic model of renal transplantation and may provide a valid system for evaluating the effect of obesity on transplantation outcomes, their response to high-fat diet has not been evaluated sufficiently. The objective of this study was to evaluate biometric and basic metabolic data of Lew/Crl rats fed a 60% kcal, lard-based, very high-fat diet (HFD) compared with those fed a 10% kcal fat control diet (CD). Rats were maintained for 17 wk; body parameters and caloric intake were monitored weekly. Biometric data were collected and calculated before and after euthanasia. Serum was evaluated for liver enzyme activity and total bilirubin, glucose, triglyceride, cholesterol, insulin, leptin, and creatinine concentrations, and urine was evaluated for protein, glucose, specific gravity, and ketones. Tissues were harvested, weighed, and evaluated histologically. Compared with CD rats, HFD rats consumed more calories and weighed more after 3 wk. After 17 wk, HFD rats had significantly increased body weight, girth, volume, epididymal fat pad weight, omental weight, and body fat. In addition, HFD rats had mild elevations in some liver enzymes and a lower serum triglyceride concentration than did CD rats. Histologic assessment and other metabolic markers of disease were not different between the 2 groups. Lew/Crl rats fed a 60% kcal HFD become obese, but they lack significant metabolic abnormalities frequently associated with obesity in other rat strains.     

Changes in blood metabolic parameters during the development of Walker-256 tumour-induced cachexia in rats are not caused by decreased food intake

Blood metabolic parameters of Walker-256 tumour-bearing rats, on days 5, 8, 11 and 14 after implantation of tumour, were compared with those of rats without tumour fed ad libitum (free-fed control) or with reduced feeding (pair-fed control), similar to the anorexic tumour-bearing rats. Cachexia parameters and tumour mass also were investigated. In general, especially on day 14 after implantation of tumour, there was reduction of body mass, gastrocnemius muscle mass, food intake and glycemia and increase of blood triacylglycerol, free fatty acids, lactate and urea, compared with free-fed controls rats. These changes did not occur in pair-fed control, except a slight reduction of glycemia. Pair-fed control showed no significant changes in blood cholesterol and glycerol in comparison with free-fed control, although there was reduction of cholesterol and increase of blood glycerol on day 14 after tumour implantation compared with pair-fed control. The results demonstrate that, besides the characteristic signs of the cachexia syndrome such as anorexia, weight loss and muscle catabolism, Walker-256 tumour-bearing rats show several blood metabolic alterations, some of which begin as early as day 5 after implantation of tumour, and are accentuated during the development of cachexia. Evidence that the alterations of blood metabolic parameters of tumour-bearing rats were not found in pair-fed control indicate that they were not caused by decreased food intake. These changes were probably mediated by factors produced by tumour or host tissue in response to the presence of tumour.     

Food Viscosity Influences Caloric Intake Compensation and Body Weight in Rats

Objective: To determine the effects of food viscosity on the ability of rats to compensate for calories in a dietary supplement. Research Methods and Procedures: In a series of four experiments, rats consumed dietary supplements equated for caloric and nutritive content but differing in viscosity. Experiments 1 to 3 examined the ability of the rats to compensate for the calories consumed in low‐ compared with high‐viscosity premeals by reducing intake of a subsequent test meal. Caloric compensation was assessed with a wide range of premeal viscosity levels and with two different non‐nutritive thickening agents. Experiment 4 assessed the effects of consuming daily a low‐viscosity compared with an equicaloric high‐viscosity dietary supplement on longer term body weight gain. Results: Consuming a lower viscosity premeal was followed by significantly more caloric intake (i.e., less caloric compensation) compared with consuming premeals with higher viscosity levels. This effect was not specific to one thickening agent. Furthermore, rats given a low‐viscosity supplement daily gained significantly more weight over a 10‐week period compared with rats given a high‐viscosity supplement. Discussion: The results of these experiments suggest that food viscosity may be an important determinant of short‐term caloric intake and longer term body weight gain.     

Effects of dietary calcium on growth and oviposition of the African land snail Limicolaria flammea (Pulmonata: Achatinidae)

In an attempt to elucidate the role of calcium in the life of the edible Achatinid snail, Limicolaria flammea (Miller) I investigated short and long term effects of calcium added to the food. The short term experiments lasted for 18, 30 and 32 weeks respectively, while the long term experiment to determine life time utilization of calcium carbonate lasted for 15 months. In the short term experiments, hatchlings were divided into densities of one, ten and 50 snails. In the 10 snail group, there was a positive correlation between calcium provision, body weight (t test, p < 0.01; r = 0.96, p < 0.0001) and shell length (t test, p < 0.01; r = 0.96, p < 0.00001). There was also a positive correlation between increase in shell length and availability of calcium in the 1 snail group (t test, p< 0.01; r = 0.99, p < 0.00001). In the 50-snail group, the correlation was positive for shell length of the snails (t test, p < 0.05; r = 0.99, p < 0.0001) and body weight (t-test, p < 0.05; r = 99, p < 0.00001). Mortality was very high in the snails deprived of calcium and they did not produce eggs. In the long term experiment, there were three feeding peaks in L. flammea. In the first feeding peak, amount of food and calcium ingested by the snails increased in the first three months of life. The second feeding peak occurred at six months of age, while the last occurred at 10 months of age. The amount of calcium ingested during the second peak decreased gradually in the 4th and 5th month. The amount of calcium ingested was lowest during the 3rd feeding peak. The period of highest weight gained by the snails was between the 1st and 6th month and then dropped at between six and 12 months of age which corresponds to the period of egg production. There were also three peaks of egg production; the first was between six and eight months (535 eggs), the second at between 10 and 11 months (350 eggs) and the third at 13 to 14 months (310 eggs) respectively.     

Repeated light-dark shifts speed up body weight gain in male F344 rats

This study is aimed at verifying the causal relationship of chronic circadian desynchronization and changes in body weight control. Eight male albino F344 rats aged between 12-15 wk were subjected to twice weekly 12-h shifts of the daily light-dark (LD) cycle for 13 wk (3 mo). Continuous circadian phase shifts consisting of intermittent phase delay and advance and reduced circadian amplitudes were consistently displayed in all five experimental rats implanted intraperitoneally with heart rate, body temperature, and activity transponders. The experimental rat maintained a greater body weight during LD shifts and even after 10 days of recovery than that of the age-matched control rat, which was maintained on a regular LD cycle. Body weight gain was greater in the first 2 mo of LD shifts in the experimental rat than in the control rat. Relative to the baseline, food intake and activity percentages were increased and reduced, respectively, for the experimental rats. Features of these results, such as increased body weight gain and food intake, and reduced activity, suggest a causal relationship of chronic circadian desynchronization and changes in body weight control in male albino F344 rats.     

A preexercise alpha-lactalbumin-enriched whey protein meal preserves lipid oxidation and decreases adiposity in rats

The composition of the preexercise food intake is known to affect substrate utilization during exercise and thus can affect long-term changes in body weight and composition. These parameters were measured in male rats exercised 2 h daily over 5 wk, either in the fasting state or 1 h after they ingested a meal enriched with glucose (Glc), whole milk protein (WMP), or alpha-lactalbumin-enriched whey protein (CPalphaL). Compared with fasting, the Glc meal increased glucose oxidation and decreased lipid oxidation during and after exercise. In contrast, the WMP and CPalphaL meals preserved lipid oxidation and increased protein oxidation, the CPalphaL meal increasing protein oxidation more than the WMP meal. At the end of the study, body weight was larger in the WMP-, Glc-, and CPalphaL-fed rats than in the fasted ones. This resulted from an increased fat mass in the WMP and Glc rats and to an increased lean body mass, particularly muscles, in the CPalphaL rats. We conclude that the potential of the CPalphaL meal to preserve lipid oxidation and to rapidly deliver amino acids for use during exercise improved the efficiency of exercise training to decrease adiposity.     

Diet-induced insulin resistance precedes other aspects of the metabolic syndrome

This study wasdesigned to examine the effects of a high-fat refined-sugar (HFS) or alow-fat complex-carbohydrate (LFCC) diet on insulin-stimulated skeletalmuscle glucose transport, plasma insulin, blood pressure, plasmatriglycerides, plasma glycerol, body weight, and body fat in femaleFischer rats. Insulin-stimulated glucose transport was significantlyreduced in the HFS group at 2 wk, 2 mo, and 2 yr, whereas serum insulinwas significantly elevated at all time points. Blood pressure was notsignificantly elevated in the HFS group until 12 mo, and all HFSanimals were hypertensive by 18 mo. Glycerol, triglycerides, andabdominal fat cell size were not significantly different at 2 wk butwere significantly elevated in the HFS rats at 2 and 6 mo. Body weight was similar in both groups until 20 wk on the diet, when the HFS ratsstarted to gain more weight. These results demonstrate that insulinresistance and hyperinsulinemia occur before the other manifestationsof the metabolic syndrome and that diet, not obesity, is the underlyingcause.

     

Effect of a high or low ambient perinatal temperature on adult obesity in Osborne-Mendel and S5B/Pl rats

Perinatal environment is an important determinant of health status of adults. We tested the hypothesis that perinatal ambient temperature alters sympathetic activity and affects body composition in adult life and that this effect differs between S5B/Pl (S5B) and Osborne-Mendel (OM) strains of rat that were resistant (S5B) or susceptible (OM) to dietary obesity. From 1 wk before birth, rat litters were raised at either 18 or 30 degrees C until 2 mo of age while consuming a chow diet. Rats were then housed at normal housing temperature (22 degrees C) and provided either high-fat or low-fat diet. OM rats initially reared at 18 degrees C gained more weight on both diets than those reared at 30 degrees C. Perinatal temperature had no effect on body weight gain of the S5B rats on either diet. At 12 wk of age, OM and S5B rats reared at 18 degrees C had higher intakes of the high-fat diet than those reared at 30 degrees C but lower beta3-adrenergic receptor (beta3-AR) and uncoupling protein-1 (UCP1) mRNA levels in brown adipose tissue (BAT). The increase in metabolic rate in response to the beta3-agonist CL-316243, was greater in both OM and S5B rats reared at 18 degrees C than in those reared at 30 degrees C. Perinatal temperature differentially affects body weight in OM and S5B rats while having similar effects on food intake, response to a beta3-agonist, and BAT beta3-AR and UCP-1. The data suggest that OM rats are more susceptible to epigenetic programming than S5B rats.     

Measurement of ad libitum food intake, physical activity, and sedentary time in response to overfeeding

Given the wide availability of highly palatable foods, overeating is common. Energy intake and metabolic responses to overfeeding may provide insights into weight gain prevention. We hypothesized a down-regulation in subsequent food intake and sedentary time, and up-regulation in non-exercise activity and core temperature in response to overfeeding in order to maintain body weight constant. In a monitored inpatient clinical research unit using a cross over study design, we investigated ad libitum energy intake (EI, using automated vending machines), core body temperature, and physical activity (using accelerometry) following a short term (3-day) weight maintaining (WM) vs overfeeding (OF) diet in healthy volunteers (n?=?21, BMI, mean ± SD, 33.2±8.6 kg/m(2), 73.6% male). During the ad libitum periods following the WM vs. OF diets, there was no significant difference in mean 3-d EI (4061±1084 vs. 3926±1284 kcal/day, p?=?0.41), and there were also no differences either in core body temperature (37.0±0.2°C vs. 37.1±0.2°C, p?=?0.75) or sedentary time (70.9±12.9 vs. 72.0±7.4%, p?=?0.88). However, during OF (but not WM), sedentary time was positively associated with weight gain (r?=?0.49, p?=?0.05, adjusted for age, sex, and initial weight). In conclusion, short term overfeeding did not result in a decrease in subsequent ad libitum food intake or overall change in sedentary time although in secondary analysis sedentary time was associated with weight gain during OF. Beyond possible changes in sedentary time, there is minimal attempt to restore energy balance during or following short term overfeeding. Trial registration: ClinicalTrials.gov NCT00342732.     

Reduced central leptin sensitivity in rats with diet-induced obesity

On low-fat chow diet, rats prone to diet-induced obesity (DIO) have increased arcuate nucleus neuropeptide Y (NPY) expression but similar leptin levels compared with diet-resistant (DR) rats (19). Here, body weight and leptin levels rose in DIO rats, and they defended their higher body weight after only 1 wk on a 31% fat high-energy (HE) diet. However, DIO NPY expression did not fall to DR levels until 4 wk when plasma leptin was 168% of DR levels. When switched to chow, DIO rats lost carcass fat (18). By 10 wk, leptin levels fell to 148% and NPY expression again rose to 150% of DR levels. During 4 wk of food restriction, DIO leptin fell by approximately 50% while NPY increased by 30%. While both returned to control levels by 8 wk, DIO rats still regained all lost weight when fed ad libitum. Finally, the anorexic effect of intracerebroventricular leptin (10 microg) was inversely correlated with subsequent 3-wk weight gain on HE diet. Thus NPY expression and food intake are less sensitive to the leptin's suppressive effects in DIO rats. While this may predispose them to develop DIO, it does not fully explain their defense of a higher body weight on HE diet.     

Metabolic adjustments with the development, treatment, and recurrence of obesity in obesity-prone rats

Obesity is reaching epidemic proportions and predisposes afflicted individuals to several comorbidities. For these individuals, losing weight has proven to be an easier feat than maintaining a reduced weight. In obesity-prone rats, we examined if there is a metabolic propensity to regain weight after a period of significant weight loss. Twenty-four-hour energy expenditure (EE), sleeping metabolic rate (SMR), and nonprotein respiratory quotient (NPRQ) were obtained by indirect calorimetry with urinary nitrogen analysis and normalized to fat mass (FM) and fat-free mass (FFM) acquired by dual-energy X-ray absorptiometry. Obesity-prone rats were examined after free access to a high-fat diet for 16 wk to establish the obese state. They were again examined after 2 wk of calorie restriction, which reduced body weight (14%) and FM (32%). Rats were again examined after a further 8 wk of intake-regulated weight maintenance or ad libitum feeding that led to weight regain. Metabolic data were compared with preobese and age-matched controls. Weight loss suppressed EE and SMR beyond what was expected for the change in metabolic mass. This elevated metabolic efficiency persisted throughout weight maintenance but resolved after 8 wk of regain. Adjusted NPRQ values were elevated in weight-maintained and weight-regaining rats, suggesting a preference for carbohydrate utilization. These data support the concept that weight reduction in obesity is accompanied by metabolic adjustments beyond the drive to consume calories that predispose to weight regain, and some aspects of this adjustment persist with prolonged weight maintenance and during weight regain.