Role of dietary fat in calorie intake and weight gain

Genetic or pharmacological GHSR blockade has sexually dimorphic effects in rodents on a high-fat diet

The stomach-derived hormone ghrelin regulates essential physiological functions. The ghrelin receptor (GHSR) has ligand-independent actions; therefore, GHSR gene deletion may be a reasonable approach to investigate the role of this system in feeding behaviors and diet-induced obesity (DIO). Here, we investigate the effects of a long-term (12-month) high-fat (HFD) versus regular diet on obesity-related measures in global GHSR-KO and wild-type (WT) Wistar male and female rats. Our main findings are that the GHSR gene deletion protects against DIO and decreases food intake during HFD in male but not in female rats. GHSR gene deletion increases thermogenesis and brain glucose uptake in male rats and modifies the effects of HFD on brain glucose metabolism in a sex-specific manner, as assessed with small animal positron emission tomography. We use RNA-sequencing to show that GHSR-KO rats have upregulated expression of genes responsible for fat oxidation in brown adipose tissue. Central administration of a novel GHSR inverse agonist, PF-5190457, attenuates ghrelin-induced food intake, but only in male, not in female mice. HFD-induced binge-like eating is reduced by inverse agonism in both sexes. Our results support GHSR as a promising target for new pharmacotherapies for obesity.

Genetic or pharmacological GHSR blockade has sexually dimorphic effects in rodents on a high-fat diet

The stomach-derived hormone ghrelin regulates essential physiological functions. The ghrelin receptor (GHSR) has ligand-independent actions, therefore, GHSR gene deletion may be a reasonable approach to investigate the role of this system in feeding behaviors and diet-induced obesity (DIO). Here we investigated the effects of a long-term (12 month) high-fat (HFD) versus regular diet on obesity-related measures in global GHSR-KO and wild type (WT) Wistar male and female rats. Our main findings were that the GHSR gene deletion protects against DIO and decreases food intake during HFD in male but not in female rats. GHSR gene deletion increased thermogenesis and brain glucose uptake in male rats and modified the effects of HFD on brain glucose metabolism in a sex-specific manner, as assessed with small animal positron emission tomography. RNA-sequencing was also used to show that GHSR-KO rats had upregulated expression of genes responsible for fat oxidation in brown adipose tissue. Central administration of a novel GHSR inverse agonist, PF-5190457, attenuated ghrelin-induced food intake, but only in male, not in female mice. HFD-induced binge-like eating was reduced by inverse agonism in both sexes. Our results support GHSR as a promising target for new pharmacotherapies for obesity.

Fat Quality Impacts the Effect of a High-Fat Diet on the Fatty Acid Profile, Life History Traits and Gene Expression in Drosophila melanogaster

Feeding a high-fat diet (HFD) has been shown to alter phenotypic and metabolic parameters in Drosophila melanogaster. However, the impact of fat quantity and quality remains uncertain. We first used butterfat (BF) as an example to investigate the effects of increasing dietary fat content (3-12%) on male and female fruit flies. Although body weight and body composition were not altered by any BF concentration, health parameters, such as lifespan, fecundity and larval development, were negatively affected in a dose-dependent manner. When fruit flies were fed various 12% HFDs (BF, sunflower oil, olive oil, linseed oil, fish oil), their fatty acid profiles shifted according to the dietary fat qualities. Moreover, fat quality was found to determine the effect size of the response to an HFD for traits, such as lifespan, climbing activity, or fertility. Consistently, we also found a highly fat quality-specific transcriptional response to three exemplary HFD qualities with a small overlap of only 30 differentially expressed genes associated with the immune/stress response and fatty acid metabolism. In conclusion, our data indicate that not only the fat content but also the fat quality is a crucial factor in terms of life-history traits when applying an HFD in D. melanogaster.

The Direct and Structure Effect of Income on Nutrition Demand of Chinese Rural Residents

Although a significant body of literature has analyzed the effect of income-mediated policies on nutrition, research on how income affect nutrition consumption is scant. This paper contributes to the literature by decomposing the overall income effect on rural residents' calorie intake into the direct income effect and the structure effect by building a simple theoretical model and conducting related empirical research with an instrumental variable (IV) approach. Using nationally representative data from China, we find that the structure effect of income, represented by fat share growth induced by income, occupies a considerable proportion (38.03%) of overall income effect. Additionally, we provide evidence of an asymmetric distributional effect of income on calorie intake. In particular, the structure effect of income substantially accounts for a larger proportion in the higher quantiles of the calorie intake distribution. Our findings help better evaluate the effectiveness of the income-mediated policies from quantity and structure perspectives in a comprehensive framework.

Garcinia mangostana extract and curcumin ameliorate oxidative stress, dyslipidemia, and hyperglycemia in high fat diet-induced obese Wistar albino rats

The aim of this study was to explore the effects of Garcinia mangostana (mangosteen) and Curcuma longa independently and synergistically in modulating oxidative stress, dyslipidemia, and hyperglycemia commonly observed in high-fat diet-induced obesity in rodent models. Male albino Wistar rats were divided into eight experimental groups, fed on a normal diet or high-fat diet (HFD), then given mangosteen extract (400 mg /kg /day) and/or curcumin (80 mg/kg /day) for 6 weeks. Oxidative stress markers, glucose, and lipid fractions were measured in the sera. Mangosteen pericarp extract (MPE) induced a remarkable decrease in BMI (from 0.86 to 0.81 gm/cm2), while curcuma either alone or in combination was more effective, as treated rats recorded BMIs of 0.78 and 0.79 gm/cm2, respectively. Regarding the antioxidant effects, MPE induced a significant increase of GSH in obese rats (123.86 ± 15.53 μg/ml vs 288.72 ± 121.37 μg/ml). As anti-atherogenic agents MPE demonstrate significant effect recorded higher level of HDL-C in treated animals, but ineefective as anti-dyslipidemic agent. Curcumin was more effective in reducing LDL-C levels in obese rats. Both extracts effectively reduced blood glucose. The present study demonstrated that MPE and curcumin were independently and synergistically effective in treating obesity-induced atherogenesis.

Dietary Options for Rodents in the Study of Obesity

Obesity and its associated metabolic diseases are currently a priority research area. The increase in global prevalence at different ages is having an enormous economic and health impact. Genetic and environmental factors play a crucial role in the development of obesity, and diet is one of the main factors that contributes directly to the obesogenic phenotype. Scientific evidence has shown that increased fat intake is associated with the increase in body weight that triggers obesity. Rodent animal models have been extremely useful in the study of obesity since weight gain can easily be induced with a high-fat diet. Here, we review the dietary patterns and physiological mechanisms involved in the dynamics of energy balance. We report the main dietary options for the study of obesity and the variables to consider in the use of a high-fat diet, and assess the progression of obesity and diet-induced thermogenesis.

Intergenerational transmission of the effects of maternal exposure to childhood maltreatment on offspring obesity risk: A fetal programming perspective

Childhood obesity constitutes a major global public health challenge. A substantial body of evidence suggests that conditions and states experienced by the embryo/fetus in utero can result in structural and functional changes in cells, tissues, organ systems and homeostatic set points related to obesity. Furthermore, growing evidence suggests that maternal conditions and states experienced prior to conception, such as stress, obesity and metabolic dysfunction, may spill over into pregnancy and influence those key aspects of gestational biology that program offspring obesity risk. In this narrative review, we advance a novel hypothesis and life-span framework to propose that maternal exposure to childhood maltreatment may constitute an important and as-yet-underappreciated risk factor implicated in developmental programming of offspring obesity risk via the long-term psychological, biological and behavioral sequelae of childhood maltreatment exposure. In this context, our framework considers the key role of maternal-placental-fetal endocrine, immune and metabolic pathways and also other processes including epigenetics, oocyte mitochondrial biology, and the maternal and infant microbiomes. Finally, our paper discusses future research directions required to elucidate the nature and mechanisms of the intergenerational transmission of the effects of maternal childhood maltreatment on offspring obesity risk.

Potential Cardiometabolic Health Benefits of Full-Fat Dairy: The Evidence Base

Since their inception in 1980, the Dietary Guidelines for Americans have promoted low- or fat-free dairy foods. Removing fat from dairy does not reduce putatively beneficial nutrients per serving, including calcium, vitamin D, and potassium. Additionally, links between saturated fat and dietary cholesterol intakes with cardiovascular disease risk have helped to sustain the view that low-fat dairy foods should be recommended. Emerging evidence shows that the consumption of full-fat dairy foods has a neutral or inverse association with adverse cardiometabolic health outcomes, including atherosclerotic cardiovascular disease, type 2 diabetes, and associated risk factors. Thus, although low-fat dairy is a practical, practice-based recommendation, its superiority compared with full-fat dairy is not obviously supported by results from recent prospective cohort studies or intervention trials. To evaluate the emerging science on full-fat dairy, a group of nutrition experts convened to summarize and discuss the scientific evidence regarding the health effects of consuming full-fat dairy foods. Future studies should focus on full-fat dairy foods (milk, yogurt, and cheese) in the context of recommended dietary patterns and consider meal composition and metabolic phenotype in assessing the relation between full-fat dairy consumption and cardiometabolic health.

Cinnamon attenuates adiposity and affects the expression of metabolic genes in Diet-Induced obesity model of zebrafish

The prevalence of obesity is increasing at an alarming rate worldwide with about 30% of the world population classified as obese. Obese body structure results when energy intake exceeds energy expenditure in an individual. Increase in the consumption of high-energy eatables, in the context of portion and energy provided, has resulted in obese populations which is becoming the leading cause of metabolic disorders related to morbidity. The obesity-related comorbidity is an enormous liability on health services and will affect measures taken in tackling the increasing obesity rate. Prevention of an obese phenotype is the most suitable long-term strategy. Another approach towards the treatment of obesity is weight management through phytotherapeutics. In this study, we explored the anti-obesity effects of Cinnamon (Cinnamomum zeylanicum) in adult male zebrafish. Through BMI measurements, blood glucose level analyses, serum triglyceride analyses, Oil Red O staining as well as quantitative Real Time-PCR, the ability of cinnamon to reduce metabolic disorders associated with obesity is investigated for the first time in a zebrafish model. Our studies indicate that cinnamon ameliorates the genotypic and phonotypic characteristics associated with obesity through lowering of BMI, blood glucose, triglyceride levels, lipid levels in the liver and through gene modulation.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

This paper reviews our present knowledge on the contribution of ceramide (Cer), sphingomyelin (SM), dihydroceramide (DhCer) and sphingosine-1-phosphate (S1P) in obesity and related co-morbidities. Specifically, in this paper, we address the role of acyl chain composition in bodily fluids for monitoring obesity in males and females, in aging persons and in situations of environmental hypoxia adaptation. After a brief introduction on sphingolipid synthesis and compartmentalization, the node of detection methods has been critically revised as the node of the use of animal models. The latter do not recapitulate the human condition, making it difficult to compare levels of sphingolipids found in animal tissues and human bodily fluids, and thus, to find definitive conclusions. In human subjects, the search for putative biomarkers has to be performed on easily accessible material, such as serum. The serum “sphingolipidome” profile indicates that attention should be focused on specific acyl chains associated with obesity, per se, since total Cer and SM levels coupled with dyslipidemia and vitamin D deficiency can be confounding factors. Furthermore, exposure to hypoxia indicates a relationship between dyslipidemia, obesity, oxygen level and aerobic/anaerobic metabolism, thus, opening new research avenues in the role of sphingolipids.

Macronutrient intake and physical activity levels in individuals with and without metabolic syndrome: An observational study in an urban population

BACKGROUND

We aimed to compare dietary macronutrient intake and physical activity level (PAL) between community-based samples of Iranian adults with metabolic syndrome (MetS+) and without metabolic syndrome (MetS-).

METHODS

This cross-sectional study was conducted among 3800 men and women aged 35-65 years. The International Diabetes Federation (IDF) criteria were used to define MetS. A 24-hour recall was used to evaluate dietary intake. The James and Schofield human energy requirements equations were used to calculate PAL and questions were categorized into time spent on activities during work (including housework), during non-work time, and in bed.

RESULTS

The mean ± standard deviation (SD)age of the MetS+ and MetS- subjects was, respectively, 48.8 ± 7.8 years (521 men and 1178 women) and 47.6 ± 7.5 years (714 men and 1222 women) (P = 0.930). The mean energy intake was higher in the MetS+ men compared with MetS- men (1977.4 ± 26.6 vs. 1812.7 ± 21.7 Kcal; P < 0.001). Crude and energy-adjusted intake from total fat was lower in MetS+ women compared with MetS- women (both P < 0.010). PALs were lower in MetS+ compared with MetS- participants (P < 0.001). After adjusting for confounders, no significant association was observed between the intake of individual macronutrients and MetS. In contrast, PAL was inversely associated with the incidence of MetS [OR = 0.34 (95% CI: 0.17-0.57); P < 0.001].

CONCLUSION

In the current study, there was an inverse relationship between PAL and the risk of MetS, but no association between individual dietary macronutrients intake and the incidence of MetS.

In the Grand Scheme of Things: Identifying Reproducible Microbial Signatures in Dietary Intervention Studies

Nutrition research is plagued by the reproducibility crisis. Reconciling nutrition studies involving microbiome data presents a modern challenge for researchers. In this issue of Cell Host & Microbe, Bisanz et al., 2019 demonstrate a comprehensive methodology for meta-analysis of microbiome sequence data from high-fat-diet intervention studies.

Effects of RVD-hemopressin (α) on feeding and body weight after standard or cafeteria diet in rats

Palatability and variety of foods are major reasons for hedonic eating, and hence for obesity. Hemopressin, a hemoglobin α chain-derived peptide, plays antagonist/inverse agonist role on cannabinoid (CB)1 receptors, while RVD-hemopressin(α)[RVD-hp(α)], a N-terminally extended form of hemopressin, has been reported as an allosteric modulator of CB1 and CB2 receptors. We investigated the effects of 14 daily intraperitoneal injections of RVD-hp(α), in Sprague-Dawley rats fed a highly palatable cafeteria-style (CAF) diet (30% fat, 56% carbohydrate, 14% protein; 4.20 kcal/g) compared to standard laboratory chow (STD) food (3.5% fat, 63% carbohydrate, 14% protein, 19.5% other components without caloric value; 3.20 kcal). Food intake, body weight and locomotor activity were recorded throughout the study. Finally, rats were sacrificed and agouti-related peptide (AgRP), neuropeptide Y (NPY), pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) and fatty acid amide hydrolase (FAAH) gene expression in the hypothalamus was measured by real-time reverse transcription polymerase chain reaction. We found that CAF diet increased food intake as compared to STD diet. In both STD and CAF diet fed rats, RVD-hp(α) treatment inhibited food intake, increased locomotor activity but did not modify body weight. In vehicle injected animals, CAF as compared to STD diet increased AgRP gene expression. RVD-hp(α) treatment decreased POMC mRNA levels in both diet groups and lowered the elevated AgRP levels induced by CAF diet. RVD-hp(α) treatment plays an anorexigenic role paralleled by increased locomotor activity both in STD and CAF diet fed rats. The inhibition of feeding could be partially mediated by lowering of hypothalamic POMC and AgRP gene expression levels.

Fish Oil Suppresses Body Fat Accumulation in Zebrafish

Zebrafish is an often used model of vertebrate lipid metabolism. In this article, we examined the effects of diets rich in fish oil, a dietary fat that has been shown to have antiobesity effects in mammals, or lard on body fat accumulation in zebrafish. Adult female zebrafish were fed a high-fat diet containing 20% (w/w) fish oil or lard for 4 weeks. Fish in the fish oil diet group had less body fat accumulation compared with those in the lard diet group. In the intestine, expression of genes for the alpha (hadhaa) and beta (hadhb) subunits of the beta-oxidation enzyme hydroxyacyl-Coenzyme A dehydrogenase/3-ketoacyl-Coenzyme A thiolase/enoyl-Coenzyme A hydratase was significantly increased in the fish oil diet group compared with the lard diet group (p < 0.05). In the liver, expression of the gene for fatty acid synthase (fasn) was significantly decreased in the fish oil diet group compared with the lard diet group (p < 0.05). These results suggest that the mechanisms underlying the antiobesity effect of fish oil are similar in zebrafish and mammals.

Increased susceptibility of post-weaning rats on high-fat diet to metabolic syndrome

The present study aimed to examine the effects of the types of high-calorie diets (high-fat and high-fat-high-sucrose diets) and two different developmental stages (post-weaning and young adult) on the induction of metabolic syndrome. Male, post-weaning and adult (3- and 8-week old, respectively) Sprague Dawley rats were given control, high-fat (60% kcal), and high-fat-high-sucrose (60% kcal fat + 30% sucrose water) diets for eight weeks (n = 6 to 7 per group). Physical, biochemical, and transcriptional changes as well as liver histology were noted. Post-weaning rats had higher weight gain, abdominal fat mass, fasting glucose, high density lipoprotein cholesterol, faster hypertension onset, but lower circulating advanced glycation end products compared to adult rats. This is accompanied by upregulation of peroxisome proliferator-activated receptor (PPAR) α and γ in the liver and receptor for advanced glycation end products (RAGE) in the visceral adipose tissue. Post-weaning rats on high-fat diet manifested all phenotypes of metabolic syndrome and increased hepatic steatosis, which are linked to increased hepatic and adipocyte PPARγ expression. Adult rats on high-fat-high-sucrose diet merely became obese and hypertensive within the same treatment duration. Thus, it is more effective and less time-consuming to induce metabolic syndrome in male post-weaning rats with high-fat diet compared to young adult rats. As male rats were selectively included into the study, the results may not be generalisable to all post-weaning rats and further investigation on female rats is required.

Maternal Cortisol During Pregnancy and Infant Adiposity: A Prospective Investigation

CONTEXT

Glucocorticoids play a key role during intrauterine development in cellular growth and differentiation. Evidence suggests that exposure to inappropriate concentrations of glucocorticoids during sensitive developmental periods may produce alterations in physiological systems that impact obesity risk.

OBJECTIVE

To elucidate the magnitude and stage-of-gestation-specific association of maternal cortisol concentrations during pregnancy with infant adiposity.

DESIGN, PARTICIPANTS, AND SETTING

Sixty-seven mother-child dyads recruited in early pregnancy at university-based obstetric clinics in Southern California were followed with serial assessments from early gestation through birth until 6 months postnatal age. Maternal cumulative cortisol production was assessed over each of 4 consecutive days in early (≅13 weeks), mid (≅24 weeks), and late pregnancy (≅30 weeks) (5 saliva samples/d × 4 days × 3 trimesters = 60 saliva samples/subject). Infant body composition was serially assessed in newborns (at ∼25 days postnatal age) and at ∼6 months age with dual-energy X-ray absorptiometry imaging.

RESULTS

After adjusting for key prenatal, birth, and postnatal covariates, higher maternal cortisol during the early third trimester (conditioned on prior early and midgestation cortisol concentrations) was significantly associated with a greater change in infant percent body fat from 1 to 6 months of age [partial r (adjusted for covariates) = 0.379, P = 0.007], accounting for ∼14% of the variance in this measure of childhood obesity risk.

CONCLUSION

The present findings suggest a stage-of-gestation-specific effect of maternal cortisol on infant adiposity gain in early postnatal life and provide evidence in humans to support the role of glucocorticoids in fetal programming of childhood obesity risk.

Fructooligosaccharides suppress high-fat diet-induced fat accumulation in C57BL/6J mice

Two experiments were performed to examine the effects of fructooligosaccharides (FOS) on the development of obesity. In the first experiment, Wistar rats were orally administered a 2.5 g/kg body weight lipid emulsion containing FOS, and the subsequent elevation of plasma triglycerides was significantly suppressed compared with that in rats receiving lipid emulsion alone. In the second experiment, C57BL/6J male mice were fed a high-fat "western" diet with or without 2.5% FOS supplementation (n = 10/group) ad libitum for 12 weeks. Body weight and percent body fat were lower in mice fed FOS than in controls. Furthermore, the weight of the visceral adipose tissue, and the weight and triglyceride content of the liver were significantly lower in the high-fat + FOS group. Fecal excretion of lipids was markedly enhanced by FOS consumption. These results indicate that dietary FOS suppress high-fat diet-induced body fat accumulation, and inhibit intestinal absorption of dietary fat.

Roux-en-Y gastric bypass in rats progressively decreases the proportion of fat calories selected from a palatable cafeteria diet

Roux-en-Y gastric bypass surgery (RYGB) decreases caloric intake in both human patients and rodent models. In long-term intake tests, rats decrease their preference for fat and/or sugar after RYGB, and patients may have similar changes in food selection. Here we evaluated the impact of RYGB on intake during a "cafeteria"-style presentation of foods to assess if rats would lower the percentage of calories taken from fat and/or sugar after RYGB in a more complex dietary context. Male Sprague-Dawley rats that underwent either RYGB or sham surgery (Sham) were presurgically and postsurgically given 8-days free access to four semisolid foods representative of different fat and sugar levels along with standard chow and water. Compared with Sham rats, RYGB rats took proportionally fewer calories from fat and more calories from carbohydrates; the latter was not attributable to an increase in sugar intake. The proportion of calories taken from protein after RYGB also increased slightly. Importantly, these postsurgical macronutrient caloric intake changes in the RYGB rats were progressive, making it unlikely that the surgery had an immediate impact on the hedonic evaluation of the foods and strongly suggesting that learning is influencing the food choices. Indeed, despite these dietary shifts, RYGB, as well as Sham, rats continued to select the majority of their calories from the high-fat/high-sugar option. Apparently after RYGB, rats can progressively regulate their intake and selection of complex foods to achieve a seemingly healthier macronutrient dietary composition.

Body fat accumulation in zebrafish is induced by a diet rich in fat and reduced by supplementation with green tea extract

Fat-rich diets not only induce obesity in humans but also make animals obese. Therefore, animals that accumulate body fat in response to a high-fat diet (especially rodents) are commonly used in obesity research. The effect of dietary fat on body fat accumulation is not fully understood in zebrafish, an excellent model of vertebrate lipid metabolism. Here, we explored the effects of dietary fat and green tea extract, which has anti-obesity properties, on body fat accumulation in zebrafish. Adult zebrafish were allocated to four diet groups and over 6 weeks were fed a high-fat diet containing basal diet plus two types of fat or a low-fat diet containing basal diet plus carbohydrate or protein. Another group of adult zebrafish was fed a high-fat diet with or without 5% green tea extract supplementation. Zebrafish fed the high-fat diets had nearly twice the body fat (visceral, subcutaneous, and total fat) volume and body fat volume ratio (body fat volume/body weight) of those fed low-fat diets. There were no differences in body fat accumulation between the two high-fat groups, nor were there any differences between the two low-fat groups. Adding green tea extract to the high-fat diet significantly suppressed body weight, body fat volume, and body fat volume ratio compared with the same diet lacking green tea extract. 3-Hydroxyacyl-coenzyme A dehydrogenase and citrate synthase activity in the liver and skeletal muscle were significantly higher in fish fed the diet supplemented with green tea extract than in those fed the unsupplemented diet. Our results suggest that a diet rich in fat, instead of protein or carbohydrate, induced body fat accumulation in zebrafish with mechanisms that might be similar to those in mammals. Consequently, zebrafish might serve as a good animal model for research into obesity induced by high-fat diets.

Oestradiol and diet modulate energy homeostasis and hypothalamic neurogenesis in the adult female mouse

Leptin and oestradiol have overlapping functions in energy homeostasis and fertility, and receptors for these hormones are localised in the same hypothalamic regions. Although, historically, it was assumed that mammalian adult neurogenesis was confined to the olfactory bulbs and the hippocampus, recent research has found new neurones in the male rodent hypothalamus. Furthermore, some of these new neurones are leptin-sensitive and affected by diet. In the present study, we tested the hypothesis that diet and hormonal status modulate hypothalamic neurogenesis in the adult female mouse. Adult mice were ovariectomised and implanted with capsules containing oestradiol (E2 ) or oil. Within each group, mice were fed a high-fat diet (HFD) or maintained on standard chow (STND). All animals were administered i.c.v. 5-bromo-2'-deoxyuridine (BrdU) for 9 days and sacrificed 34 days later after an injection of leptin to induce phosphorylation of signal transducer of activation and transcription 3 (pSTAT3). Brain tissue was immunohistochemically labelled for BrdU (newly born cells), Hu (neuronal marker) and pSTAT3 (leptin sensitive). Although mice on a HFD became obese, oestradiol protected against obesity. There was a strong interaction between diet and hormone on new cells (BrdU+) in the arcuate, ventromedial hypothalamus and dorsomedial hypothalamus. HFD increased the number of new cells, whereas E2 inhibited this effect. Conversely, E2 increased the number of new cells in mice on a STND diet in all hypothalamic regions studied. Although the total number of new leptin-sensitive neurones (BrdU-Hu-pSTAT3) found in the hypothalamus was low, HFD increased these new cells in the arcuate, whereas E2 attenuated this induction. These results suggest that adult neurogenesis in the hypothalamic neurogenic niche is modulated by diet and hormonal status and is related to energy homeostasis in female mice.

Fat Preference: a novel model of eating behavior in rats

Obesity is a growing problem in the United States of America, with more than a third of the population classified as obese. One factor contributing to this multifactorial disorder is the consumption of a high fat diet, a behavior that has been shown to increase both caloric intake and body fat content. However, the elements regulating preference for high fat food over other foods remain understudied. To overcome this deficit, a model to quickly and easily test changes in the preference for dietary fat was developed. The Fat Preference model presents rats with a series of choices between foods with differing fat content. Like humans, rats have a natural bias toward consuming high fat food, making the rat model ideal for translational studies. Changes in preference can be ascribed to the effect of either genetic differences or pharmacological interventions. This model allows for the exploration of determinates of fat preference and screening pharmacotherapeutic agents that influence acquisition of obesity.

Elevated objectively measured but not self-reported energy intake predicts future weight gain in adolescents

BACKGROUND

Although obesity putatively occurs when individuals consume more calories than needed for metabolic needs, numerous risk factor studies have not observed significant positive relations between reported caloric intake and future weight gain, potentially because reported caloric intake is inaccurate.

OBJECTIVE

The present study tested the hypothesis that objectively measured habitual energy intake, estimated with doubly labeled water, would show a stronger positive relation to future weight gain than self-reported caloric intake based on a widely used food frequency measure.

DESIGN

Two hundred and fifty-three adolescents completed a doubly labeled water (DLW) assessment of energy intake (EI), a food frequency measure, and a resting metabolic rate (RMR) assessment at baseline, and had their body mass index (BMI) measured at baseline and at 1- and 2-year follow-ups.

RESULTS

Controlling for baseline RMR, elevated objectively measured EI, but not self-reported habitual caloric intake, predicted increases in BMI over a 2-year follow-up. On average, participants under-reported caloric intake by 35%.

CONCLUSIONS

RESULTS provide support for the thesis that self-reported caloric intake has not predicted future weight gain because it is less accurate than objectively measured habitual caloric intake, suggesting that food frequency measures can lead to misleading findings. However, even objectively measured caloric intake showed only a moderate relation to future weight gain, implying that habitual caloric intake fluctuates over time and that it may be necessary to conduct serial assessments of habitual intake to better reflect the time-varying effects of caloric intake on weight gain.

JTT-130, a novel intestine-specific inhibitor of microsomal triglyceride transfer protein, reduces food preference for fat

Microsomal triglyceride transfer protein (MTP) is involved in the assembly and secretion of triglyceride-rich lipoproteins from enterocytes and hepatocytes. JTT-130 is a novel intestine-specific MTP inhibitor, which has been shown to be useful in the prevention and treatment of dyslipidemia, obesity, and diabetes. JTT-130 has also been shown to suppress food intake in a dietary fat-dependent manner in rats. However, whether JTT-130 enables changes in food preference and nutrient consumption remains to be determined. Therefore, the aim of the present study was to investigate the effects of JTT-130 on food preference in rat under free access to two different diets containing 3.3% fat (low-fat diet, LF diet) and 35% fat (high-fat diet, HF diet). JTT-130 decreased HF diet intake and increased LF diet intake, resulting in a change in ratio of caloric intake from LF and HF diets to total caloric intake. In addition, macronutrient analysis revealed that JTT-130 did not affect carbohydrate consumption but significantly decreased fat consumption (P < 0.01). These findings suggest that JTT-130 not only inhibits fat absorption, but also suppresses food intake and specifically reduces food preference for fat. Therefore, JTT-130 is expected to provide a new option for the prevention and treatment of obesity and obesity-related metabolic disorders.

Relative ability of fat and sugar tastes to activate reward, gustatory, and somatosensory regions

BACKGROUND

Although the intake of high-fat and high-sugar food activates mesolimbic reward, gustatory, and oral somatosensory brain regions, contributing to overeating, few studies have examined the relative role of fat and sugar in the activation of these brain regions, which would inform policy, prevention, and treatment interventions designed to reduce obesity.

OBJECTIVE

We evaluated the effect of a high-fat or high-sugar equicaloric chocolate milkshake and increasing fat or sugar milkshake content on the activation of these regions.

DESIGN

Functional magnetic resonance imaging was used to assess the neural response to the intake of high-fat/high-sugar, high-fat/low-sugar, low-fat/high-sugar, and low-fat/low-sugar chocolate milkshakes and a tasteless solution in 106 lean adolescents (mean ± SD age = 15.00 ± 0.88 y). Analyses contrasted the activation to the various milkshakes.

RESULTS

High-fat compared with high-sugar equicaloric milkshakes caused greater activation in the bilateral caudate, postcentral gyrus, hippocampus, and inferior frontal gyrus. High-sugar compared with high-fat equicaloric milkshakes caused greater activation in the bilateral insula extending into the putamen, the Rolandic operculum, and thalamus, which produced large activation regions. Increasing sugar in low-fat milkshakes caused greater activation in the bilateral insula and Rolandic operculum; increasing fat content did not elicit greater activation in any region.

CONCLUSIONS

Fat caused greater activation of the caudate and oral somatosensory regions than did sugar, sugar caused greater activation in the putamen and gustatory regions than did fat, increasing sugar caused greater activity in gustatory regions, and increasing fat did not affect the activation. Results imply that sugar more effectively recruits reward and gustatory regions, suggesting that policy, prevention, and treatment interventions should prioritize reductions in sugar intake. This trial was registered at clinicaltrials.gov as DK092468.

Neuromedin U receptor 2 knockdown in the paraventricular nucleus modifies behavioral responses to obesogenic high-fat food and leads to increased body weight

Neuromedin U (NMU) is a highly conserved neuropeptide which regulates food intake and body weight. Transgenic mice lacking NMU are hyperphagic and obese, making NMU a novel target for understanding and treating obesity. Neuromedin U receptor 2 (NMUR2) is a high-affinity receptor for NMU found in discrete regions of the central nervous system, in particular the paraventricular nucleus of the hypothalamus (PVN), where it may be responsible for mediating the anorectic effects of NMU. We hypothesized that selective knock down of NMUR2 in the PVN of rats would increase their sensitivity to the reinforcing properties of food resulting in increased intake and preference for high-fat obesogenic food. To this end, we used viral-mediated RNAi to selectively knock down NMUR2 gene expression in the PVN. In rats fed a standard chow, NMUR2 knockdown produced no significant effect on food intake or body weight. However, when the same rats were fed a high-fat diet (45% fat), they consumed significantly more food, gained more body weight, and had increased feed efficiency relative to controls. Furthermore, NMUR2 knockdown rats demonstrated significantly greater binge-type food consumption of the high-fat diet and showed a greater preference for higher-fat food. These results demonstrate that NMUR2 signaling in the PVN regulates consumption and preference for high-fat foods without disrupting feeding behavior associated with non-obesogenic standard chow.

Composition of dietary fat source shapes gut microbiota architecture and alters host inflammatory mediators in mouse adipose tissue

BACKGROUND

Growing evidence shows that dietary factors can dramatically alter the gut microbiome in ways that contribute to metabolic disturbance and progression of obesity. In this regard, mesenteric adipose tissue has been implicated in mediating these processes through the elaboration of proinflammatory adipokines. In this study, we examined the relationship of these events by determining the effects of dietary fat content and source on gut microbiota, as well as the effects on adipokine profiles of mesenteric and peripheral adipocytes.

METHODS

Adult male C57Bl/6 mice were fed milk fat-based, lard-based (saturated fatty acid sources), or safflower oil (polyunsaturated fatty acid)-based high-fat diets for 4 weeks. Body mass and food consumption were measured. Stool 16S ribosomal RNA (rRNA) was isolated and analyzed via terminal restriction fragment length polymorphism as well as variable V3-4 sequence tags via next-generation sequencing. Mesenteric and gonadal adipose samples were analyzed for both lipogenic and inflammatory mediators via quantitative real-time polymerase chain reaction.

RESULTS

High-fat feedings caused more weight gain with concomitant increases in caloric consumption relative to low-fat diets. In addition, each of the high-fat diets induced dramatic and specific 16S rRNA phylogenic profiles that were associated with different inflammatory and lipogenic mediator profiles of mesenteric and gonadal fat depots.

CONCLUSIONS

Our findings support the notion that dietary fat composition can both reshape the gut microbiota and alter host adipose tissue inflammatory/lipogenic profiles. They also demonstrate the interdependency of dietary fat source, commensal gut microbiota, and inflammatory profile of mesenteric fat that can collectively affect the host metabolic state.

Influence of High Fat Diet Feeding for 20 Weeks on Lower Urinary Tract Function in Mice

OBJECTIVES

We investigated the possible changes in lower urinary tract function in mice fed a high fat diet (HFD).

METHODS

Male C57BL/6J mice were divided into two different feed groups: normal diet (ND) and HFD (n = 16 in each). The body weight, blood glucose level and voiding frequency/volume (FV) relations (for 24 h) were measured every 4 weeks. At 25 weeks old, blood pressure and heart rate, cystometry and isolated detrusor smooth muscle function were measured. After the experiments, serum fat level was measured.

RESULTS

The body weight and blood glucose level of the HFD group were significantly higher than those of the ND group after 9 weeks old. In the FV measurements, the mean voided volume was not significantly different between the two groups, although voiding frequency, total voided volume and water intake volume in the HFD group were significantly lower than those in the ND group. At 25 weeks old, the mean heart rate in the HFD group was significantly higher than that in the ND group, but no significant difference in the blood pressure was observed. None of the cystometric parameters analyzed showed significant differences between the two groups. The contractile response to either carbachol or high K(+) was not significantly different, whereas the contractile response to electrical field stimulation was significantly higher in the HFD group. In the HFD group, the mean total cholesterol level was significantly higher.

CONCLUSION

The present results suggest that HFD-feeding for 20 weeks in mice unlikely affects bladder function even though it induced diabetes, hyperlipidemia and tachycardia.

Ingestion of Carbohydrate-Rich Supplements during Gestation Programs Insulin and Leptin Resistance but not Body Weight Gain in Adult Rat Offspring

Prenatal nutritional conditions can predispose to development of obesity and metabolic syndrome in adulthood. Gestation with its important modifications in hormonal status is a period of changes in normal feeding habits with pulses of consumption or avoidance of certain categories of food. We tried to mimic in an animal model some changes in food consumption patterns observed in pregnant women. For this purpose, Long–Evans female rats were fed during the dark period, their usual pre-gestational food quantity, and were allowed to complete their daily intake with either a restricted control (Cr), high-fat (HF), or high-carbohydrate (HC) diet available ad libitum during the light period. Dams fed a control diet ad libitum (Ca) served as controls. Body weight and composition, food intake, and metabolic hormones (insulin, leptin) were recorded in male offspring until 20 weeks after birth. Cr and HC females ate less than Ca females (−16%; p < 0.001) and their offspring presented a weight deficit from birth until 6 (HC group) and 10 (Cr group) weeks of age (p < 0.05 or less). Plasma leptin corresponded to low body weight in Cr offspring, but was increased in HC offspring that in addition, had increased plasma insulin, blood glucose, and subcutaneous adipose tissue mass. HF dams ate more than Ca dams (+13%; p < 0.001), but plasma leptin and insulin were similar in their offspring. Hypothalamic Ob-Rb expression was increased in Cr, HC, and HF offspring (+33–100% vs Ca; p < 0.05 or less). HC supplement ingestion during gestation therefore leads to insulin and leptin resistance in adult offspring independently of lower birth weight. These hormonal changes characterize obesity-prone animals. We therefore suggest that attention should be paid to the carbohydrate snacking and overall carbohydrate content in the diet during the last weeks (or months) preceding delivery to limit development of later metabolic disorders in offspring.

Food reward, hyperphagia, and obesity

Given the unabated obesity problem, there is increasing appreciation of expressions like "my eyes are bigger than my stomach," and recent studies in rodents and humans suggest that dysregulated brain reward pathways may be contributing not only to drug addiction but also to increased intake of palatable foods and ultimately obesity. After describing recent progress in revealing the neural pathways and mechanisms underlying food reward and the attribution of incentive salience by internal state signals, we analyze the potentially circular relationship between palatable food intake, hyperphagia, and obesity. Are there preexisting individual differences in reward functions at an early age, and could they be responsible for development of obesity later in life? Does repeated exposure to palatable foods set off a cascade of sensitization as in drug and alcohol addiction? Are reward functions altered by secondary effects of the obese state, such as increased signaling through inflammatory, oxidative, and mitochondrial stress pathways? Answering these questions will significantly impact prevention and treatment of obesity and its ensuing comorbidities as well as eating disorders and drug and alcohol addiction.

High-fat diet-induced obesity in animal models

Epidemiological studies have shown a positive relationship between dietary fat intake and obesity. Since rats and mice show a similar relationship, they are considered an appropriate model for studying dietary obesity. The present paper describes the history of using high-fat diets to induce obesity in animals, aims to clarify the consequences of changing the amount and type of dietary fats on weight gain, body composition and adipose tissue cellularity, and explores the contribution of genetics and sex, as well as the biochemical basis and the roles of hormones such as leptin, insulin and ghrelin in animal models of dietary obesity. The major factors that contribute to dietary obesity - hyperphagia, energy density and post-ingestive effects of the dietary fat - are discussed. Other factors that affect dietary obesity including feeding rhythmicity, social factors and stress are highlighted. Finally, we comment on the reversibility of high-fat diet-induced obesity.

Deficits in gastrointestinal responses controlling food intake and body weight

The gastrointestinal tract serves as a portal sensing incoming nutrients and relays mechanical and chemosensory signals of a meal to higher brain centers. Prolonged consumption of dietary fat causes adaptive changes within the alimentary, metabolic, and humoral systems that promote a more efficient process for energy metabolism from this rich source, leading to storage of energy in the form of adipose tissue. Furthermore, prolonged ingestion of dietary fats exerts profound effects on responses to signals involved in termination of a meal. This article reviews the effects of ingested fat on gastrointestinal motility, hormone release, and neuronal substrates. It focuses on changes in sensitivity to satiation signals resulting from chronic ingestion of high-fat diet, which may lead to disordered appetite and dysregulation of body weight.

Perilla leaf extract ameliorates obesity and dyslipidemia induced by high-fat diet

The objective of this study was to evaluate the antiobesity effect of perilla leaf extract (PLE) in animal models of high fat diet-induced obesity. C57BL/6J mice were fed a standard diet (STD) or high fat diet (HFD) for 5 weeks to induce obesity. The experimental groups were four groups with 10 mice per group and fed for 4 weeks: a STD group, a HFD group, a HFD containing 1% PLE (HFD+PLE 1%) group and a HFD containing 3% PLE (HFD+PLE 3%) group. The PLE supplementation significantly decreased body weight gain, food efficiency ratio, and relative liver and epididymal fat mass compared with those of the HFD group. Also, triglyceride, total cholesterol and LDL levels in the plasma were significantly reduced by PLE supplementation compared with the HFD group. Histological changes in the liver of the PLE supplemented group showed an inhibition of steatosis induced by HFD. Furthermore, PLE reversed the HFD induced changes in the expression patterns of epididymal adipose tissue genes: acetyl CoA carboxylase (ACC), glycerol-3-phosphate dehydrogenase (GPDH) and peroxisome proliferator-activated receptor gamma (PPARgamma). These results suggest that the PLE supplement suppressed body weight gain and improved the blood lipid profiling, in part by down-regulating adipogenic transcription factor and other specific target genes.

Flavor-nutrient learning is less rapid with fat than with carbohydrate in rats

Flavor-nutrient learning occurs when the post-ingestive consequences of a food are associated with its flavor. As a signal of the food's energy density, flavor-nutrient associations have the potential to contribute to the regulation of meal size. While all calorie sources (fat, carbohydrate, protein, ethanol) can support flavor-nutrient learning, prior research has found that flavor-nutrient associations based on fat may require higher nutrient concentrations and more rigorous experimental protocols than are required to train carbohydrate (cho)-based associations. To further explore potential macronutrient-specific differences in flavor-nutrient learning, the present study compared the time course of acquisition of cho- and fat-based associations. Rats were trained to associate distinctive flavors with high-density (3.2 kcal/mL) and low-density (0.2 kcal/mL) orally-consumed solutions, either fat (corn oil emulsion) or carbohydrate (sucrose). For each nutrient, both within- and between-group designs were used to assess (via two-bottle preference testing) whether flavor-nutrient learning had occurred after 2, 4, or 6 training trial pairs. Rats trained with carbohydrate demonstrated preferential intake of the low-density paired flavor after only 2 training pairs; in contrast, rats trained with fat required 6 training pairs. These findings demonstrate differential rapidity of acquisition flavor-nutrient associations. The longer time course of acquisition of fat-based flavor-nutrient associations may be yet another mechanism by which high-fat foods promote overeating.

CCK(1) receptor is essential for normal meal patterning in mice fed high fat diet

Cholecystokinin (CCK), released by lipid in the intestine, initiates satiety by acting at cholecystokinin type 1 receptors (CCK(1)Rs) located on vagal afferent nerve terminals located in the wall of the gastrointestinal tract. In the present study, we determined the role of the CCK(1)R in the short term effects of a high fat diet on daily food intake and meal patterns using mice in which the CCK(1)R gene is deleted. CCK(1)R(-/-) and CCK(1)R(+/+) mice were fed isocaloric high fat (HF) or low fat (LF) diets ad libitum for 18 h each day and meal size, meal frequency, intermeal interval, and meal duration were determined. Daily food intake was unaltered by diet in the CCK(1)R(-/-) compared to CCK(1)R(+/+) mice. However, meal size was larger in the CCK(1)R(-/-) mice compared to CCK(1)R(+/+) mice when fed a HF diet, with a concomitant decrease in meal frequency. Meal duration was increased in mice fed HF diet regardless of phenotype. In addition, CCK(1)R(-/-) mice fed a HF diet had a 75% decrease in the time to 1st meal compared to CCK(1)R(+/+) mice following a 6 h fast. These data suggest that lack of the CCK(1)R results in diminished satiation, causing altered meal patterns including larger, less frequent meals when fed a high fat diet. These results suggest that the CCK(1)R is involved in regulating caloric intake on a meal to meal basis, but that other factors are responsible for regulation of daily food intake.

Effects of red pepper on appetite and energy intake

Two studies were conducted to investigate the effects of red pepper (capsaicin) on feeding behaviour and energy intake. In the first study, the effects of dietary red pepper added to high-fat (HF) and high-carbohydrate (HC) meals on subsequent energy and macronutrient intakes were examined in thirteen Japanese female subjects. After the ingestion of a standardized dinner on the previous evening, the subjects ate an experimental breakfast (1883 kJ) of one of the following four types: (1) HF; (2) HF and red pepper (10 g); (3) HC; (4) HC and red pepper. Ad libitum energy and macronutrient intakes were measured at lunch-time. The HC breakfast significantly reduced the desire to eat and hunger after breakfast. The addition of red pepper to the HC breakfast also significantly decreased the desire to eat and hunger before lunch. Differences in diet composition at breakfast time did not affect energy and macronutrient intakes at lunch-time. However, the addition of red pepper to the breakfast significantly decreased protein and fat intakes at lunch-time. In Study 2, the effects of a red-pepper appetizer on subsequent energy and macronutrient intakes were examined in ten Caucasian male subjects. After ingesting a standardized breakfast, the subjects took an experimental appetizer (644 kJ) at lunch-time of one of the following two types: (1) mixed diet and appetizer; (2) mixed diet and red-pepper (6 g) appetizer. The addition of red pepper to the appetizer significantly reduced the cumulative ad libitum energy and carbohydrate intakes during the rest of the lunch and in the snack served several hours later. Moreover, the power spectral analysis of heart rate revealed that this effect of red pepper was associated with an increase in the ratio sympathetic: parasympathetic nervous system activity. These results indicate that the ingestion of red pepper decreases appetite and subsequent protein and fat intakes in Japanese females and energy intake in Caucasian males. Moreover, this effect might be related to an increase in sympathetic nervous system activity in Caucasian males.

Comparison of high-fat and high-carbohydrate foods in a meal or snack on short-term fat and energy intakes in obese women

The present study aimed to compare the action of high-fat and high-carbohydrate (CHO) foods on meal size (satiation) and post-meal satiety in obese women. A within-subjects design was used; each participant received all four nutritional challenges. Fifteen healthy obese women (age 21–56 years, BMI 35–48 kg/m2) participated; thirteen completed all four test days. On two test days, participants were exposed to a nutritional challenge comprising an ad libitum high-fat or high-CHO lunch. On the other two test days they were exposed to a challenge comprising an ad libitum sweet high-fat or high-CHO mid-afternoon snack. Energy and macronutrient intakes were measured at each eating episode. Visual analogue rating scales were completed periodically to record subjective feelings of appetite. When offered a high-CHO selection of foods at lunch and mid-afternoon participants consumed less energy than when offered a high-fat selection. However, post-meal satiety was similar. Total test-day energy intake was significantly higher when high-fat foods were consumed at lunch, but not as a snack. Consumption of high-fat foods at a lunch and snack increased the amount of fat consumed over the whole test day. In conclusion, energy intake of an eating episode was influenced by nutrient composition in this group of obese women. Consumption of high-fat foods at lunch or as a snack led to overconsumption relative to high-CHO foods. However, high-fat foods at meals may have greater potential to influence daily intake than at snacks, probably because meals are larger eating episodes and therefore give greater opportunity to overconsume.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Interactions between the "cognitive" and "metabolic" brain in the control of food intake

If the new environment and modern lifestyle cause obesity in individuals with thrifty genes by increasing energy intake, it is important to know by what mechanisms hyperphagia occurs and why energy balance is not kept in check by the homeostatic regulator. The argument is developed that procuring and ingesting food is an evolutionarily conserved survival mechanism that occupies large parts of the brain's computing capacity including not only the hypothalamus but also a number of cortico-limbic structures. These forebrain systems evolved to engage powerful emotions for guaranteed supply and ingestion of beneficial foods from a sparse and often hostile environment. They are now simply overwhelmed with an abundance of food and food cues that is no longer interrupted by frequent famines. After briefly reviewing structure and functions of the relevant cortico-limbic structures and the better-known hypothalamic homeostatic regulator, the review focuses mainly on interactions between the two systems. Although several cortico-limbic processes are sensitive to metabolic depletion and repletion signals, it appears that they are underlying the same reversible leptin resistance that renders hypothalamic circuits insensible to continuously high leptin levels during periods of feast. It is hypothesized that this naturally occurring leptin resistance allowed temporary neutralization of satiety mechanisms and evolved as a response to survive subsequent periods of famine. With today's continuous and abundant food availability for a segment of the population, the powerful cognitive processes to eat and the resulting overweight can partially escape negative feedback control in prone individuals most strongly expressing such thrifty genes.

Preference for palatable food is reduced by the gamma-hydroxybutyrate analogue GET73, in rats

Palatability and variety of foods are major reasons for "hedonic" eating, and hence for overeating and obesity. Palatable food and drugs of abuse share a common reward mechanism, and compounds that block the reinforcing effect of drugs of abuse preferentially suppress the intake of palatable foods. This research was aimed at studying the influence of the gamma-hydroxybutyrate analogue N-(4-trifluoromethylbenzyl)-4-methoxybutanamide (GET73) - that inhibits alcohol consumption - on consumption and reinforcing effect of palatable food. Adult male rats were used. For place preference conditioning, sweetened corn flakes were used as the reinforcer, and GET73 (50, 100 and 200mgkg(-1)) or vehicle were orally (p.o.) administered either 30min before each training session and the test session, or only before the test session. To study the influence on consumption, GET73 was given p.o. at the same doses once daily for 12 days to rats given free access to both palatable and varied food (cafeteria diet) or to standard chow. Both acquisition and expression of palatable food-induced conditioned place preference were inhibited by GET73, either administered throughout the conditioning period or only before the test session. GET73 reduced also the consumption of cafeteria food, while that of standard chow was increased. At these doses, GET73 had no detrimental effect on open-field behaviour. GET73 seems to specifically attenuate the gratification produced by varied and palatable food, without affecting the consumption of not particularly palatable chow. Since, overweight and obesity are mostly due to the overeating of palatable and varied foods, drugs like GET73 could represent a somewhat ideal and rational approach to obesity treatment.

Energy density and macronutrient composition determine flavor preference conditioned by intragastric infusions of mixed diets

In prior studies rats preferred a flavor (CS+HF) paired with intragastric (IG) infusions of a high-fat diet to a flavor (CS+HC) paired with a high-carbohydrate diet, yet just the opposite preference was observed with pure-nutrient infusions. The present study tested the hypothesis that variations in nutrient density as well as composition influence flavor learning. Animals were trained (22 h/day) with IG infusion of milk-based high-fat and high-carbohydrate liquid diets paired with intakes of flavored, noncaloric CS+ solutions. A third flavor, the CS-, was paired with water infusion. Standard chow was available ad libitum. The rats preferred both CS+ flavors to the CS-, whether the infused diets were dense (HF and HC, 2.1 kcal/ml) or dilute (hf and hc, 0.5 kcal/ml), indicating that all diet infusions were reinforcing. They consumed the CS+hc and CS+hf equally in training, and preferred the CS+hc, showing that at low-energy density carbohydrate was more reinforcing than fat. In contrast, CS+HF intake exceeded that of CS+HC in training, and the rats preferred the CS+HF to the CS+HC. In further tests the rats preferred the CS+HF to the CS+hc, the CS+HF to the CS+hf, and the CS+HC to the CS+hc; i.e., when the diets differed in energy density the flavors associated with the more concentrated infusions were preferred. In the absence of influence by flavor cues from the nutrients themselves, rats' preferences for flavors associated with diets high in fat or carbohydrate are dependent on energy density. The differential satiating effects of fat and carbohydrate may contribute to these density-dependent preferences.