Rats that binge eat fat-rich food do not show somatic signs or anxiety associated with opiate-like withdrawal: implications for nutrient-specific food addiction behaviors

Dietary fiber induces a fat preference associated with the gut microbiota

Eating behavior is essential to human health. However, whether future eating behavior is subjected to the conditioning of preceding dietary composition is unknown. This study aimed to investigate the effect of dietary fiber consumption on subsequent nutrient-specific food preferences between palatable high-fat and high-sugar diets and explore its correlation with the gut microbiota. C57BL/6NJcl male mice were subjected to a 2-week dietary intervention and fed either a control (n = 6) or inulin (n = 6) diet. Afterward, all mice were subjected to a 3-day eating behavioral test to self-select from the simultaneously presented high-fat and high-sugar diets. The test diet feed intakes were recorded, and the mice's fecal samples were analyzed to evaluate the gut microbiota composition. The inulin-conditioned mice exhibited a preference for the high-fat diet over the high-sugar diet, associated with distinct gut microbiota composition profiles between the inulin-conditioned and control mice. The gut microbiota Oscillospiraceae sp., Bacteroides acidifaciens, and Clostridiales sp. positively correlated with a preference for fat. Further studies with fecal microbiota transplantation and eating behavior-related neurotransmitter analyses are warranted to establish the causal role of gut microbiota on host food preferences. Food preferences induced by dietary intervention are a novel observation, and the gut microbiome may be associated with this preference.

Utility of 'substance use disorder' as a heuristic for understanding overeating and obesity

Rates of obesity and obesity-associated diseases have increased dramatically in countries with developed economies. Substance use disorders (SUDs) are characterized by the persistent use of the substance despite negative consequences. It has been hypothesized that overconsumption of palatable energy dense food can elicit SUD-like maladaptive behaviors that contribute to persistent caloric intake beyond homeostatic need even in the face of negative consequences. Palatable food and drugs of abuse act on many of the same motivation-related circuits in the brain, and can induce, at least superficially, similar molecular, cellular, and physiological adaptations on these circuits. As such, applying knowledge about the neurobiological mechanisms of SUDs may serve as useful heuristic to better understand the persistent overconsumption of palatable food that contributes to obesity. However, many important differences exist between the actions of drugs of abuse and palatable food in the brain. This warrants caution when attributing weight gain and obesity to the manifestation of a putative SUD-related behavioral disorder. Here, we describe similarities and differences between compulsive drug use in SUDs and overconsumption in obesity and consider the merit of the concept of "food addiction".

Is Food Addictive? A Review of the Science

As ultraprocessed foods (i.e., foods composed of mostly cheap industrial sources of dietary energy and nutrients plus additives) have become more abundant in our food supply, rates of obesity and diet-related disease have increased simultaneously. Food addiction has emerged as a phenotype of significant empirical interest within the past decade, conceptualized most commonly as a substance-based addiction to ultraprocessed foods. We detail (a) how approaches used to understand substance-use disorders may be applicable for operationalizing food addiction, (b) evidence for the reinforcing potential of ingredients in ultraprocessed foods that may drive compulsive consumptions, (c) the utility of conceptualizing food addiction as a substance-use disorder versus a behavioral addiction, and (d) clinical and policy implications that may follow if ultraprocessed foods exhibit an addictive potential. Broadly, the existing literature suggests biological and behavioral parallels between food addiction and substance addictions, with ultraprocessed foods high in both added fat and refined carbohydrates being most implicated in addictive-like eating. Future research priorities are also discussed, including the need for longitudinal studies and the potential negative impact of addictive ultraprocessed foods on children. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Turkish version of the Yale Food Addiction Scale: preliminary results of factorial structure, reliability, and construct validity

BACKGROUND

Yale Food Addiction Scale (YFAS) was established to identify individuals exhibiting signs of addiction towards certain types of food. This study aimed to develop a Turkish version of the Yale Food Addiction Scale and test its psychometric properties.

METHODS

The backward translation techniques were used to develop Turkish versions of the YFAS, and its reproducibility was assessed. Turkish version of the YFAS was administered to a total of 1033 participants (439 men and 594 women), aged 19-65 years. Exploratory factor analysis and confirmatory factor analysis were used to examine the factorial structure of the tool. Construct validity was assessed by principal component factor analysis with varimax rotation. Reliabilities were estimated with Cronbach's alpha coefficient. The criterion-related validity was tested by the administration of Eating Attitude Test-26 (EAT-26) to all participants.

RESULTS

The primary factor loadings for seven items were ranged between 0.45 and 0.79, and no items cross-loaded onto other factors. The fit indices showed that eight items of the YFAS were a good representation of the item responses and each item loaded significantly on the specified factor (p < 0.001 for each). YFAS subscales had a high internal consistency and test-retest reliability. The criterion-related validity of the tool showed a positive relationship with scales of the EAT-26.

CONCLUSION

Current study suggested that the Turkish version of the YFAS is a reliable, valid, and useful tool for assessing the signs of food addiction in a non-clinical sample.

Nutritional Contingency Reduces Alcohol Drinking by Altering Central Neurotransmitter Receptor Gene Expression in Rats

We have previously shown that 6 weeks of intermittent high-fat diet (Int-HFD) pre-exposure significantly reduced alcohol drinking in rats, providing preliminary evidence of the effectiveness of a dietary intervention in reducing alcohol intake. However, the functional framework and underlying neurobiological mechanisms of such dietary intervention are unknown. Here, we examined the impact of Int-HFD pre-exposure duration on alcohol drinking, plasma feeding peptides, and central neurotransmitter receptors gene expression. Male Long Evans rats (n = 6-7/group) received no pre-exposure, 1 or 2 weeks pre-exposure to Int-HFD and alcohol drinking (two-bottle choice) was evaluated. We observed HFD pre-exposure-dependent decrease in alcohol drinking, with a significant decrease observed following 2 weeks of Int-HFD pre-exposure. No significant between-group differences in plasma feeding peptides (i.e., ghrelin, leptin, insulin) were detected. A PCR array revealed that the expression of several neurotransmitter receptors was significantly (p < 0.05 and ≥2-fold) altered in the striatum and ventral tegmental area compared to controls. These data suggest that pre-exposure to a palatable diet is critical to reduce alcohol drinking in rats, possibly through genetic alterations in the brain reward circuitry. Importantly, the present study is a step forward in identifying the critical framework needed to evaluate the therapeutic potential of nutritional contingency in the management of alcoholism.

Behavioral profile of intermittent vs continuous access to a high fat diet during adolescence

Over the past few years, the effects of a high-fat diet (HFD) on cognitive functions have been broadly studied as a model of obesity, although no studies have evaluated whether these effects are maintained after the cessation of this diet. In addition, the behavioral effects of having a limited access to an HFD (binge-eating pattern) are mostly unknown, although they dramatically increase the vulnerability to drug use in contrast to having continuous access. Thus, the aim of the present study was to compare the effects of an intermittent versus a continuous exposure to an HFD during adolescence on cognition and anxiety-like behaviors, as well as to study the changes observed after the interruption of this diet. Adolescent male mice received for 40 days a standard diet, an HFD with continuous access or an HFD with sporadic limited access (2 h, three days a week). Two additional groups were fed with intermittent or continuous access to the HFD and withdrawn from this diet 15 days before the behavioral tests. Only the animals with a continuous access to the HFD showed higher circulating leptin levels, increased bodyweight, marked memory and spatial learning deficits, symptoms that disappeared after 15 days of HFD abstinence. Mice that binged on fat only showed hyperlocomotion, which normalized after 15 days of HFD cessation. However, discontinuation of fat, either in a binge or a continuous pattern, led to an increase in anxiety-like behavior. These results highlight that exposure to a high-fat diet during adolescence induces alterations in brain functions, although the way in which this diet is ingested determines the extent of these behavioral changes.

Food Addiction and Binge Eating: Lessons Learned from Animal Models

The feeding process is required for basic life, influenced by environment cues and tightly regulated according to demands of the internal milieu by regulatory brain circuits. Although eating behaviour cannot be considered "addictive" under normal circumstances, people can become "addicted" to this behaviour, similarly to how some people are addicted to drugs. The symptoms, cravings and causes of "eating addiction" are remarkably similar to those experienced by drug addicts, and both drug-seeking behaviour as eating addiction share the same neural pathways. However, while the drug addiction process has been highly characterised, eating addiction is a nascent field. In fact, there is still a great controversy over the concept of "food addiction". This review aims to summarize the most relevant animal models of "eating addictive behaviour", emphasising binge eating disorder, that could help us to understand the neurobiological mechanisms hidden under this behaviour, and to improve the psychotherapy and pharmacological treatment in patients suffering from these pathologies.

Food Addiction, High-Glycemic-Index Carbohydrates, and Obesity

BACKGROUND

Treatment success in obesity remains low, and recently food addiction has been delineated as an underlying etiologic factor with therapeutic relevance. Specifically, current treatment focuses on reduced food intake and increase of physical activity, whereas interventions for addiction encompass behavioral therapy, abstinence, and environmental interventions such as taxation, restrictions on advertising, and regulation of school menus.

CONTENT

Here, we reviewed the pertinent literature on food addiction with a specific focus on the role of high-glycemic-index carbohydrates in triggering addictive symptoms. Three lines of evidence support the concept of food addiction: (a) behavioral responses to certain foods are similar to substances of abuse; (b) food intake regulation and addiction rely on similar neurobiological circuits; (c) individuals suffering from obesity or addiction show similar neurochemical- and brain activation patterns.High-glycemic-index carbohydrates elicit a rapid shift in blood glucose and insulin levels, akin to the pharmacokinetics of addictive substances. Similar to drugs of abuse, glucose and insulin signal to the mesolimbic system to modify dopamine concentration. Sugar elicits addiction-like craving, and self-reported problem foods are rich in high-glycemic-index carbohydrates. These properties make high-glycemic-index carbohydrates plausible triggers for food addiction.

SUMMARY

We argue that food addiction is a plausible etiological factor contributing to the heterogeneous condition and phenotype of obesity. In at least a subset of vulnerable individuals, high-glycemic-index carbohydrates trigger addiction-like neurochemical and behavioral responses.

The importance of nutrition in aiding recovery from substance use disorders: A review

BACKGROUND

Nutrition is a prerequisite for health; yet, there is no special nutritional assessment or guidance for drug and alcohol dependent individuals, despite the fact that their food consumption is often very limited, risking malnutrition. Further, the premise is examined that malnutrition may promote drug seeking and impede recovery from substance use disorders (SUD).

METHOD

A narrative review addressed the relationship between substance use disorders and nutrition, including evidence for malnutrition, as well as their impact on metabolism and appetite regulation. The implications of the biopsychology of addiction and appetite for understanding the role of nutrition in SUD were also considered.

RESULTS

The literature overwhelmingly finds that subjects with alcohol use disorder (AUD) and drug use disorder (DUD) typically suffer from nutrient deficiencies. These nutrient deficiencies may be complicit in the alcoholic myopathy, osteopenia and osteoporosis, and mood disorders including anxiety and depression, observed in AUD and DUD. These same individuals have also been found to have altered body composition and altered hormonal metabolic regulators. Additionally, brain processes fundamental for survival are stimulated both by food, particularly sweet foods, and by substances of abuse, with evidence supporting confusion (addiction transfer) when recovering from SUD between cravings for a substance and craving for food.

CONCLUSION

Poor nutritional status in AUD and DUD severely impacts their physical and psychological health, which may impede their ability to resist substances of abuse and recover their health. This review contributes to a better understanding of interventions that could best support individuals with substance use disorders.

Changes in gene expression and sensitivity of cocaine reward produced by a continuous fat diet

RATIONALE

Preclinical studies report that free access to a high-fat diet (HFD) alters the response to psychostimulants.

OBJECTIVES

The aim of the present study was to examine how HFD exposure during adolescence modifies cocaine effects. Gene expression of CB1 and mu-opioid receptors (MOr) in the nucleus accumbens (N Acc) and prefrontal cortex (PFC) and ghrelin receptor (GHSR) in the ventral tegmental area (VTA) were assessed.

METHODS

Mice were allowed continuous access to fat from PND 29, and the locomotor (10 mg/kg) and reinforcing effects of cocaine (1 and 6 mg/kg) on conditioned place preference (CPP) were evaluated on PND 69. Another group of mice was exposed to a standard diet until the day of post-conditioning, on which free access to the HFD began.

RESULTS

HFD induced an increase of MOr gene expression in the N Acc, but decreased CB1 receptor in the N Acc and PFC. After fat withdrawal, the reduction of CB1 receptor in the N Acc was maintained. Gene expression of GHSR in the VTA decreased during the HFD and increased after withdrawal. Following fat discontinuation, mice exhibited increased anxiety, augmented locomotor response to cocaine, and developed CPP for 1 mg/kg cocaine. HFD reduced the number of sessions required to extinguish the preference and decreased sensitivity to drug priming-induced reinstatement.

CONCLUSION

Our results suggest that consumption of a HFD during adolescence induces neurobiochemical changes that increased sensitivity to cocaine when fat is withdrawn, acting as an alternative reward.

Intermittent access to a nutritionally complete high-fat diet attenuates alcohol drinking in rats

Binge eating disorder and alcohol use disorder (AUD) frequently co-occur in the presence of other psychiatric conditions. Data suggest that binge eating engages similar behavioral and neurochemical processes common to AUD, which might contribute to the etiology or maintenance of alcoholism. However, it is unclear how binge feeding behavior and alcohol intake interact to promote initiation or maintenance of AUD. We investigated the impact of binge-like feeding on alcohol intake and anxiety-like behavior in male Long Evans rats. Rats received chow (controls) or extended intermittent access (24h twice a week; Int-HFD) to a nutritionally complete high-fat diet for six weeks. Standard rodent chow was available ad-libitum to all groups and food intake was measured. Following HFD exposure, 20.0% ethanol, 2.0% sucrose intake and endocrine peptide levels were evaluated. Anxiety-like behavior was measured using a light-dark (LD) box apparatus. Rats in the Int-HFD group displayed a binge-like pattern of feeding (alternations between caloric overconsumption and voluntary caloric restriction). Surprisingly, alcohol intake was significantly attenuated in the Int-HFD group whereas sugar consumption was unaffected. Plasma acyl-ghrelin levels were significantly elevated in the Int-HFD group, whereas glucagon-like peptide-1 levels did not change. Moreover, rats in the Int-HFD group spent more time in the light side of the LD box compared to controls, indicating that binge-like feeding induced anxiolytic effects. Collectively, these data suggest that intermittent access to HFD attenuates alcohol intake through reducing anxiety-like behavior, a process potentially controlled by elevated plasma ghrelin levels.

Binge-like intake of HFD attenuates alcohol intake in rats

Binge eating and binge alcohol intake are behavioral manifestations of pathological feeding and alcohol use disorder (AUD), respectively. Binge-feeding and AUD have high comorbidity with other psychiatric disorders such as depression, which could have important implications for the management of these conditions. Importantly, these behaviors share many common features suggesting a singular etiology. However, the nature by which binge-feeding affects the development or maintenance of AUD is unclear. The present study examined the impact of a binge-feeding from a nutritionally complete high-fat diet (HFD) on initiation and maintenance of alcohol intake, anxiolytic behavior and central genetic changes in brain regions that control alcohol-reinforced behaviors. To do this, male Long-Evans rats received chow (controls) or HFD every three days (HFD-3D) or every day (HFD-ED) for 5weeks. Rodent chow and water were available ad-libitum to all groups throughout the experiment. Following 5weeks of HFD cycling, 20.0% ethanol or 2.0% sucrose intake was evaluated. In addition, anxiety-like behavior was measured using a light-dark box apparatus. Both HFD-3D and -ED groups of rats consumed significantly large amount of food during 2h HFD access sessions and reduced their chow intake in the next 22h. Surprisingly, binge-fed rats displayed attenuated acquisition of alcohol intake whereas sucrose consumption was unaffected. Rats exposed to HFD spent more time in the light side compared to chow controls, indicating that binge-feeding induced anxiolytic effects. In addition, alterations in the brain neurotensin system were observed following HFD exposure. These data indicate that binge-feeding behavior induces behavioral and genetic changes that help explain how alcohol intake is influenced by co-morbid eating disorders.

Sugar addiction: the state of the science

PURPOSE

As obesity rates continue to climb, the notion that overconsumption reflects an underlying 'food addiction' (FA) has become increasingly influential. An increasingly popular theory is that sugar acts as an addictive agent, eliciting neurobiological changes similar to those seen in drug addiction. In this paper, we review the evidence in support of sugar addiction.

METHODS

We reviewed the literature on food and sugar addiction and considered the evidence suggesting the addictiveness of highly processed foods, particularly those with high sugar content. We then examined the addictive potential of sugar by contrasting evidence from the animal and human neuroscience literature on drug and sugar addiction.

RESULTS

We find little evidence to support sugar addiction in humans, and findings from the animal literature suggest that addiction-like behaviours, such as bingeing, occur only in the context of intermittent access to sugar. These behaviours likely arise from intermittent access to sweet tasting or highly palatable foods, not the neurochemical effects of sugar.

CONCLUSION

Given the lack of evidence supporting it, we argue against a premature incorporation of sugar addiction into the scientific literature and public policy recommendations.

Endogenous opioids and feeding behavior: A decade of further progress (2004-2014). A Festschrift to Dr. Abba Kastin

Functional elucidation of the endogenous opioid system temporally paralleled the creation and growth of the journal, Peptides, under the leadership of its founding editor, Dr. Abba Kastin. He was prescient in publishing annual and uninterrupted reviews on Endogenous Opiates and Behavior that served as a microcosm for the journal under his stewardship. This author published a 2004 review, "Endogenous opioids and feeding behavior: a thirty-year historical perspective", summarizing research in this field between 1974 and 2003. The present review "closes the circle" by reviewing the last 10 years (2004-2014) of research examining the role of endogenous opioids and feeding behavior. The review summarizes effects upon ingestive behavior following administration of opioid receptor agonists, in opioid receptor knockout animals, following administration of general opioid receptor antagonists, following administration of selective mu, delta, kappa and ORL-1 receptor antagonists, and evaluating opioid peptide and opioid receptor changes in different food intake models.

Obesity and the neurocognitive basis of food reward and the control of intake

With the rising prevalence of obesity, hedonic eating has become an important theme in obesity research. Hedonic eating is thought to be that driven by the reward of food consumption and not metabolic need, and this has focused attention on the brain reward system and how its dysregulation may cause overeating and obesity. Here, we begin by examining the brain reward system and the evidence for its dysregulation in human obesity. We then consider the issue of how individuals are able to control their hedonic eating in the present obesogenic environment and compare 2 contrasting perspectives on the control of hedonic eating, specifically, enhanced control of intake via higher cognitive control and loss of control over intake as captured by the food addiction model. We conclude by considering what these perspectives offer in terms of directions for future research and for potential interventions to improve control over food intake at the population and the individual levels.

Sex differences in motivational responses to dietary fat in Syrian hamsters

Women are more likely than men to exhibit motivational disorders (e.g., anhedonia and anxiety) with limited treatment options, and to overconsume high-fat "comfort foods" to improve motivational disruptions. Unfortunately, neurobiological underpinnings for sex differences in motivational disruptions and their responses to dietary fat are poorly understood. To help bridge these fundamental knowledge gaps, we assessed behavioral and neurobiological responses to dietary fat in a hamster model of female-biased motivational lability. Relative to social housing, social separation reduced hedonic drive in a new behavioral assay, the reward investigational preference (RIP) test. Fluoxetine or desipramine treatment for 21, but not 7, days improved RIP test performance. Pharmacologic specificity in this test was shown by non-responsiveness to diazepam, tracazolate, propranolol, or naltrexone. In the anxiety-related feeding/exploration conflict (AFEC) test, social separation worsened latency to eat highly palatable food under anxiogenic conditions, but not in home cages. Social separation also reduced weight gain, food intake, and adiposity while elevating energy expenditure, assessed by caloric efficiency and indirect calorimetry. Furthermore, chronic high-fat feeding improved anhedonic and anxious responses to separation, particularly in females. In the motivation-influencing nucleus accumbens, females, but not males, exhibited a separation-induced anxiety-related decrease in Creb1 mRNA levels and an anhedonia-related decrease in ΔFosb mRNA levels. Consistent with its antidepressant- and anxiolytic-like effects on behavior, high-fat feeding elevated accumbal Creb1 and ΔFosb mRNA levels in females only. Another accumbal reward marker, Tlr4 mRNA, was elevated in females by high-fat feeding. These results show that social separation of hamsters provides a novel model of sex-dependent comorbid anhedonia, anxiety, and anorexia, and implicate accumbal CREB, ΔFosB, and TLR4. Moreover, the results validate a new assay for chronic antidepressant efficacy.

Food and addiction among the ageing population

Obesity among the elderly is a growing public health concern. Among the various factors that may contribute to the current rates of obesity is the rewarding aspect of highly palatable foods and beverages, which may lead to overconsumption and excess caloric intake. The present review describes recent research supporting the hypothesis that, for some individuals, the consumption these highly palatable foods and beverages may lead to the development of addictive-like behaviors. In particular, the authors consider the relevance of this hypothesis to the ageing population.

Gambling disorder and other behavioral addictions: recognition and treatment

Addiction professionals and the public are recognizing that certain nonsubstance behaviors--such as gambling, Internet use, video-game playing, sex, eating, and shopping--bear resemblance to alcohol and drug dependence. Growing evidence suggests that these behaviors warrant consideration as nonsubstance or "behavioral" addictions and has led to the newly introduced diagnostic category "Substance-Related and Addictive Disorders" in DSM-5. At present, only gambling disorder has been placed in this category, with insufficient data for other proposed behavioral addictions to justify their inclusion. This review summarizes recent advances in our understanding of behavioral addictions, describes treatment considerations, and addresses future directions. Current evidence points to overlaps between behavioral and substance-related addictions in phenomenology, epidemiology, comorbidity, neurobiological mechanisms, genetic contributions, responses to treatments, and prevention efforts. Differences also exist. Recognizing behavioral addictions and developing appropriate diagnostic criteria are important in order to increase awareness of these disorders and to further prevention and treatment strategies.

Animal models of compulsive eating behavior

Eating disorders are multifactorial conditions that can involve a combination of genetic, metabolic, environmental, and behavioral factors. Studies in humans and laboratory animals show that eating can also be regulated by factors unrelated to metabolic control. Several studies suggest a link between stress, access to highly palatable food, and eating disorders. Eating "comfort foods" in response to a negative emotional state, for example, suggests that some individuals overeat to self-medicate. Clinical data suggest that some individuals may develop addiction-like behaviors from consuming palatable foods. Based on this observation, "food addiction" has emerged as an area of intense scientific research. A growing body of evidence suggests that some aspects of food addiction, such as compulsive eating behavior, can be modeled in animals. Moreover, several areas of the brain, including various neurotransmitter systems, are involved in the reinforcement effects of both food and drugs, suggesting that natural and pharmacological stimuli activate similar neural systems. In addition, several recent studies have identified a putative connection between neural circuits activated in the seeking and intake of both palatable food and drugs. The development of well-characterized animal models will increase our understanding of the etiological factors of food addiction and will help identify the neural substrates involved in eating disorders such as compulsive overeating. Such models will facilitate the development and validation of targeted pharmacological therapies.

Overlap of food addiction and substance use disorders definitions: analysis of animal and human studies

Food has both homeostatic and hedonic components, which makes it a potent natural reward. Food related reward could therefore promote an escalation of intake and trigger symptoms associated to withdrawal, suggesting a behavioral parallel with substance abuse. Animal and human theoretical models of food reward and addiction have emerged, raising further interrogations on the validity of a bond between Substance Use Disorders, as clinically categorized in the DSM 5, and food reward. These models propose that highly palatable food items, rich in sugar and/or fat, are overly stimulating to the brain's reward pathways. Moreover, studies have also investigated the possibility of causal link between food reward and the contemporary obesity epidemic, with obesity being potentiated and maintained due to this overwhelming food reward. Although natural rewards are a hot topic in the definition and categorization of Substance Use Disorders, proofs of concept and definite evidence are still inconclusive. This review focuses on available results from experimental studies in animal and human models exploring the concept of food addiction, in an effort to determine if it depicts a specific phenotype and if there is truly a neurobiological similarity between food addiction and Substance Use Disorders. It describes results from sugar, fat and sweet-fat bingeing in rodent models, and behavioral and neurobiological assessments in different human populations. Although pieces of behavioral and neurobiological evidence supporting a food addiction phenotype in animals and humans are interesting, it seems premature to conclude on its validity.

Addicted to palatable foods: comparing the neurobiology of Bulimia Nervosa to that of drug addiction

RATIONALE

Bulimia nervosa (BN) is highly comorbid with substance abuse and shares common phenotypic and genetic predispositions with drug addiction. Although treatments for the two disorders are similar, controversy remains about whether BN should be classified as addiction.

OBJECTIVES

Here, we review the animal and human literature with the goal of assessing whether BN and drug addiction share a common neurobiology.

RESULTS

Similar neurobiological features are present following administration of drugs and bingeing on palatable food, especially sugar. Specifically, both disorders involve increases in extracellular dopamine (DA), D1 binding, D3 messenger RNA (mRNA), and ΔFosB in the nucleus accumbens (NAc). Animal models of BN reveal increases in ventral tegmental area (VTA) DA and enzymes involved in DA synthesis that resemble changes observed after exposure to addictive drugs. Additionally, alterations in the expression of glutamate receptors and prefrontal cortex activity present in human BN or following sugar bingeing in animals are comparable to the effects of addictive drugs. The two disorders differ in regards to alterations in NAc D2 binding, VTA DAT mRNA expression, and the efficacy of drugs targeting glutamate to treat these disorders.

CONCLUSIONS

Although additional empirical studies are necessary, the synthesis of the two bodies of research presented here suggests that BN shares many neurobiological features with drug addiction. While few Food and Drug Administration-approved options currently exist for the treatment of drug addiction, pharmacotherapies developed in the future, which target the glutamate, DA, and opioid systems, may be beneficial for the treatment of both BN and drug addiction.

Food consumption and weight gain after cessation of chronic amphetamine administration

Cessation of drug use often coincides with increased food consumption and weight gain in recovering addicts. However, it is not known whether this phenomenon (particularly the weight gain) is uniquely human, or whether it represents a consequence of drug cessation common across species. To address this issue, rats (n = 10/group) were given systemic injections of D-amphetamine (3 mg/kg) or an equal volume of saline vehicle for 9 consecutive days. Beginning 2 days after the final injection, rats were given free access to a highly palatable food mixture (consisting of sugar and butter) along with their standard chow diet, and food consumption and body weight were measured every 48 h for 30 days. Consistent with clinical observations, amphetamine-treated rats showed a greater increase in body weight over the course of the 30 days relative to vehicle-treated rats. Surprisingly, there was no difference in highly palatable food consumption between amphetamine- and vehicle-treated groups, but the amphetamine-treated group consumed significantly more standard chow than the control group. The finding that a history of chronic amphetamine exposure increases food consumption is consistent with previous work in humans showing that withdrawal from drugs of abuse is associated with overeating and weight gain. The current findings may reflect amphetamine-induced sensitization of mechanisms involved in reward motivation, suggesting that weight gain following drug cessation in humans could be due to similar mechanisms.

Hyperphagia: current concepts and future directions proceedings of the 2nd international conference on hyperphagia

OBJECTIVE

Hyperphagia is a central feature of inherited disorders (e.g., Prader-Willi Syndrome) in which obesity is a primary phenotypic component. Hyperphagia may also contribute to obesity as observed in the general population, thus raising the potential importance of common underlying mechanisms and treatments. Substantial gaps in understanding the molecular basis of inherited hyperphagia syndromes are present as are a lack of mechanistic of mechanistic targets that can serve as a basis for pharmacologic and behavioral treatments.

DESIGN AND METHODS

International conference with 28 experts, including scientists and caregivers, providing presentations, panel discussions, and debates.

RESULTS

The reviewed collective research and clinical experience provides a critical body of new and novel information on hyperphagia at levels ranging from molecular to population. Gaps in understanding and tools needed for additional research were identified.

CONCLUSIONS

This report documents the full scope of important topics reviewed at a comprehensive international meeting devoted to the topic of hyperphagia and identifies key areas for future funding and research.

A new biomarker of hedonic eating? A preliminary investigation of cortisol and nausea responses to acute opioid blockade

Overweight and obese individuals differ in their degree of hedonic eating. This may reflect adaptations in reward-related neural circuits, regulated in part by opioidergic activity. We examined an indirect, functional measure of central opioidergic activity by assessing cortisol and nausea responses to acute opioid blockade using the opioid antagonist naltrexone in overweight/obese women (mean BMI=31.1±4.8) prior to the start of a mindfulness-based intervention to reduce stress eating. In addition, we assessed indices of hedonic-related eating, including eating behaviors (binge eating, emotional eating, external eating, restraint) and intake of sweets/desserts and carbohydrates (Block Food Frequency); interoceptive awareness (which is associated with dysregulated eating behavior); and level of adiposity at baseline. Naltrexone-induced increases in cortisol were associated with greater emotional and restrained eating and lower interoceptive awareness. Naltrexone-induced nausea was associated with binge eating and higher adiposity. Furthermore, in a small exploratory analysis, naltrexone-induced nausea predicted treatment response to the mindfulness intervention, as participants with more severe nausea at baseline maintained weight whereas those with little or no nausea responses tended to gain weight. These preliminary data suggest that naltrexone-induced cortisol release and nausea may help identify individuals who have greater underlying food reward dependence, which leads to an excessive drive to eat. Future research is needed to confirm this finding and to test if these markers of opioidergic tone might help predict success in certain types of weight management programs.

A high-fat diet or galanin in the PVN decreases phosphorylation of CREB in the nucleus accumbens

A high-fat diet (HFD) can increase hypothalamic galanin (GAL). GAL has recently been shown to inhibit opiate reward, which in turn, decreases cAMP response element-binding protein (CREB) in the nucleus accumbens (NAc). We hypothesized that injection of GAL into the paraventricular nucleus (PVN), or consumption of a HFD, would be associated with a decrease in NAc CREB. In Exp. 1, GAL in the PVN of naïve rats decreased phosphorylated-CREB (pCREB) which is the activated form of CREB, in the NAc compared to saline-injected controls. In Exp. 2, rats fed ad libitum HFD for 4 weeks had reduced NAc pCREB levels compared to rats with sporadic tastes of the HFD. Body weight, serum triglyceride and leptin levels were also raised in the chronic HFD-fed rats. These data suggest that PVN GAL or chronic intake of a HFD can decrease NAc pCREB. The implications of these findings may help to explain the lack of opiate-like withdrawal that has been reported in response to overeating a HFD, thereby providing a potential mechanism underlying behavioral differences seen with addiction-like overconsumption of different types of palatable foods.

From passive overeating to "food addiction": a spectrum of compulsion and severity

A psychobiological dimension of eating behaviour is proposed, which is anchored at the low end by energy intake that is relatively well matched to energy output and is reflected by a stable body mass index (BMI) in the healthy range. Further along the continuum are increasing degrees of overeating (and BMI) characterized by more severe and more compulsive ingestive behaviours. In light of the many similarities between chronic binge eating and drug abuse, several authorities have adopted the perspective that an apparent dependence on highly palatable food-accompanied by emotional and social distress-can be best conceptualized as an addiction disorder. Therefore, this review also considers the overlapping symptoms and characteristics of binge eating disorder (BED) and models of food addiction, both in preclinical animal studies and in human research. It also presents this work in the context of the modern and "toxic" food environment and therein the ubiquitous triggers for over-consumption. We complete the review by providing evidence that what we have come to call "food addiction" may simply be a more acute and pathologically dense form of BED.

Dopamine and food addiction: lexicon badly needed

Over the last few years, the concept of food addiction has become a common feature in the scientific literature, as well as the popular press. Nevertheless, the use of the term addiction to describe pathological aspects of food intake in humans remains controversial, and even among those who affirm the validity of the concept, there is considerable disagreement about its utility for explaining the increasing prevalence of obesity throughout much of the world. An examination of the literature on food addiction indicates that mesolimbic and nigrostriatal dopamine systems often are cited as mechanisms that contribute to the establishment of food addiction. However, in reviewing this literature, it is important to have a detailed consideration of the complex nature of dopaminergic involvement in motivational processes. For example, although it is often stated that mesolimbic dopamine mediates reward, there is no standard or consistent technical meaning of this term. Moreover, there is a persistent tendency to link dopamine transmission with pleasure or hedonia, as opposed to other aspects of motivation or learning. The present article provides a critical discussion of some aspects of the food addiction literature, viewed through the lens of recent findings and current theoretical views of dopaminergic involvement in food motivation. Furthermore, compulsive food intake and binge eating will be considered from an evolutionary perspective, in terms of the motivational subsystems that are involved in adaptive patterns of food consumption and seeking behaviors and a consideration of how these could be altered in pathological conditions.

Intermittent access to sweet high-fat liquid induces increased palatability and motivation to consume in a rat model of binge consumption

Binge eating disorders are characterized by discrete episodes of rapid and excessive food consumption. In rats, giving intermittent access to sweet fat food mimics this aspect of binge eating. These models typically employ solid food; however, the total amount consumed depends on motivation, palatability and satiety, which are difficult to dissociate with solid food. In contrast, lick microstructure analysis can be used to dissociate these parameters when the ingestant is a liquid. Therefore, we developed a binge model using a liquid emulsion composed of corn oil, heavy cream and sugar. We show that rats given intermittent access to this high-fat emulsion develop binge-like behavior comparable to that previously observed with solid high-fat food. One feature of this behavior was a gradual escalation in consumption across 2.5 weeks of intermittent access, which was not apparent in rats given lower-fat liquid on the same access schedule. Lick microstructure analysis suggests that this escalation was due at least in part to increases in both motivation to consume and palatability-driven consumption.

Is food addiction a valid and useful concept?

In this paper, we consider the concept of food addiction from a clinical and neuroscientific perspective. Food addiction has an established and growing currency in the context of models of overeating and obesity, and its acceptance shapes debate and research. However, we argue that the evidence for its existence in humans is actually rather limited and, in addition, there are fundamental theoretical difficulties that require consideration. We therefore review food addiction as a phenotypic description, one that is based on overlap between certain eating behaviours and substance dependence. To begin, we consider limitations in the general application of this concept to obesity. We share the widely held view that such a broad perspective is not sustainable and consider a more focused view: that it underlies particular eating patterns, notably binge eating. However, even with this more specific focus, there are still problems. Validation of food addiction at the neurobiological level is absolutely critical, but there are inconsistencies in the evidence from humans suggesting that caution should be exercised in accepting food addiction as a valid concept. We argue the current evidence is preliminary and suggest directions for future work that may provide more useful tests of the concept.

The contribution of brain reward circuits to the obesity epidemic

One of the defining characteristics of the research of Ann E. Kelley was her recognition that the neuroscience underlying basic learning and motivation processes also shed significant light upon mechanisms underlying drug addiction and maladaptive eating patterns. In this review, we examine the parallels that exist in the neural pathways that process both food and drug reward, as determined by recent studies in animal models and human neuroimaging experiments. We discuss contemporary research that suggests that hyperphagia leading to obesity is associated with substantial neurochemical changes in the brain. These findings verify the relevance of reward pathways for promoting consumption of palatable, calorically dense foods, and lead to the important question of whether changes in reward circuitry in response to intake of such foods serve a causal role in the development and maintenance of some cases of obesity. Finally, we discuss the potential value for future studies at the intersection of the obesity epidemic and the neuroscience of motivation, as well as the potential concerns that arise from viewing excessive food intake as an "addiction". We suggest that it might be more useful to focus on overeating that results in frank obesity, and multiple health, interpersonal, and occupational negative consequences as a form of food "abuse".

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

Effects of CB1 and CRF1 receptor antagonists on binge-like eating in rats with limited access to a sweet fat diet: lack of withdrawal-like responses

Positive reinforcement (e.g., appetitive, rewarding properties) has often been hypothesized to maintain excessive intake of palatable foods. Recently, rats receiving intermittent access to high sucrose diets showed binge-like intake with withdrawal-like signs upon cessation of access, suggesting negative reinforcement mechanisms contribute as well. Whether intermittent access to high fat diets also produces withdrawal-like syndromes is controversial. The present study therefore tested the hypothesis that binge-like eating and withdrawal-like anxiety would arise in a novel model of binge eating based on daily 10-min access to a sweet fat diet (35% fat kcal, 31% sucrose kcal). Within 2-3 weeks, female Wistar rats developed binge-like intake comparable to levels seen previously for high sucrose diets (~40% of daily caloric intake within 10 min) plus excess weight gain and adiposity, but absent increased anxiety-like behavior during elevated plus-maze or defensive withdrawal tests after diet withdrawal. Binge-like intake was unaffected by pretreatment with the corticotropin-releasing factor type 1 (CRF(1)) receptor antagonist R121919, and corticosterone responses to restraint stress did not differ between sweet-fat binge rats and chow-fed controls. In contrast, pretreatment with the cannabinoid type 1 (CB(1)) receptor antagonist SR147778 dose-dependently reduced binge-like intake, albeit less effectively than in ad lib chow or sweet fat controls. A priming dose of the sweet fat diet did not precipitate increased anxiety-like behavior, but rather increased plus-maze locomotor activity. The results suggest that CB(1)-dependent positive reinforcement rather than CRF(1)-dependent negative reinforcement mechanisms predominantly maintain excessive intake in this limited access model of sweet-fat diet binges.

Obesity and the brain: how convincing is the addiction model?

An increasingly influential perspective conceptualizes both obesity and overeating as a food addiction accompanied by corresponding brain changes. Because there are far-reaching implications for clinical practice and social policy if it becomes widely accepted, a critical evaluation of this model is important. We examine the current evidence for the link between addiction and obesity, identifying several fundamental shortcomings in the model, as well as weaknesses and inconsistencies in the empirical support for it from human neuroscientific research.

Further developments in the neurobiology of food and addiction: update on the state of the science

Over the past three decades, obesity has become a major public health crisis in the United States. The prevalence of obesity in the United States and in other parts of the world has led to a new word, "globesity," being used to describe the problem. As a result of this increased emphasis on understanding the causes and consequences of obesity, novel theories have stimulated new research aimed to prevent, intervene in and ameliorate the effects and decrease the incidence and medical consequences of globesity. One theory that has gained popularity in recent years, is based on the idea that an excessive intake of highly palatable foods shares similarities with the effects on brain and behavior that are seen with some drugs of abuse. Although this theory is not new, empirically-based translational research has only recently provided strong support for this hypothesis. In the present article, we review the present state of the science in this area and describe some newer clinical and preclinical works that shed light on innovative and interesting overlaps between excessivly palatable food intake and drug use.