Increased sensitivity to food cues in the fasted state and decreased inhibitory control in the satiated state in the overweight

Modality Matters: Fasted Individuals Inhibit Food Stimuli Better Than Neutral Stimuli for Words, but Not for Pictures

The current study aimed to evaluate the effect different modalities (pictures and words) of food stimuli have on inhibitory control under different homeostatic states. To this end, the homeostatic state was altered by asking participants to fast for 16 h (n = 67) or eat lunch as usual (n = 76) before completing an online stop-signal task with modal (pictures) and amodal (words) food and valenced-matched non-food stimuli. The inclusion of non-food stimuli allowed us to test the food specificity of the effect. We found a significant Group × Modality × Stimulus Type interaction (F(1,141) = 5.29, p = 0.023, ηp2 = 0.036): fasted individuals had similar inhibitory capacity for modal and amodal food stimuli but better inhibitory capacity for non-food words compared to images, while there were no inhibitory differences in dependence on either modality or stimulus type in satiated individuals. Thus, we were able to show that inhibitory capacities to modal compared to amodal stimuli depend on participants' current state of fasting. Future studies should focus on how this lowered inhibitory capacity influences food intake, as well as the role of stimulus valence in cognitive processing, to clarify potential implications for dieting and weight loss training.

The Cerebellar Response to Visual Portion Size Cues Is Associated with the Portion Size Effect in Children

The neural mechanisms underlying susceptibility to eating more in response to large portions (i.e., the portion size effect) remain unclear. Thus, the present study examined how neural responses to portion size relate to changes in weight and energy consumed as portions increase. Associations were examined across brain regions traditionally implicated in appetite control (i.e., an appetitive network) as well as the cerebellum, which has recently been implicated in appetite-related processes. Children without obesity (i.e., BMI-for-age-and-sex percentile < 90; N = 63; 55% female) viewed images of larger and smaller portions of food during fMRI and, in separate sessions, ate four meals that varied in portion size. Individual-level linear and quadratic associations between intake (kcal, grams) and portion size (i.e., portion size slopes) were estimated. The response to portion size in cerebellar lobules IV-VI was associated with the quadratic portion size slope estimated from gram intake; a greater response to images depicting smaller compared to larger portions was associated with steeper increases in intake with increasing portion sizes. Within the appetitive network, neural responses were not associated with portion size slopes. A decreased cerebellar response to larger amounts of food may increase children's susceptibility to overeating when excessively large portions are served.

Randomized Controlled Trial of Effects of Behavioral Weight Loss Treatment on Food Cue Reactivity

BACKGROUND

It is not known whether behavioral weight loss can attenuate blood oxygen level-dependent responses to food stimuli.

OBJECTIVES

This randomized controlled trial assessed the effects of a commercially available behavioral weight loss program (WW, WeightWatchers) compared to a wait-list control on blood oxygen level-dependent response to food cues.

METHODS

Females with obesity ( N = 61) were randomized to behavioral weight loss or wait-list control. At baseline and follow-up, participants completed assessments that included functional magnetic resonance imaging scans to assess response to images of high-calorie foods (HCF) or low-calorie foods (LCF), and neutral objects.

RESULTS

There were no significant between-group differences in change from baseline to follow-up in any regions of the brain in response to viewing HCF or LCF. From baseline to follow-up, participants in behavioral weight loss, compared with wait-list control, reported significantly greater increases in desire for LCF. Changes in liking and palatability of LCF and liking, palatability, and desire for HCF did not differ between groups.

DISCUSSION

Behavioral weight loss was associated with increased desire for LCF without changes in neural reactivity to food cues. These results suggest that alteration of neurological processes underlying responsiveness to food is difficult to achieve through behavioral weight management alone.

Spatiotemporal profile of altered neural reactivity to food images in obesity: Reward system is altered automatically and predicts efficacy of weight loss intervention

Introduction

Obesity presents a significant public health problem. Brain plays a central role in etiology and maintenance of obesity. Prior neuroimaging studies have found that individuals with obesity exhibit altered neural responses to images of food within the brain reward system and related brain networks. However, little is known about the dynamics of these neural responses or their relationship to later weight change. In particular, it is unknown if in obesity, the altered reward response to food images emerges early and automatically, or later, in the controlled stage of processing. It also remains unclear if the pretreatment reward system reactivity to food images is predictive of subsequent weight loss intervention outcome.

Methods

In this study, we presented high-calorie and low-calorie food, and nonfood images to individuals with obesity, who were then prescribed lifestyle changes, and matched normal-weight controls, and examined neural reactivity using magnetoencephalography (MEG). We performed whole-brain analysis to explore and characterize large-scale dynamics of brain systems affected in obesity, and tested two specific hypotheses: (1) in obese individuals, the altered reward system reactivity to food images occurs early and automatically, and (2) pretreatment reward system reactivity predicts the outcome of lifestyle weight loss intervention, with reduced activity associated with successful weight loss.

Results

We identified a distributed set of brain regions and their precise temporal dynamics that showed altered response patterns in obesity. Specifically, we found reduced neural reactivity to food images in brain networks of reward and cognitive control, and elevated reactivity in regions of attentional control and visual processing. The hypoactivity in reward system emerged early, in the automatic stage of processing (< 150 ms post-stimulus). Reduced reward and attention responsivity, and elevated neural cognitive control were predictive of weight loss after six months in treatment.

Discussion

In summary, we have identified, for the first time with high temporal resolution, the large-scale dynamics of brain reactivity to food images in obese versus normal-weight individuals, and have confirmed both our hypotheses. These findings have important implications for our understanding of neurocognition and eating behavior in obesity, and can facilitate development of novel integrated treatment strategies, including tailored cognitive-behavioral and pharmacological therapies.

Food-related reward sensitivity across the spectrum of body weight and impulsive eating: Pilot findings from a multi-method approach

Overweight with and without comorbid binge-eating disorder (BED) has been associated with increased reward sensitivity, though evidence is heterogeneous. To disentangle this heterogeneity and gain insights into mechanisms of impaired reward processing, this study applied multi-method neuro-behavioural techniques. Reward sensitivity was investigated in N = 49 participants allocated to three subgroups: overweight individuals with BED (BED+, n = 17), overweight individuals without BED (BED-, n = 15), and normal-weight controls (NWC, n = 17). Applying a free exploration paradigm (food vs. non-food stimuli), eye tracking and electroencephalographic data were gathered. A valid cue before stimulus onset indicated the position of food, and the end points analysed after the cue and stimulus onset were attentional approach, attention allocation, and conflict processing (e.g., conflict between looking at the potentially rewarding food stimulus or not). The effect of negative mood was tested using mood induction. The study's main hypothesis was that individuals with overweight, particularly under negative mood, would have increased food-related reward sensitivity. All participants showed increased food-specific attentional approach (p < .001). BED + allocated more attention to food stimuli than non-food stimuli compared to the healthy control (p = .045). For individuals with overweight but without BED (BED-), results indicate that conflict processing might be prolonged after the stimulus onset (p = .011). No group-specific effect of negative mood was found. Preliminary results in overweight individuals with and without comorbid BED suggest that food stimuli are generally rewarding stimuli, but even more so for participants with binge eating psychopathology. Prolonged conflict processing during the confrontation with competing food and non-food stimuli was solely found in the BED- sample and might indicate a compensation mechanism. Replication is warranted. The multi-method approach seems to be promising to give indications for the development of psychotherapeutic treatment.

A systematic review and meta-analyses of food preference modifications after bariatric surgery

This systematic review and meta-analyses aimed to synthesize evidence of the link between bariatric surgery and changes in food preferences, considering the method of assessment. MEDLINE, Cochrane Library, Web of Science, Cinahl, PsychINFO, ProQuest, and Open grey were searched incorporating two blocks of terms ("Intervention" and "Food Preferences"). Interventional or observational studies involving patients (BMI ≥ 35 kg m^-2 ) with sleeve gastrectomy (SG) or Roux-en-Y Gastric Bypass (RYGB) and a control group were included. Meta-analyses were performed comparing the standardized daily mean percentage energy from proteins, carbohydrates, and lipids between preoperative and postoperative patients. Fifty-seven studies concerning 2,271 patients with RYGB and 903 patients with SG met the inclusion criteria, of which 24 were eligible for meta-analysis. Despite a total reduction in macronutrient intakes, the meta-analyses revealed a postoperative increase in percentage energy from proteins at 12 months (0.24, 95% CI: 0.03, 0.46, {I² } = 73%) and a decrease in percentage energy from fat at 1 month (-0.47, 95% CI: 0.86, 0.09, {I² } = 72%), up to 24 months (-0.20, 95% CI: -0.31, 0.08, {I² } = 0%). In conclusion, the present systematic review and meta-analyses showed changes of food preferences in terms of macronutrient, food selection and, overall food appreciation up to 5 years following bariatric surgery.

Reassessing relationships between appetite and adiposity in people at risk of obesity: A twin study using fMRI

BACKGROUND

Neuroimaging studies suggest that appetitive drive is enhanced in obesity.

OBJECTIVE

To test if appetitive drive varies in direct proportion to the level of body adiposity after accounting for genetic factors that contribute to both brain response and obesity risk.

SUBJECTS/METHODS

Participants were adult monozygotic (n = 54) and dizygotic (n = 30) twins with at least one member of the pair with obesity. Body composition was assessed by dual-energy X-ray absorptiometry. Hormonal and appetite measures were obtained in response to a standardized meal that provided 20% of estimated daily caloric needs and to an ad libitum buffet meal. Pre- and post-meal functional magnetic resonance imaging (fMRI) assessed brain response to visual food cues in a set of a priori appetite-regulating regions. Exploratory voxelwise analyses outside a priori regions were performed with correction for multiple comparisons.

RESULTS

In a group of 84 adults, the majority with obesity (75%), body fat mass was not associated with hormonal responses to a meal (glucose, insulin, glucagon-like peptide-1 and ghrelin, all P>0.40), subjective feelings of hunger (β=-0.01 mm [95% CI -0.35, 0.34] P = 0.97) and fullness (β=0.15 mm [-0.15, 0.44] P = 0.33), or buffet meal intake in relation to estimated daily caloric needs (β=0.28% [-0.05, 0.60] P = 0.10). Body fat mass was also not associated with brain response to high-calorie food cues in appetite-regulating regions (Pre-meal β=-0.12 [-0.32, 0.09] P = 0.26; Post-meal β=0.18 [-0.02, 0.37] P = 0.09; Change by a meal β=0.29 [-0.02, 0.61] P = 0.07). Conversely, lower fat mass was associated with being weight reduced (β=-0.05% [-0.07, -0.03] P<0.001) and greater pre-meal activation to high-calorie food cues in the dorsolateral prefrontal cortex (Z = 3.63 P = 0.017).

CONCLUSIONS

In a large study of adult twins, the majority with overweight or obesity, the level of adiposity was not associated with excess appetitive drive as assessed by behavioral, hormonal, or fMRI measures.

Resting activity of the hippocampus and amygdala in obese individuals predicts their response to food cues

Obese individuals exhibit brain functional abnormalities in multiple regions implicated in reward/motivation, emotion/memory, homeostatic regulation, and executive control when exposed to food cues and during rest. However, it remains unclear whether abnormal brain responses to food cues might account for or relate to their abnormal activity in resting state. This information would be useful for understanding the neural mechanisms behind hyperactive responses to food cues, a critical marker of obesity. Resting-state functional magnetic resonance imaging (RS-fMRI) and a cue-reactivity fMRI task with high- (HiCal) and low-caloric (LoCal) food cues were employed to investigate brain baseline activity and food cue-induced activation differences in 44 obese participants (OB), in 37 overweight participants (OW), and in 37 normal weight (NW) controls. One-way analyses of variance showed there was a group difference in the left hippocampus/amygdala activity during resting state and during food-cue stimulation (p_FWE < 0.05); post-hoc tests showed the OB group had both greater basal activity and greater food cue-induced activation than the OW and NW groups; OW had higher activity in the hippocampus/amygdala than the NW group, which was only significant during resting state. In the OB group, resting-state activity in the left hippocampus/amygdala was positively correlated with activation induced by HiCal food cues, and both of these measures correlated with body mass index (BMI). Mediation analysis showed that the relationship between BMI and hippocampus/amygdala response to HiCal food cues was mediated by their resting-state activity. These findings suggest a close association between obesity and brain functional abnormality in the hippocampus/amygdala. They also indicate that resting-state activity in the hippocampus/amygdala may impact these regions' responses to food cues.

Visual food cues decrease blood glucose and glucoregulatory hormones following an oral glucose tolerance test in normal-weight and obese men

Previous experiments of our group have demonstrated that preprandial processing of food cues attenuates postprandial blood glucose excursions. Here we systematically re-evaluated the glucose-lowering effect of visual food cues by submitting 40 healthy fasted men (20 normal-weight men, mean age 24.8 ± 3.7 years, BMI 21.9 ± 0.3 kg/m²; 20 obese men, 26.8 ± 4.2 years, 34.3 ± 1.3 kg/m²) to an oral glucose tolerance test (OGTT) following exposure to pictures of high-calorie food items versus neutral items. OGTT-related changes in blood concentrations of glucose and relevant glucoregulatory hormones including GLP-1 were assessed and analyzed according to the oral minimal model. Independent of body weight, food-cue compared to neutral stimulus presentation reduced postprandial concentrations of glucose (p = 0.041), insulin (p = 0.026) and C-peptide (p = 0.007); accordingly, oral minimal model analyses yielded a food-cue induced decrease of dynamic-phase insulin secretion (p = 0.036). We also observed a trend towards lower GLP-1 levels directly after food cue stimulation in both body weight groups (p = 0.057), as well as a trend towards decreased heart rate (p = 0.093) and significantly decreased diastolic blood pressure (p = 0.019). While we did not detect indicators of an early rise in insulin levels in terms of a 'cephalic phase insulin response', our findings support the assumption that preprandial processing of food cues exerts marked effect on postprandial glucose regulation, with possible contributions of changes in GLP-1. The mechanisms linking food cue exposure and glucoregulatory improvements should be investigated in greater detail, to potentially open new treatment options for metabolic dysfunctions.

A plant-based meal affects thalamus perfusion differently than an energy- and macronutrient-matched conventional meal in men with type 2 diabetes, overweight/obese, and healthy men: A three-group randomized crossover study

BACKGROUND & AIMS

Reward circuitry in the brain plays a key role in weight regulation. We tested the effects of a plant-based meal on these brain regions.

METHODS

A randomized crossover design was used to test the effects of two energy- and macronutrient-matched meals: a vegan (V-meal) and a conventional meat (M-meal) on brain activity, gastrointestinal hormones, and satiety in participants with type 2 diabetes (T2D; n = 20), overweight/obese participants (O; n = 20), and healthy controls (H; n = 20). Brain perfusion was measured, using arterial spin labeling functional brain imaging; satiety was assessed using a visual analogue scale; and plasma concentrations of gut hormones were determined at 0 and 180 min. Repeated-measures ANOVA was used for statistical analysis. Bonferroni correction for multiple comparisons was applied. The Hedge's g statistic was used to measure the effect size for means of paired difference between the times (180-0 min) and meal types (M-V meal) for each group.

RESULTS

Thalamus perfusion was the highest in patients with T2D and the lowest in overweight/obese individuals (p = 0.001). Thalamus perfusion decreased significantly after ingestion of the M-meal in men with T2D (p = 0.04) and overweight/obese men (p = 0.004), and it decreased significantly after ingestion of the V-meal in healthy controls (p < 0.001; Group x Meal x Time: F = 3.4; p = 0.035). The effect size was -0.41 (95% CI, -1.14 to 0.31; p = 0.26) for men with diabetes; -0.72 (95% CI, -1.48 to 0.01; p = 0.05) for overweight/obese men; and 0.82 (95% CI, 0.09 to 1.59; p = 0.03) for healthy men. Postprandial secretion of active GLP-1 increased after the V-meal compared with the M-meal by 42% (95% CI 25-62%; p = 0.003) in men with T2D and by 41% (95% CI 24-61%; p = 0.002) in healthy controls. Changes in thalamus perfusion after ingestion of both test meals correlated with changes in satiety (r = +0.68; p < 0.01), fasting plasma insulin (r = +0.40; p < 0.01), C-peptide (r = +0.48; p < 0.01) and amylin (r = +0.55; p < 0.01), and insulin secretion at 5 mmol/l (r = +0.77; p < 0.05).

CONCLUSIONS

The higher postprandial GLP-1 secretion after the V-meal in men with T2D, with concomitant greater satiety and changes in thalamus perfusion, suggest a potential use of plant-based meals in addressing the key pathophysiologic mechanisms of food intake regulation. Trial registration ClinicalTrials.gov number, NCT02474147.

Preliminary evidence that endoscopic gastroplication reduces food reward

Morbidly obese patients are most successfully treated with bariatric surgery. Although restrictive gastric surgery physically limits food intake, it is also suggested that eating behavior and food-reward mechanisms are affected. Therefore, eating behavior and food-reward were assessed in ten patients that underwent gastric volume reduction by endoscopic gastroplication. Patients participated in test days before and one, three and twelve months after the procedure. Weight loss, food intake, appetite, gastric emptying rate, food-reward (i.e. liking and wanting) and eating behavior were assessed. Body mass index decreased from 38.3 (37.6-42.6) to 33.9 (31.0-35.9) kg/m² after one year. Ad libitum food intake decreased significantly after one month, but not after one year. Gastric emptying rate did not change. AUC of VAS scores for desire to eat, quantity, fullness, hunger, snacking and satiety changed after one month, but not all remained significantly changed after one year. Thirst did not change. Liking scores of food items decreased significantly in the fasted as well as the satiated state after the procedure. Wanting scores did not change. Uncontrolled eating decreased significantly after three and twelve months; emotional eating was only significantly decreased after three months. The results show that food intake decreases, while VAS scores for appetite and eating behavior change accordingly. Liking, but not wanting of food items changed to benefit the weight losing patient. The effects were stronger at one-month follow-up than at 12 months, which may be a risk of relapse after initial successful weight loss. The effects of new bariatric procedures on food-reward should be studied in future randomized trials to further elucidate their impact. REGISTERED AT CLINICALTRIALS. GOV: NCT02381340.

Challenging energy balance - during sensitivity to food reward and modulatory factors implying a risk for overweight - during body weight management including dietary restraint and medium-high protein diets

Energy balance is a key concept in the etiology and prevalence of obesity and its co-morbidities, as well as in the development of possible treatments. If energy intake exceeds energy expenditure, a positive energy balance develops and the risk for overweight, obesity, and its co-morbidities increases. Energy balance is determined by energy homeostasis, and challenged by sensitivity to food reward, and to modulatory factors such as circadian misalignment, high altitude, environmental temperature, and physical activity. Food reward and circadian misalignment increase the risk for overweight and obesity, while high altitude, changes in environmental temperature, or physical activity modulate energy balance in different directions. Modulations by hypobaric hypoxia, lowering environmental temperature, or increasing physical activity have been hypothesized to contribute to body weight loss and management, yet no clear evidence has been shown. Dietary approach as part of a lifestyle approach for body weight management should imply reduction of energy intake including control of food reward, thereby sustaining satiety and fat free body mass, sustaining energy expenditure. Green tea catechins and capsaicin in red pepper in part meet these requirements by sustaining energy expenditure and increasing fat oxidation, while capsaicin also suppresses hunger and food intake. Protein intake of at least 0,8 g/kg body weight meets these requirements in that it, during decreased energy intake, increases food intake control including control of food reward, and counteracts adaptive thermogenesis. Prevention of overweight and obesity is underscored by dietary restraint, implying control of sensitivity to challenges to energy balance such as food reward and circadian misalignment. Treatment of overweight and obesity may be possible using a medium-high protein diet (0,8-1,2 g/kg), together with increased dietary restraint, while controlling challenges to energy balance.

Oxytocin reduces the functional connectivity between brain regions involved in eating behavior in men with overweight and obesity

Background:

Oxytocin (OXT), shown to decrease food intake in animal models and men, is a promising novel treatment for obesity. We have shown that in men with overweight and obesity, intranasal (IN) OXT reduced the functional magnetic resonance imaging (fMRI) blood oxygenation level-dependent signal in the ventral tegmental area (VTA), the origin of the mesolimbic dopaminergic reward system, in response to high-calorie food vs. non-food images. Here, we employed functional connectivity fMRI analysis, which measures the synchrony in activation between neural systems in a context-dependent manner. We hypothesized that OXT would attenuate the functional connectivity of the VTA with key food motivation brain areas only when participants viewed high-calorie food stimuli.

Methods:

This randomized, double-blind, placebo-controlled crossover study of 24 IU IN OXT included 10 men with overweight or obesity (mean±SEM BMI: 28.9±0.8 kg/m²). Following drug administration, subjects completed an fMRI food motivation paradigm including images of high and low-calorie foods, non-food objects, and fixation stimuli. A psychophysiological interaction analysis was performed with the VTA as seed region.

Results:

Following OXT administration, compared with placebo, participants exhibited significantly attenuated functional connectivity between the VTA and the insula, oral somatosensory cortex, amygdala, hippocampus, operculum, and middle temporal gyrus in response to viewing high-calorie foods (Z≥3.1, cluster-corrected, p<0.05). There was no difference in functional connectivity between VTA and these brain areas when comparing OXT and placebo for low-calorie food, non-food, and fixation images.

Conclusion:

In men with overweight and obesity, OXT attenuates the functional connectivity between the VTA and food motivation brain regions in response to high-calorie visual food images. These findings could partially explain the observed anorexigenic effect of OXT, providing insight into the mechanism through which OXT ameliorates food cue-induced reward anticipation in patients with obesity. Additional studies are ongoing to further delineate the anorexigenic effect of OXT in obesity.

Verbesserung der Impuls- und Emotionsregulation bei Binge-Eating-Störungen

Zusammenfassung. Impulsivität beeinflusst die Verarbeitung von störungsspezifischen Reizen und die Handlungskompetenz hinsichtlich der Nahrungsaufnahme. Neuere Studien adressieren daher unterschiedliche Facetten impulsiven Erlebens und Verhaltens, um eine Reduktion von Essanfällen und des Körpergewichts bei der Binge-Eating-Störung (BES) zu erzielen. ImpulsE ist ein Therapieprogramm zur Verbesserung der Impuls- und Emotionsregulationsfertigkeiten, welches mit einem computergestützten nahrungsbezogenen Inhibitionstraining kombiniert und mit einer Standardbehandlung (TAU) verglichen wurde. N = 31 Personen mit BES nahmen teil (n = 22 ImpulsE, n = 9 TAU). Die Ergebnisse zeigten Verbesserungen in der nahrungsbezogenen Verhaltensinhibition und der allgemeinen Essstörungspathologie in beiden Gruppen, während sich die Anzahl von Essanfällen nur bei ImpulsE signifikant senkte. Die Ergebnisse stellen erste Hinweise auf die Wirksamkeit eines solchen Trainings dar. Eine Adaption an Jugendliche erscheint sinnvoll.

Impact of Hunger, Satiety, and Oral Glucose on the Association Between Insulin and Resting-State Human Brain Activity

To study the interplay of metabolic state (hungry vs. satiated) and glucose administration (including hormonal modulation) on brain function, resting-state functional magnetic resonance imaging (rs-fMRI) and blood samples were obtained in 24 healthy normal-weight men in a repeated measurement design. Participants were measured twice: once after a 36 h fast (except water) and once under satiation (three meals/day for 36 h). During each session, rs-fMRI and hormone concentrations were recorded before and after a 75 g oral dose of glucose. We calculated the amplitude map from blood-oxygen-level-dependent (BOLD) signals by using the fractional amplitude of low-frequency fluctuation (fALFF) approach for each volunteer per condition. Using multiple linear regression analysis (MLRA) the interdependence of brain activity, plasma insulin and blood glucose was investigated. We observed a modulatory impact of fasting state on intrinsic brain activity in the posterior cingulate cortex (PCC). Strikingly, differences in plasma insulin levels between hunger and satiety states after glucose administration at the time of the scan were negatively related to brain activity in the posterior insula and superior frontal gyrus (SFG), while plasma glucose levels were positively associated with activity changes in the fusiform gyrus. Furthermore, we could show that changes in plasma insulin enhanced the connectivity between the posterior insula and SFG. Our results indicate that hormonal signals like insulin alleviate an acute hemostatic energy deficit by modifying the homeostatic and frontal circuitry of the human brain.

Insulin resistance, weight, and behavioral variables as determinants of brain reactivity to food cues: a Prevention of Diabetes through Lifestyle Intervention and Population Studies in Europe and around the World - a PREVIEW study

Background

Obesity and type 2 diabetes have been linked to alterations in food reward processing, which may be linked to insulin resistance.

Objectives

In this clinical study, we investigated the respective contribution of insulin resistance, anthropometric measurements, and behavioral factors to brain reward activation in response to visual stimuli.

Design

Food reward-related brain reward activation was assessed with functional magnetic resonance imaging in 39 overweight or obese individuals with impaired fasting glucose, impaired glucose tolerance, or both [22 women, 17 men; mean ± SD insulin sensitivity index (ISI): 2.7 ± 1.3; body mass index (BMI; kg/m2): 32.3 ± 3.7; body fat percentage: 40.5% ± 7.9%; fasting glucose: 6.3 ± 0.6 mmol/L]. Food and nonfood images were shown in a randomized block design. Brain activation (food compared with nonfood images) was correlated with anthropometric and behavioral variables. Behavioral variables included eating behavior [Three-Factor Eating Questionnaire (TFEQ)] and habitual physical activity (Baecke). Glucose and insulin concentrations, determined during an oral-glucose challenge, were used to assess the homeostatic model assessment for insulin resistance (HOMA-IR) and Matsuda ISI.

Results

Food compared with nonfood brain activation was positively associated with HOMA-IR in the nucleus accumbens, right and left insula, and right cingulate gyrus (P < 0.005, corrected for multiple comparisons). TFEQ factor 2 was positively related to food compared with nonfood brain activation in the supramarginal gyrus (P < 0.005, corrected for multiple comparisons). Habitual physical activity during leisure time was negatively associated with food compared with nonfood brain activation in multiple regions associated with the attention and reward network (P < 0.005, corrected for multiple comparisons).

Conclusions

Individuals with increased insulin resistance and emotional eating or disinhibition showed higher brain reactivity to food cues, which may imply changes in food preference and hyperphagia. Individuals with higher habitual physical activity showed less food reward-related brain activation.

Associations of Brain Reactivity to Food Cues with Weight Loss, Protein Intake and Dietary Restraint during the PREVIEW Intervention

The objective was to assess the effects of a weight loss and subsequent weight maintenance period comprising two diets differing in protein intake, on brain reward reactivity to visual food cues. Brain reward reactivity was assessed with functional magnetic resonance imaging in 27 overweight/obese individuals with impaired fasting glucose and/or impaired glucose tolerance (HOMA-IR: 3.7 ± 1.7; BMI: 31.8 ± 3.2 kg/m²; fasting glucose: 6.4 ± 0.6 mmol/L) before and after an 8-week low energy diet followed by a 2-year weight maintenance period, with either high protein (HP) or medium protein (MP) dietary guidelines. Brain reactivity and possible relationships with protein intake, anthropometrics, insulin resistance and eating behaviour were assessed. Brain reactivity, BMI, HOMA-IR and protein intake did not change differently between the groups during the intervention. In the whole group, protein intake during weight maintenance was negatively related to changes in high calorie images>low calorie images (H > L) brain activation in the superior/middle frontal gyrus and the inferior temporal gyrus (p < 0.005, corrected for multiple comparisons). H > L brain activation was positively associated with changes in body weight and body-fat percentage and inversely associated with changes in dietary restraint in multiple reward, gustatory and processing regions (p < 0.005, corrected for multiple comparisons). In conclusion, changes in food reward-related brain activation were inversely associated with protein intake and dietary restraint during weight maintenance after weight loss and positively associated with changes in body weight and body-fat percentage.

Nutritional Health Considerations for Persons with Spinal Cord Injury

Chronic spinal cord injury (SCI) often results in morbidity and mortality due to all-cause cardiovascular disease (CVD) and comorbid endocrine disorders. Several component risk factors for CVD, described as the cardiometabolic syndrome (CMS), are prevalent in SCI, with the individual risks of obesity and insulin resistance known to advance the disease prognosis to a greater extent than other established risks. Notably, adiposity and insulin resistance are attributed in large part to a commonly observed maladaptive dietary/nutritional profile. Although there are no evidence-based nutritional guidelines to address the CMS risk in SCI, contemporary treatment strategies advocate more comprehensive lifestyle management that includes sustained nutritional guidance as a necessary component for overall health management. This monograph describes factors in SCI that contribute to CMS risks, the current nutritional profile and its contribution to CMS risks, and effective treatment strategies including the adaptability of the Diabetes Prevention Program (DPP) to SCI. Establishing appropriate nutritional guidelines and recommendations will play an important role in addressing the CMS risks in SCI and preserving optimal long-term health.

Influences of Hunger, Satiety and Oral Glucose on Functional Brain Connectivity: A Multimethod Resting-State fMRI Study

A major regulatory task of the organism is to keep brain functions relatively constant in spite of metabolic changes (e.g., hunger vs. satiety) or availability of energy (e.g., glucose administration). Resting-state functional magnetic resonance imaging (rs-fMRI) can reveal resulting changes in brain function but previous studies have focused mostly on the hypothalamus. Therefore, we took a whole-brain approach and examined 24 healthy normal-weight men once after 36 h of fasting and once in a satiated state (six meals over the course of 36 h). At the end of each treatment, rs-fMRI was recorded before and after the oral administration of 75 g of glucose. We calculated local connectivity (regional homogeneity [ReHo]), global connectivity (degree of centrality [DC]), and amplitude (fractional amplitude of low-frequency fluctuation [fALFF]) maps from the rs-fMRI data. We found that glucose administration reduced all measures selectively in the left supplementary motor area and increased ReHo and fALFF in the right middle and superior frontal gyri. For fALFF, we observed a significant interaction between metabolic states and glucose in the left thalamus. This interaction was driven by a fALFF increase after glucose treatment in the hunger relative to the satiety condition. Our results indicate that fALFF analysis is the most sensitive measure to detect effects of metabolic states on resting-state brain activity. Moreover, we show that multimethod rs-fMRI provides an unbiased approach to identify spontaneous brain activity associated with changes in homeostasis and caloric intake.

Greater Reward-Related Neuronal Response to Hedonic Foods in Women Compared with Men

OBJECTIVE

The current study aimed to identify how sex influences neurobiological responses to food cues, particularly those related to hedonic eating, and how this relates to obesity propensity, using functional magnetic resonance imaging (fMRI).

METHODS

Adult men and women who were either obesity resistant (OR) or obesity prone (OP) underwent fMRI while viewing visual food cues (hedonic foods, neutral foods, and nonfood objects) in both fasted and fed states.

RESULTS

When fasted, a significant sex effect on the response to hedonic vs. neutral foods was observed, with greater responses in women than men in the nucleus accumbens (P = 0.0002) and insula (P = 0.010). Sex-based differences were not observed in the fed state. No significant group effects (OP vs. OR) or group-by-sex interactions were observed in fasted or fed states.

CONCLUSIONS

Greater fasted responses to hedonic food cues in reward-related brain regions were observed in women compared with men, suggesting that women may be more sensitive to the reward value of hedonic foods than men when fasted. This may indicate sex-dependent neurophysiology underlying eating behaviors.

Theta-burst modulation of mid-ventrolateral prefrontal cortex affects salience coding in the human ventral tegmental area

In the context of hedonic (over-)eating the ventral tegmental area (VTA) as a core part of the dopaminergic reward system plays a central role in coding incentive salience of high-caloric food. In the present study, we used functional magnetic resonance imaging (fMRI) to investigate whether transcranial magnetic theta-burst stimulation (TBS) over the right mid-ventrolateral prefrontal cortex (mid-VLPFC) can induce modulation of calorie-sensitive brain activation in the VTA. The prefrontal location for TBS had been predetermined by seed-based resting-state fMRI with a functionally defined portion of the VTA serving as seed region obtained from an independent second fMRI experiment. In a sample of 15 healthy male participants, modulation of calorie-sensitive VTA activation did not significantly differ between the two TBS protocols. Comparisons with baseline revealed that both TBS protocols significantly affected calorie-sensitive neural processing of the mid-VLPFC in a rather similar way. In the VTA significant modulation of calorie-sensitive activation was observed after continuous TBS, whereas the modulatory effect of intermittent TBS was less reliable but also associated with a decrease of activation for high-caloric food images. Neurostimulation of right mid-VLPFC is suggestive as a main entry point of downstream signal changes for high- and low-caloric food cues that could enforce a shift in valuating stimuli of initially different incentive salience.

Food-Related Impulsivity in Obesity and Binge Eating Disorder-A Systematic Update of the Evidence

The specific eating pattern of Binge Eating Disorder (BED) patients has provoked the assumption that BED might represent a phenotype within the obesity spectrum that is characterized by increased impulsivity. Following the guidelines of the PRISMA statement (preferred reporting items for systematic reviews and meta-analyses), we here provide a systematic update on the evidence on food-related impulsivity in obese individuals, with and without BED, as well as normal-weight individuals. We separately analyzed potential group differences in the impulsivity components of reward sensitivity and rash-spontaneous behavior. Our search resulted in twenty experimental studies with high methodological quality. The synthesis of the latest evidence consolidates conclusions drawn in our initial systematic review that BED represents a distinct phenotype within the obesity spectrum that is characterized by increased impulsivity. Rash-spontaneous behavior in general, and specifically towards food, is increased in BED, while food-specific reward sensitivity is also increased in obese individuals without BED, but potentially to a lesser degree. A major next step for research entails the investigation of sub-domains and temporal components of inhibitory control in BED and obesity. Based on the evidence of impaired inhibitory control in BED, affected patients might profit from interventions that address impulsive behavior.

Resting state hypothalamic response to glucose predicts glucose-induced attenuation in the ventral striatal response to food cues

Feeding behavior is regulated by a complex interaction of central nervous system responses to metabolic signals that reflect nutrient availability and to food cues that trigger appetitive responses. Prior work has shown that the hypothalamus is a key brain area that senses and responds to changes in metabolic signals, and exposure to food cues induces the activation of brain areas involved in reward processing. However, it is not known how the hypothalamic responses to changes in metabolic state are related to reward responses to food cues. This study aimed to understand whether changes in hypothalamic activity in response to glucose-induced metabolic signals are linked to food-cue reactivity within brain areas involved in reward processing. We combined two neuroimaging modalities (Arterial Spin Labeling and Blood Oxygen Level Dependent) to measure glucose-induced changes in hypothalamic cerebral blood flow (CBF) and food-cue task induced changes in brain activity within reward-related regions. Twenty-five participants underwent a MRI session following glucose ingestion and a subset of twenty individuals underwent an additional water session on a separate day as a control condition (drink order randomized). Hunger was assessed before and after drink consumption. We observed that individuals who had a greater reduction in hypothalamic CBF exhibited a greater reduction in left ventral striatum food cue reactivity (Spearman's rho = 0.46, P = 0.048) following glucose vs. water ingestion. These results are the first to use multimodal imaging to demonstrate a link between hypothalamic metabolic signaling and ventral striatal food cue reactivity.

Body-Brain Connections: The Effects of Obesity and Behavioral Interventions on Neurocognitive Aging

Obesity is a growing public health problem in the United States, particularly in middle-aged and older adults. Although the key factors leading to a population increase in body weight are still under investigation, there is evidence that certain behavioral interventions can mitigate the negative cognitive and brain ("neurocognitive") health consequences of obesity. The two primary behaviors most often targeted for weight loss are caloric intake and physical activity. These behaviors might have independent, as well as overlapping/synergistic effects on neurocognitive health. To date obesity is often described independently from behavioral interventions in regards to neurocognitive outcomes, yet there is conceptual and mechanistic overlap between these constructs. This review summarizes evidence linking obesity and modifiable behaviors, such as physical activity and diet, with brain morphology (e.g., gray and white matter volume and integrity), brain function (e.g., functional activation and connectivity), and cognitive function across the adult lifespan. In particular, we review evidence bearing on the following question: Are associations between obesity and brain health in aging adults modifiable by behavioral interventions?

A new universal dynamic model to describe eating rate and cumulative intake curves

BACKGROUND

Attempts to model cumulative intake curves with quadratic functions have not simultaneously taken gustatory stimulation, satiation, and maximal food intake into account.

OBJECTIVE

Our aim was to develop a dynamic model for cumulative intake curves that captures gustatory stimulation, satiation, and maximal food intake.

DESIGN

We developed a first-principles model describing cumulative intake that universally describes gustatory stimulation, satiation, and maximal food intake using 3 key parameters: 1) the initial eating rate, 2) the effective duration of eating, and 3) the maximal food intake. These model parameters were estimated in a study (n = 49) where eating rates were deliberately changed. Baseline data was used to determine the quality of model's fit to data compared with the quadratic model. The 3 parameters were also calculated in a second study consisting of restrained and unrestrained eaters. Finally, we calculated when the gustatory stimulation phase is short or absent.

RESULTS

The mean sum squared error for the first-principles model was 337.1 ± 240.4 compared with 581.6 ± 563.5 for the quadratic model, or a 43% improvement in fit. Individual comparison demonstrated lower errors for 94% of the subjects. Both sex (P = 0.002) and eating duration (P = 0.002) were associated with the initial eating rate (adjusted R² = 0.23). Sex was also associated (P = 0.03 and P = 0.012) with the effective eating duration and maximum food intake (adjusted R² = 0.06 and 0.11). In participants directed to eat as much as they could compared with as much as they felt comfortable with, the maximal intake parameter was approximately double the amount. The model found that certain parameter regions resulted in both stimulation and satiation phases, whereas others only produced a satiation phase.

CONCLUSIONS

The first-principles model better quantifies interindividual differences in food intake, shows how aspects of food intake differ across subpopulations, and can be applied to determine how eating behavior factors influence total food intake.

Developmental differences in the brain response to unhealthy food cues: an fMRI study of children and adults

BACKGROUND

Food cues are omnipresent and may trigger overconsumption. In the past 2 decades, the prevalence of childhood obesity has increased dramatically. Because children's brains are still developing, especially in areas important for inhibition, children may be more susceptible than adults to tempting food cues.

OBJECTIVE

We examined potential developmental differences in children's and adults' responses to food cues to determine how these responses relate to weight status.

DESIGN

We included 27 children aged 10-12 y and 32 adults aged 32-52 y. Functional magnetic resonance imaging data were acquired during a food-viewing task in which unhealthy and healthy food pictures were presented.

RESULTS

Children had a stronger activation in the left precentral gyrus than did adults in response to unhealthy compared with healthy foods. In children, unhealthy foods elicited stronger activation in the right inferior temporal and middle occipital gyri, left precentral gyrus, bilateral opercular part of the inferior frontal gyrus, left hippocampus, and left middle frontal gyrus. Adults had stronger activation in the bilateral middle occipital gyrus and the right calcarine sulcus for unhealthy compared with healthy foods. Children with a higher body mass index (BMI) had lower activation in the bilateral dorsolateral prefrontal cortex while viewing unhealthy compared with healthy foods. In adults there was no correlation between BMI and neural response to unhealthy compared with healthy foods.

CONCLUSIONS

Unhealthy foods might elicit more attention both in children and in adults. Children had stronger activation while viewing unhealthy compared with healthy foods in areas involved in reward, motivation, and memory. Furthermore, children activated a motivation and reward area located in the motor cortex more strongly than did adults in response to unhealthy foods. Finally, children with a higher BMI had less activation in inhibitory areas in response to unhealthy foods, which may mean they are more susceptible to tempting food cues. This trial was registered at www.trialregister.nl as NTR4255.

Brain regions involved in ingestive behavior and related psychological constructs in people undergoing calorie restriction

Human food intake is regulated by physiological energy homeostatic mechanisms and hedonic mechanisms. These are affected by both very short-term and longer-term calorie restriction (CR). To date, there are parallel discussions in the literature that fail to integrate across these disciplines and topics. First, much of the available neuroimaging research focusses on specific functional paradigms (e.g. reward, energy homeostasis). These paradigms often fail to consider more complex and inclusive models that examine how potential brain regions of interest interact to influence ingestion. Second, the paradigms used focus primarily on short-term CR (fasting) which has limited generalizability to clinical application. Finally, the behavioral literature, while frequently examining longer-term CR and related psychological constructs in the context of weight management (e.g. hedonic restraint, 'liking', 'wanting' and food craving), fails to adequately tie these phenomena to underlying neural mechanisms. The result is a less than complete picture of the brain's role in the complexity of the human experience of ingestion. This disconnect highlights a major limitation in the CR literature, where attempts are persistently made to exert behavioral control over ingestion, without fully understanding the complex bio behavioral systems involved. In this review we attempt to summarize all potential brain regions important for human ingestion, present a broad conceptual overview of the brain's multifaceted role in ingestive behavior, the human (psychological) experiences related to ingestion and to examine how these factors differ according to three forms of CR. These include short-term fasting, extended CR, and restrained eating. We aim to bring together the neuroimaging literature with the behavioral literature within a conceptual framework that may inform future translational research.

Functional neuroimaging in obesity and the potential for development of novel treatments

Recently, exciting progress has been made in understanding the role of the CNS in controlling eating behaviour and in the development of overeating. Regions and networks of the human brain involved in eating behaviour and appetite control have been identified with neuroimaging techniques such as functional MRI, PET, electroencephalography, and magnetoencephalography. Hormones that regulate our drive to eat (eg, leptin, insulin, and glucagon-like peptide-1) can affect brain function. Defects in central hunger signalling are present in many pathologies. On the basis of an understanding of brain mechanisms that lead to overeating, powerful neuroimaging protocols could be a future clinical approach to allow individually tailored treatment options for patients with obesity. The aim of our Review is to provide an overview of neuroimaging approaches for obesity (ie, neuroimaging study design, questions which can be answered by neuroimaging, and limitations of neuroimaging techniques), examine current models of central nervous processes regulating eating behaviour, summarise and review important neuroimaging studies investigating therapeutic approaches to treat obesity or to control eating behaviour, and to provide a perspective on how neuroimaging might lead to new therapeutic approaches to obesity.

Brain imaging demonstrates a reduced neural impact of eating in obesity

OBJECTIVE

This study investigated functional brain response differences to food in women with BMI either <25 kg/m(2) (lean) or >35 kg/m(2) (severe obesity).

DESIGN AND METHODS

Thirty women, 18-65 years old, from academic medical centers participated. Baseline brain perfusion was measured with arterial spin labeling. Brain activity was measured via blood-oxygen-level-dependent functional magnetic resonance imaging in response to food cues, and appeal to cues was rated. Subjective hunger/fullness was reported pre- and post-imaging. After a standard meal, measures were repeated.

RESULTS

When fasting, brain perfusion did not differ significantly between groups; and both groups showed significantly increased activity in the neo- and limbic cortices and midbrain compared with baseline (P < 0.05, family-wise-error whole-brain corrected). Once fed, the lean group showed significantly decreased activation in these areas, especially the limbic cortex, whereas the group with severe obesity showed no such decreases (P < 0.05, family-wise-error whole-brain corrected). After eating, appeal ratings of food decreased only in lean women. Within groups, hunger decreased (P < 0.001) and fullness increased (P < 0.001) fasted to fed.

CONCLUSIONS

While fasting, brain response to food cues in women did not differ significantly despite BMI. After eating, brain activity quickly diminished in lean women but remained elevated in women with severe obesity. These brain activation findings confirm previous studies.

Differential effects of hunger and satiety on insular cortex and hypothalamic functional connectivity

The insula cortex and hypothalamus are implicated in eating behaviour, and contain receptor sites for peptides and hormones controlling energy balance. The insula encompasses multi‐functional subregions, which display differential anatomical and functional connectivities with the rest of the brain. This study aimed to analyse the effect of fasting and satiation on the functional connectivity profiles of left and right anterior, middle, and posterior insula, and left and right hypothalamus. It was hypothesized that the profiles would be altered alongside changes in homeostatic energy balance. Nineteen healthy participants underwent two 7‐min resting state functional magnetic resonance imaging scans, one when fasted and one when satiated. Functional connectivity between the left posterior insula and cerebellum/superior frontal gyrus, and between left hypothalamus and inferior frontal gyrus was stronger during fasting. Functional connectivity between the right middle insula and default mode structures (left and right posterior parietal cortex, cingulate cortex), and between right hypothalamus and superior parietal cortex was stronger during satiation. Differences in blood glucose levels between the scans accounted for several of the altered functional connectivities. The insula and hypothalamus appear to form a homeostatic energy balance network related to cognitive control of eating; prompting eating and preventing overeating when energy is depleted, and ending feeding or transferring attention away from food upon satiation. This study provides evidence of a lateralized dissociation of neural responses to energy modulations.

Disgust proneness and associated neural substrates in obesity

Defects in experiencing disgust may contribute to obesity by allowing for the overconsumption of food. However, the relationship of disgust proneness and its associated neural locus has yet to be explored in the context of obesity. Thirty-three participants (17 obese, 16 lean) completed the Disgust Propensity and Sensitivity Scale-Revised and a functional magnetic resonance imaging paradigm where images from 4 categories (food, contaminates, contaminated food or fixation) were randomly presented. Independent two-sample t-tests revealed significantly lower levels of Disgust Sensitivity for the obese group (mean score = 14.7) compared with the lean group (mean score = 17.6, P = 0.026). The obese group had less activation in the right insula than the lean group when viewing contaminated food images. Multiple regression with interaction analysis revealed one left insula region where the association of Disgust Sensitivity scores with activation differed by group when viewing contaminated food images. These interaction effects were driven by the negative correlation of Disgust Sensitivity scores with beta values extracted from the left insula in the obese group (r = -0.59) compared with a positive correlation in the lean group (r = 0.65). Given these body mass index-dependent differences in Disgust Sensitivity and neural responsiveness to disgusting food images, it is likely that altered Disgust Sensitivity may contribute to obesity.

Poor ability to resist tempting calorie rich food is linked to altered balance between neural systems involved in urge and self-control

Background

The loss of self-control or inability to resist tempting/rewarding foods, and the development of less healthful eating habits may be explained by three key neural systems: (1) a hyper-functioning striatum system driven by external rewarding cues; (2) a hypo-functioning decision-making and impulse control system; and (3) an altered insula system involved in the translation of homeostatic and interoceptive signals into self-awareness and what may be subjectively experienced as a feeling.

Methods

The present study examined the activity within two of these neural systems when subjects were exposed to images of high-calorie versus low-calorie foods using functional magnetic resonance imaging (fMRI), and related this activity to dietary intake, assessed by 24-hour recall. Thirty youth (mean BMI = 23.1 kg/m², range = 19.1 - 33.7; age =19.7 years, range = 14 - 22) were scanned using fMRI while performing food-specific go/nogo tasks.

Results

Behaviorally, participants more readily pressed a response button when go trials consisted of high-calorie food cues (HGo task) and less readily pressed the response button when go trials consisted of low-calorie food cues (LGo task). This habitual response to high-calorie food cues was greater for individuals with higher BMI and individuals who reportedly consume more high-calorie foods. Response inhibition to the high-calorie food cues was most difficult for individuals with a higher BMI and individuals who reportedly consume more high-calorie foods. fMRI results confirmed our hypotheses that (1) the "habitual" system (right striatum) was more activated in response to high-calorie food cues during the go trials than low-calorie food go trials, and its activity correlated with participants’ BMI, as well as their consumption of high-calorie foods; (2) the prefrontal system was more active in nogo trials than go trials, and this activity was inversely correlated with BMI and high-calorie food consumption.

Conclusions

Using a cross-sectional design, our findings help increase understanding of the neural basis of one’s loss of ability to self-control when faced with tempting food cues. Though the design does not permit inferences regarding whether the inhibitory control deficits and hyper-responsivity of reward regions are individual vulnerability factors for overeating, or the results of habitual overeating.

Electronic supplementary material

The online version of this article (doi:10.1186/1475-2891-13-92) contains supplementary material, which is available to authorized users.

Neural responses to visual food cues according to weight status: a systematic review of functional magnetic resonance imaging studies

Emerging evidence from recent neuroimaging studies suggests that specific food-related behaviors contribute to the development of obesity. The aim of this review was to report the neural responses to visual food cues, as assessed by functional magnetic resonance imaging (fMRI), in humans of differing weight status. Published studies to 2014 were retrieved and included if they used visual food cues, studied humans >18 years old, reported weight status, and included fMRI outcomes. Sixty studies were identified that investigated the neural responses of healthy weight participants (n = 26), healthy weight compared to obese participants (n = 17), and weight-loss interventions (n = 12). High-calorie food images were used in the majority of studies (n = 36), however, image selection justification was only provided in 19 studies. Obese individuals had increased activation of reward-related brain areas including the insula and orbitofrontal cortex in response to visual food cues compared to healthy weight individuals, and this was particularly evident in response to energy dense cues. Additionally, obese individuals were more responsive to food images when satiated. Meta-analysis of changes in neural activation post-weight loss revealed small areas of convergence across studies in brain areas related to emotion, memory, and learning, including the cingulate gyrus, lentiform nucleus, and precuneus. Differential activation patterns to visual food cues were observed between obese, healthy weight, and weight-loss populations. Future studies require standardization of nutrition variables and fMRI outcomes to enable more direct comparisons between studies.

Food-pics: an image database for experimental research on eating and appetite

Our current environment is characterized by the omnipresence of food cues. The sight and smell of real foods, but also graphically depictions of appetizing foods, can guide our eating behavior, for example, by eliciting food craving and influencing food choice. The relevance of visual food cues on human information processing has been demonstrated by a growing body of studies employing food images across the disciplines of psychology, medicine, and neuroscience. However, currently used food image sets vary considerably across laboratories and image characteristics (contrast, brightness, etc.) and food composition (calories, macronutrients, etc.) are often unspecified. These factors might have contributed to some of the inconsistencies of this research. To remedy this, we developed food-pics, a picture database comprising 568 food images and 315 non-food images along with detailed meta-data. A total of N = 1988 individuals with large variance in age and weight from German speaking countries and North America provided normative ratings of valence, arousal, palatability, desire to eat, recognizability and visual complexity. Furthermore, data on macronutrients (g), energy density (kcal), and physical image characteristics (color composition, contrast, brightness, size, complexity) are provided. The food-pics image database is freely available under the creative commons license with the hope that the set will facilitate standardization and comparability across studies and advance experimental research on the determinants of eating behavior.

Factors that influence the reinforcing value of foods and beverages

Behavioral economic principles state that as the cost of a product increases, purchasing or consumption of that product will decrease. To understand the impact of behavioral economics on ingestive behavior, our laboratory utilizes an operant behavior paradigm to measure how much work an individual will engage in to get access to foods and beverages. This task provides an objective measure of the reinforcing value. We have shown that consumption of the same high fat snack food every day for two weeks reduces its reinforcing value in lean individuals, but increases its reinforcing value in a subset of obese individuals. This increase in the reinforcing value of food predicts future weight gain. Similarly, we have shown that repeated intake of caffeinated soda increases its reinforcing value in boys, but not in girls. This increase in reinforcing value is not related to usual caffeine consumption, but may be associated with positive, subjective effects of caffeine that are more likely to be reported by boys than by girls. Because food and beverage reinforcement relates to real-world consumption, it is important to determine factors that increase or decrease the reinforcing value and determine the consequences of these responses. We are especially interested in determining ways to shift the behavioral economic curve in order to develop novel strategies to decrease the reinforcing value of less healthy snack foods and beverages, such as soda, potato chips and candy and to increase the reinforcing value of healthier foods and beverages, such as water, fruits, and vegetables.

The neural signature of satiation is associated with ghrelin response and triglyceride metabolism

Eating behavior is guided by a complex interaction between signals conveying information about energy stores, food availability, and palatability. How peripheral signals regulate brain circuits that guide feeding during sensation and consumption of a palatable food is poorly understood. We used fMRI to measure brain response to a palatable food (milkshake) when n=32 participants were fasted and fed with either a fixed-portion or ad libitum meal. We found that larger post-prandial reductions in ghrelin and increases in triglycerides were associated with greater attenuation of response to the milkshake in brain regions regulating reward and feeding including the midbrain, amygdala, pallidum, hippocampus, insula and medial orbitofrontal cortex. Satiation-induced brain responses to milkshake were not related to acute changes in circulating insulin, glucose, or free fatty acids. The impact of a meal on the response to milkshake in the midbrain and dorsolateral prefrontal cortex differed depending upon whether meal termination was fixed or volitional, irrespective of the amount of food consumed. We conclude that satiation-induced changes in brain response to a palatable food are strongly and specifically associated with changes in circulating ghrelin and triglycerides and by volitional meal termination.

Neural responses to subliminally presented cannabis and other emotionally evocative cues in cannabis-dependent individuals

RATIONALE

Addiction theories posit that drug-related cues maintain and contribute to drug use and relapse. Indeed, our recent study in cocaine-dependent patients demonstrated that subliminally presented cocaine-related stimuli activate reward neurocircuitry without being consciously perceived. Activation of reward neurocircuitry may provoke craving and perhaps prime an individual for subsequent drug-seeking behaviors.

OBJECTIVES

Using an equivalent paradigm, we tested whether cannabis cues activate reward neurocircuitry in treatment-seeking, cannabis-dependent individuals and whether activation was associated with relevant behavioral anchors: baseline cannabis craving (drug-seeking behavior) and duration of use (degree of conditioning).

METHODS

Twenty treatment-seeking, cannabis-dependent individuals (12 males) underwent event-related blood oxygen level-dependent functional magnetic resonance imaging during exposure to 33-ms cannabis, sexual, and aversive cues presented in a backward-masking paradigm. Drug use history and cannabis craving were assessed prior to imaging.

RESULTS

Participants showed increased activity to backward-masked cannabis cues in regions supporting reward detection and interoception, including the left anterior insula, left ventral striatum/amygdala, and right ventral striatum. Cannabis cue-related activity in the bilateral insula and perigenual anterior cingulate cortex was positively associated with baseline cannabis craving, and cannabis cue-related activity in the medial orbitofrontal cortex was positively correlated with years of cannabis use. Neural responses to backward-masked sexual cues were similar to those observed during cannabis cue exposure, while activation to aversive cues was observed only in the left anterior insula and perigenual anterior cingulate cortex.

CONCLUSIONS

These data highlight the sensitivity of the brain to subliminal reward signals and support hypotheses promoting a common pathway of appetitive motivation.

Neuroimaging of gastric distension and gastric bypass surgery

Several neuroimaging studies are presented, which derive from prior work on gastric distension. Using a nonsurgical approach, we inserted gastric balloons into rats, which led to a marked decrease in food intake that normalized at 8 weeks. Body weight, however, remained below controls, which encouraged pursuit of studies in humans. A gastric balloon was inserted in obese and lean subjects, and filled through a tube that led behind the subject with water to 0, 200, 400, 600, 800 mL, on different days prior to ingestion of a liquid meal. As gastric volume increased, intake decreased by about 40%. Stomach capacity was then investigated using a gastric balloon, by assessing subjective (maximal tolerance) and objective measures (gastric compliance). Obese individuals had a much larger stomach capacity than lean by both measures. Next, in a 2-month study, an indwelling gastric balloon was inflated to 400 mL for 1 month and deflated for 1 month in counterbalanced order. Body weight was reduced during the month when the balloon was inflated within the 2nd and 3rd week. The subsequent study involved fMRI in response to gastric distension of 0, 250, and 500 mL while the subject was in a scanner. Ratings of fullness, but not discomfort, increased at 500 mL. Amygdala and insula activation were associated with gastric distension. The amygdala, as part of the limbic system, is involved in emotion and reward, and the insula in interoception. The right amygdala activation was inversely related to BMI, consistent with greater gastric capacity at a higher BMI. The next fMRI study in obese and lean subjects used visual and auditory stimuli of high energy dense (ED) and low ED foods. Increased activation was observed in the midbrain, putamen, posterior cingulate gyrus, hippocampus, and superior temporal gyrus in the obese vs. lean group in response to high vs. low ED food cues. Several of these areas lie within the mesolimbic reward pathway, and greater activation to high ED foods in the obese, suggests they have increased reward-driven eating behavior. Lastly, an fMRI study using the same stimuli was conducted pre and post-gastric bypass surgery. There were postsurgical reductions in neural activity in mesolimbic areas including the prefrontal cortex, and to a greater degree for high ED than low ED cues, reflecting more normalized responses. Through the use of various methodologies, the stomach's influence on food intake, sensations of fullness, and brain activation is presented with suggestions for future research.

Is obesity a brain disease?

That the brain is involved in the pathogenesis and perpetuation of obesity is broadly self-intuitive, but traditional evaluation of this relationship has focused on psychological and environment-dependent issues, often referred to as the "it's all in the head" axiom. Here we review evidence that excessive nutrition or caloric flux, regardless of its primary trigger, elicits a biological trap which imprints aberrant energy control circuits that tend to worsen with the accumulation of body fat. Structural and functional changes in the brain can be recognized, such as hypothalamic inflammation and gliosis, reduction in brain volume, reduced regional blood flow or diminished hippocampal size. Such induced changes collectively translate into a vicious cycle of deranged metabolic control and cognitive deficits, some of which can be traced back even to childhood or adolescence. Much like other components of the obese state, brain disease is inseparable from obesity itself and requires better recognition to allow future therapeutic targeting.