Sex-based differences in the behavioral and neuronal responses to food

Ageing diminishes the modulation of human brain responses to visual food cues by meal ingestion

BACKGROUND/OBJECTIVES

Rates of obesity are greatest in middle age. Obesity is associated with altered activity of brain networks sensing food-related stimuli and internal signals of energy balance, which modulate eating behaviour. The impact of healthy mid-life ageing on these processes has not been characterised. We therefore aimed to investigate changes in brain responses to food cues, and the modulatory effect of meal ingestion on such evoked neural activity, from young adulthood to middle age.

SUBJECTS/METHODS

Twenty-four healthy, right-handed subjects, aged 19.5-52.6 years, were studied on separate days after an overnight fast, randomly receiving 50 ml water or 554 kcal mixed meal before functional brain magnetic resonance imaging while viewing visual food cues.

RESULTS

Across the group, meal ingestion reduced food cue-evoked activity of amygdala, putamen, insula and thalamus, and increased activity in precuneus and bilateral parietal cortex. Corrected for body mass index, ageing was associated with decreasing food cue-evoked activation of right dorsolateral prefrontal cortex (DLPFC) and precuneus, and increasing activation of left ventrolateral prefrontal cortex (VLPFC), bilateral temporal lobe and posterior cingulate in the fasted state. Ageing was also positively associated with the difference in food cue-evoked activation between fed and fasted states in the right DLPFC, bilateral amygdala and striatum, and negatively associated with that of the left orbitofrontal cortex and VLPFC, superior frontal gyrus, left middle and temporal gyri, posterior cingulate and precuneus. There was an overall tendency towards decreasing modulatory effects of prior meal ingestion on food cue-evoked regional brain activity with increasing age.

CONCLUSIONS

Healthy ageing to middle age is associated with diminishing sensitivity to meal ingestion of visual food cue-evoked activity in brain regions that represent the salience of food and direct food-associated behaviour. Reduced satiety sensing may have a role in the greater risk of obesity in middle age.

High-fat diet-related stimulation of sweetness desire is greater in women than in men despite high vegetable intake

OBJECTIVE

To examine the effects of lunches with different dietary energy densities on food preferences between genders.

DESIGN

Randomized crossover study. Participants were administered the following packed test meals once weekly on a specified day during six sessions: control (150 g of rice with a sautéed beef entrée containing 40 g of raw beef and 240 g of vegetables), high-meat/low-rice, low-vegetable, medium-fat/low-vegetable, high-fat and high-fat/low-vegetable meals. Subjective levels of sensory properties were assessed over time using visual analogue scales.

SETTING

University of Tokushima Graduate School, Tokushima, Japan.

SUBJECTS

Sixty-five men and sixty-five women matched by age and BMI.

RESULTS

Men showed significantly stronger desires for salty and fatty foods after meals (P<0.05). Women showed a significantly stronger desire for sweetness from 2 h after the low-vegetable meal, and increasing fat content under high-vegetable conditions caused a significant stimulated sweetness desire in women more than in men (P<0.05). Moreover, after a high-meat/low-rice meal with 100 g of rice, sweetness desire was stronger in women (P=0.024), whereas no significant differences in sweetness desire were shown between genders after another low-energy-density control meal with 150 g of rice.

CONCLUSIONS

Men had significantly stronger desires for salty and fatty foods, whereas women preferred sweet food after meals. The sweetness desire in women was stimulated by increasing fat content, even with a high vegetable intake. Low rice intake in a low-energy-density diet also caused a relative stimulation of sweetness desire in women.

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.

Inhibitory control effects in adolescent binge eating and consumption of sugar-sweetened beverages and snacks

Inhibitory control and sensitivity to reward are relevant to the food choices individuals make frequently. An imbalance of these systems can lead to deficits in decision-making that are relevant to food ingestion. This study evaluated the relationship between dietary behaviors - binge eating and consumption of sweetened beverages and snacks - and behavioral control processes among 198 adolescents, ages 14 to 17. Neurocognitive control processes were assessed with the Iowa Gambling Task (IGT), a generic Go/No-Go task, and a food-specific Go/No-Go task. The food-specific version directly ties the task to food cues that trigger responses, addressing an integral link between cue-habit processes. Diet was assessed with self-administered food frequency and binge eating questionnaires. Latent variable models revealed marked gender differences. Inhibitory problems on the food-specific and generic Go/No-Go tasks were significantly correlated with binge eating only in females, whereas inhibitory problems measured with these tasks were the strongest correlates of sweet snack consumption in males. Higher BMI percentile and sedentary behavior also predicted binge eating in females and sweet snack consumption in males. Inhibitory problems on the generic Go/No-Go, poorer affective decision-making on the IGT, and sedentary behavior were associated with sweetened beverage consumption in males, but not females. The food-specific Go/No-Go was not predictive in models evaluating sweetened beverage consumption, providing some initial discriminant validity for the task, which consisted of sweet/fatty snacks as no-go signals and no sugar-sweetened beverage signals. This work extends research findings, revealing gender differences in inhibitory function relevant to behavioral control. Further, the findings contribute to research implicating the relevance of cues in habitual behaviors and their relationship to snack food consumption in an understudied population of diverse adolescents not receiving treatment for eating disorders.

Ventral frontal satiation-mediated responses to food aromas in obese and normal-weight women

BACKGROUND

Sensory properties of foods promote and guide consumption in hunger states, whereas satiation should dampen the sensory activation of ingestive behaviors. Such activation may be disordered in obese individuals.

OBJECTIVE

Using functional magnetic resonance imaging (fMRI), we studied regional brain responses to food odor stimulation in the sated state in obese and normal-weight individuals targeting ventral frontal regions known to be involved in coding for stimulus reward value.

DESIGN

Forty-eight women (25 normal weight; 23 obese) participated in a 2-day (fed compared with fasting) fMRI study while smelling odors of 2 foods and an inedible, nonfood object. Analyses were conducted to permit an examination of both general and sensory-specific satiation (satiation effects specific to a given food).

RESULTS

Normal-weight subjects showed significant blood oxygen level-dependent responses in the ventromedial prefrontal cortex (vmPFC) to food aromas compared with responses induced by the odor of an inedible object. Normal-weight subjects also showed general (but not sensory-specific) satiation effects in both the vmPFC and orbitofrontal cortex. Obese subjects showed no differential response to the aromas of food and the inedible object when fasting. Within- and between-group differences in satiation were driven largely by changes in the response to the odor of the inedible stimulus. Responses to food aromas in the obese correlated with trait negative urgency, the tendency toward negative affect-provoked impulsivity.

CONCLUSIONS

Ventral frontal signaling of reward value may be disordered in obesity, with negative urgency heightening responses to food aromas. The observed nature of responses to food and nonfood stimuli suggests that future research should independently quantify each to fully understand brain reward signaling in obesity.

Bran fibers and satiety in women who do not exhibit restrained eating

BACKGROUND

Foods that are high in dietary fiber can promote satiety, but previous studies report conflicting results.

OBJECTIVE

The objective was to determine differences in satiety response to three conditions (10 g oat bran, 10 g barley bran and a low fiber condition) consumed at dinner and breakfast. In addition, we compared energy intake at an ad libitum lunch after consumption of the breakfast bars.

DESIGN

Randomized, double-blind crossover study.

PARTICIPANTS/SETTING

42 normal weight women.

INTERVENTION

Women consumed a dinner food bar from one of the three conditions the evening before testing. On test mornings, fasted women consumed the corresponding breakfast food bar with their choice of coffee, tea or water. An ad libitum pizza lunch was served 4 hours after breakfast.

PRIMARY OUTCOMES

Visual analogue scales (VAS) were used to assess satiety at baseline, 15, 30, 45, 60, 90, 120, 180 and 240 minutes. Energy intake was assessed by an ad libitum pizza lunch (4 hours after breakfast) and 24-hour energy intake was measured by a food diary.

STATISTICAL ANALYSES

Treatments were compared using the mixed-effects linear models. Outcomes are reported as mean ± SEM.

RESULTS

There were no significant differences among conditions on any of the satiety scales and no significant differences among conditions in energy consumed at lunch or over 24 hours. The fiber bars were well tolerated and no significant differences were found for gastrointestinal tolerance.

CONCLUSIONS

Our results do not support an effect of bran fibers on satiety above a low fiber control. We acknowledge results of this study may be intricately tied to the choice of a single pizza lunch, as other ad libitum meal options could have resulted in different outcomes.

Sexually dimorphic functional connectivity in response to high vs. low energy-dense food cues in obese humans: an fMRI study

Sexually-dimorphic behavioral and biological aspects of human eating have been described. Using psychophysiological interaction (PPI) analysis, we investigated sex-based differences in functional connectivity with a key emotion-processing region (amygdala, AMG) and a key reward-processing area (ventral striatum, VS) in response to high vs. low energy-dense (ED) food images using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in obese persons in fasted and fed states. When fed, in response to high vs. low-ED food cues, obese men (vs. women) had greater functional connectivity with AMG in right subgenual anterior cingulate, whereas obese women had greater functional connectivity with AMG in left angular gyrus and right primary motor areas. In addition, when fed, AMG functional connectivity with pre/post-central gyrus was more associated with BMI in women (vs. men). When fasted, obese men (vs. women) had greater functional connectivity with AMG in bilateral supplementary frontal and primary motor areas, left precuneus, and right cuneus, whereas obese women had greater functional connectivity with AMG in left inferior frontal gyrus, right thalamus, and dorsomedial prefrontal cortex. When fed, greater functional connectivity with VS was observed in men in bilateral supplementary and primary motor areas, left postcentral gyrus, and left precuneus. These sex-based differences in functional connectivity in response to visual food cues may help partly explain differential eating behavior, pathology prevalence, and outcomes in men and women.

Sweet lies: neural, visual, and behavioral measures reveal a lack of self-control conflict during food choice in weight-concerned women

Despite their intentions, weight-concerned individuals generally fail to control their eating behavior. However, it is unknown whether this failure is due to a lack of effortful self-control, or to not experiencing an internal conflict between weight goals and food temptations. The present study used fMRI, eye tracking and reaction times to assess the degree of conflict experienced by weight-concerned women during food choices that posed either a self-control dilemma (i.e., requiring a choice between healthy and palatable foods), or not. Contrary to the common assumption in self-control theory that food choices posing a self-control dilemma evoke internal conflict, we found that choices requiring self-control induced no conflict, as demonstrated by lower reaction times, fixation durations, number of gaze switches between snacks, and lower activation of the anterior cingulate cortex. Our results suggest that self-control failure might be due to a lack of experienced conflict, rather than to failing to act upon the perception of such conflict. This implies that effectiveness of weight maintenance interventions might be improved if they also focus on increasing the ability to detect a self-control dilemma, in addition to the current focus on increasing self-regulatory capacity.

A functional neuroimaging review of obesity, appetitive hormones and ingestive behavior

Adequate energy intake is vital for the survival of humans and is regulated by complex homeostatic and hedonic mechanisms. Supported by functional MRI (fMRI) studies that consistently demonstrate differences in brain response as a function of weight status during exposure to appetizing food stimuli, it has been posited that hedonically driven food intake contributes to weight gain and obesity maintenance. These food reward theories of obesity are reliant on the notion that the aberrant brain response to food stimuli relates directly to ingestive behavior, specifically, excess food intake. Importantly, functioning of homeostatic neuroendocrine regulators of food intake, such as leptin and ghrelin, are impacted by weight status. Thus, data from studies that evaluate the effect on weight status on brain response to food may be a result of differences in neuroendocrine functioning and/or behavior. In the present review, we examine the influence of weight and weight change, exogenous administration of appetitive hormones, and ingestive behavior on BOLD response to food stimuli.

Influence of shiftwork on greek nursing personnel

Background

The aim of this study was to investigate the burden experienced by nursing personnel working irregular shifts in Greece and to conduct the first test of a Greek version of the Standard Shiftwork Index (SSI).

Methods

A cross-sectional survey was carried out. The SSI was completed by 365 nurses and nursing assistants working shifts, including nights.

Results

Female nursing personnel and those suffering from a chronic disease were most affected by working rotating shifts as they had elevated scores on the majority of the SSI scales, such as sleep, chronic fatigue, digestive and cardiovascular problems, general health questionnaire, cognitive and somatic anxiety, shift time satisfaction, engagement and disengagement strategies, languidity, flexibility, and neurotisicm. Nurses with longer working experience and those with family responsibilities also scored higher on some of the SSI scales, such as the sleep, shift time satisfaction, social and domestic disruption, disengagement strategies, morningness, and languidity scales.

Conclusion

Shiftwork affects female nurses, those with chronic disease, older age, and domestic responsibilities more severely. Therefore management should take these factors into account when designing work schedules to alleviate the burden caused by shiftwork.

Neural systems underlying the reappraisal of personally craved foods

Craving of unhealthy food is a common target of self-regulation, but the neural systems underlying this process are understudied. In this study, participants used cognitive reappraisal to regulate their desire to consume idiosyncratically craved or not craved energy-dense foods, and neural activity during regulation was compared with each other and with the activity during passive viewing of energy-dense foods. Regulation of both food types elicited activation in classic top-down self-regulation regions including the dorsolateral prefrontal, inferior frontal, and dorsal anterior cingulate cortices. This main effect of regulation was qualified by an interaction, such that activation in these regions was significantly greater during reappraisal of craved (versus not craved) foods and several regions, including the dorsolateral prefrontal, inferior frontal, medial frontal, and dorsal anterior cingulate cortices, were uniquely active during regulation of personally craved foods. Body mass index significantly negatively correlated with regulation-related activation in the right dorsolateral PFC, thalamus, and bilateral dorsal ACC and with activity in nucleus accumbens during passive viewing of craved (vs. neutral, low-energy density) foods. These results suggest that several of the brain regions involved in the self-regulation of food craving are similar to other kinds of affective self-regulation and that others are sensitive to the self-relevance of the regulation target.

Abdominal fat is associated with a greater brain reward response to high-calorie food cues in Hispanic women

OBJECTIVE

Exposure to high-calorie foods may promote overeating by stimulating brain reward pathways and appetite. Abdominal fat has particularly adverse metabolic consequences and may alter brain pathways that regulate feeding behavior. Functional magnetic resonance imaging (fMRI) was used to test the hypothesis that high-calorie food cues activate brain reward regions and increase appetite, and to examine the relationship between abdominal fat and brain reward responsiveness in Hispanic women.

DESIGN AND METHODS

fMRI was performed while 13 volunteers viewed 12 blocks of pictures of food and non-food items. Participants rated hunger and food desire after each block of pictures. Brain activation to high-calorie foods was determined by calculating a contrast of high-calorie food minus non-food images. Pearson's correlations were used to test the relationship between brain reward activation and waist circumference.

RESULTS

High-calorie food images activated brain reward regions (Z > 2.3, P < 0.05 corrected for multiple comparisons) and increased hunger (P = 0.001), desire for sweet (P = 0.012) and savory (P = 0.009) foods. The striatal response to high-calorie foods positively correlated with waist circumference, independent of BMI (r = 0.621, P = 0.031).

CONCLUSIONS

Exposure to high-calorie food images activates brain reward pathways and increases appetitive drive in Hispanic females. Abdominal fat, independent of BMI, parallels striatal responsiveness to high-calorie food images.

Sex differences in the physiology of eating

Hypothalamic-pituitary-gonadal (HPG) axis function fundamentally affects the physiology of eating. We review sex differences in the physiological and pathophysiological controls of amounts eaten in rats, mice, monkeys, and humans. These controls result from interactions among genetic effects, organizational effects of reproductive hormones (i.e., permanent early developmental effects), and activational effects of these hormones (i.e., effects dependent on hormone levels). Male-female sex differences in the physiology of eating involve both organizational and activational effects of androgens and estrogens. An activational effect of estrogens decreases eating 1) during the periovulatory period of the ovarian cycle in rats, mice, monkeys, and women and 2) tonically between puberty and reproductive senescence or ovariectomy in rats and monkeys, sometimes in mice, and possibly in women. Estrogens acting on estrogen receptor-α (ERα) in the caudal medial nucleus of the solitary tract appear to mediate these effects in rats. Androgens, prolactin, and other reproductive hormones also affect eating in rats. Sex differences in eating are mediated by alterations in orosensory capacity and hedonics, gastric mechanoreception, ghrelin, CCK, glucagon-like peptide-1 (GLP-1), glucagon, insulin, amylin, apolipoprotein A-IV, fatty-acid oxidation, and leptin. The control of eating by central neurochemical signaling via serotonin, MSH, neuropeptide Y, Agouti-related peptide (AgRP), melanin-concentrating hormone, and dopamine is modulated by HPG function. Finally, sex differences in the physiology of eating may contribute to human obesity, anorexia nervosa, and binge eating. The variety and physiological importance of what has been learned so far warrant intensifying basic, translational, and clinical research on sex differences in eating.

Effect of polydextrose and soluble maize fibre on energy metabolism, metabolic profile and appetite control in overweight men and women

High-fibre diets offer several beneficial health effects. The objective of the present study was to investigate whether replacement of 30 % of the available carbohydrates with polydextrose (PDX) or soluble maize fibre (SCF) at breakfast and lunch would result in an increased fat oxidation rate and satiety, which may be of relevance for body weight control and diabetes prevention. In a single-blind, randomised cross-over study, eighteen overweight men and women underwent four different dietary interventions, which consisted of a PDX diet, a SCF diet and two control diets (full energetic and isoenergetic, comparable with PDX with respect to g or energy percentage of macronutrients, respectively). Glycaemic profile, energy expenditure and substrate oxidation were measured for 24 h in a respiration chamber. Circulating insulin, NEFA and TAG concentrations were determined over a 14 h period during daytime. Appetite ratings were assessed using visual analogue scales. The replacement of available carbohydrates with PDX or SCF reduced the peak glucose response, which was accompanied by reduced postprandial insulin responses. Moreover, higher concentrations of circulating NEFA were observed after consumption of both fibre diets, which were accompanied by an increased fat oxidation over 24 h. This effect was mainly attributed to the lower energetic value of the fibre diets and not to the fibres per se. Besides increasing fat oxidation, PDX exerted a pronounced suppressive effect on appetite ratings. The replacement of available carbohydrates with PDX may be of special interest because of its beneficial effects on metabolic profile and it may affect body weight control in the long term.

Children's reward responses to picture- and odor-cued food stimuli: a developmental analysis between 6 and 11years

The reward system is largely involved in the control of food intake. Whether components of this system (i.e., wanting and liking) change during development remains understudied, as well as how proximate factors (sensory cues, motivational state) modulate reward reactivity across development. We examined the developmental pattern of wanting and liking for sensorily-cued food stimuli in 6-11year old children as a function of the child's motivational state (hunger/satiety), gender, and the nature of foods. School children were exposed before or after their lunch on alternative days to visual and odor stimuli representing different categories of familiar foods. Their task was to rate wanting and liking of pictures and odorants of pizza, meat, vegetables, fruits, and chocolate. The following results were found: (1) While liking appeared to be stable from age 6 to 11, more particularly for visually-cued foods, wanting decreased, as well as did subjective hunger perception; (2) there were smaller or absent state-effects in 7-to-9-year-olds; (3) reward ratings were higher in boys than in girls; (4) reward ratings of vegetables were the lowest at all ages. These results suggest that wanting, but not liking, is developmentally variable over childhood, and that this variation depends on age, gender, motivational state (hunger/satiety), the nature of the food and the modality of the sensory cue representing it. Such developmental changes are discussed in relation to biological (adiposity rebound) and cognitive (dietary restraint) factors influencing the motivation to eat during middle (6-7years) and late (9-11years) childhood.

Cognitive regulation of food craving: effects of three cognitive reappraisal strategies on neural response to palatable foods

Objective

Obese versus lean individuals show greater reward region and reduced inhibitory region responsivity to food images, which predict future weight gain. Thinking of the costs of eating palatable foods and craving suppression have been found to modulate this neural responsivity, but these cognitive reappraisal studies have primarily involved lean participants. Herein we evaluated the efficacy of a broader range of reappraisal strategies in modulating neural responsivity to palatable food images among individuals who ranged from lean to obese and tested whether Body Mass Index (BMI) moderates the effects of these strategies.

Materials and method

functional Magnetic Resonance Imaging (fMRI) assessed the effects of three cognitive reappraisal strategies in response to palatable food images versus an imagined intake comparison condition in a sample of adolescents (N = 21; M age = 15.2).

Results

Thinking of the long-term costs of eating the food, thinking of the long-term benefits of not eating the food, and attempting to suppress cravings for the food increased activation in inhibitory regions (e.g., superior frontal gyrus, ventrolateral prefrontal cortex) and reduced activation in attention-related regions (e.g., precuneus, and posterior cingulate cortex). The reappraisal strategy focusing on the long-term benefits of not eating the food more effectively increased inhibitory region activity and reduced attention region activity compared to the other two cognitive reappraisal strategies. BMI did not moderate the effects.

Discussion

These novel results imply that cognitive reappraisal strategies, in particular those focusing on the benefits of not eating the food, could potentially increase the ability to inhibit appetitive motivation and reduce unhealthy food intake in overweight individuals.

Impact of insufficient sleep on total daily energy expenditure, food intake, and weight gain

Insufficient sleep is associated with obesity, yet little is known about how repeated nights of insufficient sleep influence energy expenditure and balance. We studied 16 adults in a 14- to 15-d-long inpatient study and quantified effects of 5 d of insufficient sleep, equivalent to a work week, on energy expenditure and energy intake compared with adequate sleep. We found that insufficient sleep increased total daily energy expenditure by ∼5%; however, energy intake--especially at night after dinner--was in excess of energy needed to maintain energy balance. Insufficient sleep led to 0.82 ± 0.47 kg (±SD) weight gain despite changes in hunger and satiety hormones ghrelin and leptin, and peptide YY, which signaled excess energy stores. Insufficient sleep delayed circadian melatonin phase and also led to an earlier circadian phase of wake time. Sex differences showed women, not men, maintained weight during adequate sleep, whereas insufficient sleep reduced dietary restraint and led to weight gain in women. Our findings suggest that increased food intake during insufficient sleep is a physiological adaptation to provide energy needed to sustain additional wakefulness; yet when food is easily accessible, intake surpasses that needed. We also found that transitioning from an insufficient to adequate/recovery sleep schedule decreased energy intake, especially of fats and carbohydrates, and led to -0.03 ± 0.50 kg weight loss. These findings provide evidence that sleep plays a key role in energy metabolism. Importantly, they demonstrate physiological and behavioral mechanisms by which insufficient sleep may contribute to overweight and obesity.

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

BACKGROUND

Flexibility of food reward-related brain signaling (FRS) between food and nonfood stimuli may differ between overweight and normal-weight subjects and depend on a fasted or satiated state.

OBJECTIVE

The objective was to assess this flexibility in response to visual food and nonfood cues.

DESIGN

Twenty normal-weight [mean ± SEM BMI (in kg/m(2)) = 22.7 ± 0.2; mean ± SEM age = 22.4 ± 0.4 y] and 20 overweight (BMI = 28.1 ± 0.3; age = 24.0 ± 0.7 y) participants completed 2 fMRI scans. Subjects arrived in a fasted state and consumed a breakfast consisting of 20% of subject-specific energy requirements between 2 successive scans. A block paradigm and a food > nonfood contrast was used to determine FRS.

RESULTS

An overall stimulus × condition × subject group effect was observed in the anterior cingulate cortex (ACC) (P < 0.006, F((1,38)) = 9.12) and right putamen (P < 0.006, F((1,38)) = 9.27). In all participants, FRS decreased from the fasted to the satiated state in the cingulate (P < 0.005, t((39)) = 3.15) and right prefrontal cortex (PFC) (P < 0.006, t((39)) = 3.00). In the fasted state, they showed FRS in the PFC (P < 0.004, t((39)) = 3.17), left insula (P < 0.009, t((39)) = 2.95), right insula (P < 0.005, t((39)) = 3.12), cingulate cortex (P < 0.004, t((39)) = 3.21), and thalamus (P < 0.006, t((39)) = 2.96). In the satiated state, FRS was limited to the left insula (P < 0.005, t((39)) = 3.21), right insula (P < 0.006, t((39)) = 3.04), and cingulate cortex (P < 0.005, t((39)) = 3.15). Regarding subject group, in the fasted state, FRS in the ACC was more pronounced in overweight than in normal-weight subjects (P < 0.005, F((1,38)) = 9.71), whereas in the satiated state, FRS was less pronounced in overweight than in normal-weight subjects in the ACC (P < 0.006, F((1,38)) = 9.18) and PFC (P < 0.006, F((1,38)) = 8.86), which suggests lower inhibitory control in the overweight.

CONCLUSION

FRS was higher in the overweight in the satiated state; however, when sufficiently satiated, the overweight showed decreased inhibitory control signalling, which facilitates overeating. This trial was registered in the Dutch clinical trial register as NTR2174.

Brain imaging in the context of food perception and eating

PURPOSE OF REVIEW

Eating behavior depends heavily on brain function. In recent years, brain imaging has proved to be a powerful tool to elucidate brain function and brain structure in the context of eating. In this review, we summarize recent findings in the fast growing body of literature in the field and provide an overview of technical aspects as well as the basic brain mechanisms identified with imaging. Furthermore, we highlight findings linking neural processing of eating-related stimuli with obesity.

RECENT FINDINGS

The consumption of food is based on a complex interplay between homeostatic and hedonic mechanisms. Several hormones influence brain activity to regulate food intake and interact with the brain's reward circuitry, which is partly mediated by dopamine signaling. Additionally, it was shown that food stimuli trigger cognitive control mechanisms that incorporate internal goals into food choice. The brain mechanisms observed in this context are strongly influenced by genetic factors, sex and personality traits.

SUMMARY

Overall, a complex picture arises from brain-imaging findings, because a multitude of factors influence human food choice. Although several key mechanisms have been identified, there is no comprehensive model that is able to explain the behavioral observations to date. Especially a careful characterization of patients according to genotypes and phenotypes could help to better understand the current and future findings in neuroimaging studies.

Daytime sleepiness affects prefrontal regulation of food intake

The recent epidemic of obesity corresponds closely with the decline in the average number of hours of sleep obtained nightly. While growing research suggests that sleep loss may affect hormonal and other physiological systems related to food intake, no studies have yet explored the role that sleepiness may play in reducing prefrontal inhibitory control over food intake. Because evidence suggests that women may be more prone to obesity and eating disorders, as well as more likely to suffer from sleep problems, we examined the relation between general daytime sleepiness, brain responses to food stimuli, and self-reported overeating separately for men and women. Thirty-eight healthy adults (16 women; 22 men) aged 18 to 45 underwent functional magnetic resonance imaging (fMRI) while viewing pictures of high- and low-calorie foods. Subjects completed the Epworth Sleepiness Scale (ESS) and provided a rating to the query "how often do you eat more than you intend to." Contrast images comparing brain activation derived from the high- versus low-calorie conditions were correlated voxel-wise with scores from the ESS in a second-level regression model, the output of which was used to predict self-reported overeating. As hypothesized, daytime sleepiness correlated with reduced activation in the ventromedial prefrontal cortex during perception of high- versus low-calorie food images. Moreover, activation within this cluster predicted overeating, but only for women. Findings suggest that normal fluctuations in sleepiness may be sufficient to affect brain regions important for regulating food intake, but that these effects may differ between men and women.

Sex-based fMRI differences in obese humans in response to high vs. low energy food cues

Gender specific effects on human eating have been previously reported. Here we investigated sex-based differences in neural activation via whole-brain blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in response to high energy-dense (high-ED) vs. low-ED visual and auditory food cues in obese men vs. women in both fed and fasted states. The results show that in response to high vs. low ED foods in the fed state, obese men (vs. women) had greater activation in brain areas associated with motor control regions (e.g. supplementary motor areas) whereas women showed greater activation in cognitive-related regions. In the fasted state, obese men had greater activation in a visual-attention region whereas obese women showed greater activation in affective and reward related processing regions (e.g. caudate). Overall the results support our a priori hypothesis that obese women (vs. men) have greater neural activation in regions associated with cognition and emotion-related brain regions. These findings may improve our understanding of sex specific differences among obese individuals in eating behavior.

Preproghrelin gene polymorphisms in obese Japanese women. Minor homozygotes are light eaters, do not prefer protein or fat, and apparently have a poor appetite

Preproghrelin gene single-nucleotide polymorphisms are possible predisposing factors to obesity and other metabolic syndromes. To study the correlation between genotypes and obesity, we recruited 117 obese Japanese women (BMI, 25.0-41.1; average, 31.1). Minor homozygotes for five preproghrelin gene polymorphisms, namely, -1500C>G (rs3755777), -1062G>C (rs26311), -994C>T (rs26312) (promoter region), Leu72Met (rs696217) (exon 2), and +3056T>C (rs2075356) (intron 2), had high values of total and visceral fat areas, waist circumference, and BMI, indicating significant correlation of the polymorphisms with obesity and fat metabolism. Here, we studied the relationship between the genotypes and dietary tendency. Self-administered Diet History Questionnaire showed that total food intake, sugar, and dairy product intake were low in +3056C/C women. Their energy, protein, fat, and meat intake was also low. Energy balance calculation showed considerably reduced fat and protein consumption. Dietary habits were surveyed using Sakata's Questionnaire on Eating Behavior. Of the genotypes, -1062C/C women showed low scores for "motivation for eating" and "eating because of stress or something else." Thus, surprisingly, it was revealed that minor homozygotes for preproghrelin gene polymorphisms were light eaters, did not prefer fat or protein, and apparently had a poor appetite, although they were predisposed to obesity.

Contribution of evening macronutrient intake to total caloric intake and body mass index

The goal of this study was to evaluate the relationship between sleep timing and macronutrient intake as an approach towards better understanding of how sleep and eating affect weight regulation. Fifty-two volunteers (25 women) completed 7 days of wrist actigraphy and food logs. "Average sleepers" (56%) were defined as having a midpoint of sleep <5:30 am and "late sleepers" (44%) were defined as having a midpoint of sleep ≥ 5:30 am. Data were analyzed using t-tests, correlations and regression. Late sleepers consumed a greater amount of protein fat and carbohydrates in the evening (defined as after 8:00 pm) but less fat in the 4 h before sleep. Total protein, protein, carbohydrate, and fat consumed after 8:00 pm, protein consumed within 4h of sleep as well as the percentage of fat consumed after 8:00 were associated with higher BMI. The amount of protein and carbohydrates consumed within 4h of sleep and the amount and percentage of carbohydrate and fat consumed after 8:00 pm were associated with greater total calories. In multivariate analyses controlling for age, gender, sleep timing and duration, protein consumed 4 h before sleep was associated with BMI; carbohydrates consumed after 8 pm, protein and carbohydrates consumed 4h before sleep were associated with higher total calories. Results indicate that evening intake of macronutrients and intake before sleep are not synonymous, particularly among late sleepers. Eating in the evening or before sleep may predispose individuals to weight gain through higher total calories.

Fermentable fibers do not affect satiety or food intake by women who do not practice restrained eating

BACKGROUND

Fiber is thought to enhance satiety, although not all fibers are equally effective. Colonic fermentation may influence satiety and food intake.

OBJECTIVE

To test the satiating properties of four isolated fibers added to chocolate crisp bars.

DESIGN

Within-subject preload design with repeated measures. Each participant completed five conditions, presented in random order.

SUBJECTS

Participants were 22 adult women who do not practice restrained eating (body mass index 18 to 29).

INTERVENTION

The experimental conditions were four fiber treatments: 10 g oligofructose, inulin, soluble corn fiber, or resistant wheat starch in chocolate crisp bars. A no-added-fiber bar was evaluated as the control. The night before each treatment, participants consumed a dinner bar containing 10 g of the same fiber given the next morning.

MAIN OUTCOME MEASURES

Repeated ratings of feelings related to hunger and fullness at the lunch meal were the main measures. Secondary outcomes included breath hydrogen and methane, gastrointestinal symptoms, energy consumed at an ad libitum lunch, and energy from 24-hour dietary recall.

STATISTICAL ANALYSES PERFORMED

Mixed-effect linear models with random intercept for participants to model within-subject correlation.

RESULTS

All treatments were well tolerated. No differences were found in subjective satiety during the morning or food intake at lunch or over 24 hours. The oligofructose bar produced the greatest increase in breath hydrogen, and the most bloating and flatulence symptoms.

CONCLUSIONS

Functional fibers incorporated into chocolate bars at high fiber doses produce greater gastrointestinal symptoms than control, but do not alter satiety, hunger, or food intake compared with control in the short term.

Gender and weight shape brain dynamics during food viewing

Hemodynamic imaging results have associated both gender and body weight to variation in brain responses to food-related information. However, the spatio-temporal brain dynamics of gender-related and weight-wise modulations in food discrimination still remain to be elucidated. We analyzed visual evoked potentials (VEPs) while normal-weighted men (n = 12) and women (n = 12) categorized photographs of energy-dense foods and non-food kitchen utensils. VEP analyses showed that food categorization is influenced by gender as early as 170 ms after image onset. Moreover, the female VEP pattern to food categorization co-varied with participants' body weight. Estimations of the neural generator activity over the time interval of VEP modulations (i.e. by means of a distributed linear inverse solution [LAURA]) revealed alterations in prefrontal and temporo-parietal source activity as a function of image category and participants' gender. However, only neural source activity for female responses during food viewing was negatively correlated with body-mass index (BMI) over the respective time interval. Women showed decreased neural source activity particularly in ventral prefrontal brain regions when viewing food, but not non-food objects, while no such associations were apparent in male responses to food and non-food viewing. Our study thus indicates that gender influences are already apparent during initial stages of food-related object categorization, with small variations in body weight modulating electrophysiological responses especially in women and in brain areas implicated in food reward valuation and intake control. These findings extend recent reports on prefrontal reward and control circuit responsiveness to food cues and the potential role of this reactivity pattern in the susceptibility to weight gain.

Low glycemic load experimental diet more satiating than high glycemic load diet

Effective strategies for reducing food intake are needed to reduce risk of obesity-related cancers. We investigated the effect of low and high glycemic load (GL) diets on satiety and whether satiety varied by body mass index (BMI), gender, and serum leptin. Eighty normal weight (BMI = 18.5-24.9 kg/m²) and overweight/ obese (BMI = 28.0-40.0 kg/m²) adults participated in a randomized, crossover controlled feeding study testing low GL vs. high GL diets. The 28-day diets were isocaloric with identical macronutrient distributions, differing only in GL and fiber. Participants completed visual analog satiety surveys and fasting serum leptin after each 28-day period. T-tests compared mean within- and between-person satiety scores and leptin values. Participants reported 7% greater satiation on the low GL vs. the high GL diet (P = 0.03) and fewer food cravings on the low GL vs. the high GL diet (P < 0.001). Compared to males, females reported less hunger (P = 0.05) and more satiety on the low GL vs. the high GL diet (P < 0.01). Participants with low body fat (<25.0% for men; <32.0% for women) and BMI <25.0 kg/m² reported study food was tastier on the low GL vs. the high GL diet (P = 0.04 and P = 0.05, respectively). In summary, reducing GL, and/or increasing fiber, may be an effective way to lower calories consumed, improve energy balance, and ultimately reduce cancer risk.

Thinking about eating food activates visual cortex with reduced bilateral cerebellar activation in females with anorexia nervosa: an fMRI study

Background

Women with anorexia nervosa (AN) have aberrant cognitions about food and altered activity in prefrontal cortical and somatosensory regions to food images. However, differential effects on the brain when thinking about eating food between healthy women and those with AN is unknown.

Methods

Functional magnetic resonance imaging (fMRI) examined neural activation when 42 women thought about eating the food shown in images: 18 with AN (11 RAN, 7 BPAN) and 24 age-matched controls (HC).

Results

Group contrasts between HC and AN revealed reduced activation in AN in the bilateral cerebellar vermis, and increased activation in the right visual cortex. Preliminary comparisons between AN subtypes and healthy controls suggest differences in cortical and limbic regions.

Conclusions

These preliminary data suggest that thinking about eating food shown in images increases visual and prefrontal cortical neural responses in females with AN, which may underlie cognitive biases towards food stimuli and ruminations about controlling food intake. Future studies are needed to explicitly test how thinking about eating activates restraint cognitions, specifically in those with restricting vs. binge-purging AN subtypes.

fMRI reactivity to high-calorie food pictures predicts short- and long-term outcome in a weight-loss program

Behavioral studies have suggested that food cues have stronger motivating effects in obese than in normal-weight individuals, which may be a risk factor underlying obesity. Previous cross-sectional neuroimaging studies have suggested that this difference is mediated by increased reactivity to food cues in parts of the reward system in obese individuals. To date, however, only a few prospective neuroimaging studies have been conducted to examine whether individual differences in brain activation elicited by food cues can predict differences in weight change. We used functional magnetic resonance imaging (fMRI) to investigate activation in reward-system as well as other brain regions in response to viewing high-calorie food vs. control pictures in 25 obese individuals before and after a 12-week psychosocial weight-loss treatment and at 9-mo follow-up. In those obese individuals who were least successful in losing weight during the treatment, we found greater pre-treatment activation to high-calorie food vs. control pictures in brain regions implicated in reward-system processes, such as the nucleus accumbens, anterior cingulate, and insula. We found similar correlations with weight loss in brain regions implicated by other studies in vision and attention, such as superior occipital cortex, inferior and superior parietal lobule, and prefrontal cortex. Furthermore, less successful weight maintenance at 9-mo follow-up was predicted by greater post-treatment activation in such brain regions as insula, ventral tegmental area, putamen, and fusiform gyrus. In summary, we found that greater activation in brain regions mediating motivational and attentional salience of food cues in obese individuals at the start of a weight-loss program was predictive of less success in the program and that such activation following the program predicted poorer weight control over a 9-mo follow-up period.

Neural substrates underlying interactions between appetite stress and reward

Neurobiological mechanisms that normally control food intake and energy expenditure can be overcome by environmental cues and by stress. Of particular importance is the influence of the mesolimbic reward pathway. In genetically susceptible individuals, problematic over-eating likely reflects a changing balance in the control exerted by homeostatic versus reward circuits that are strongly influenced by environmental factors such as stress. Both stress and activation of the reward pathway have been shown to increase food intake and promote a preference for palatable, high-energy foods. Recent research has focused on the important role of circulating and central neuropeptides that powerfully regulate the brain response to food cues. For example, ghrelin has a potent positive effect on the motivational aspects of food intake, and central oxytocin may be involved in satiety. Thus, the decision to eat, or indeed to over-eat, involves a complex integrated neurobiology that includes brain centres involved in energy balance, reward and stress and their regulation by metabolic and endocrine factors.

The effects of exercise on the neuronal response to food cues

Increased physical activity is associated with successful long-term weight loss maintenance due to mechanisms likely more complex than simply increased energy expenditure. The impact of physical activity on the central regulation of food intake may be an important mechanism of this effect. The objective of this study was to examine the effects of exercise training and acute exercise on the neuronal response to food cues as well as eating behaviors. fMRI was performed in the fasted state at baseline and again after a 6 month progressive exercise intervention (supervised, 5 days/wk) both with and without an acute exercise bout in 12 overweight/obese (5 women, 7 men; BMI 33 ± 4 kg/m(2)) healthy adults. fMRI data were acquired while subjects were presented with visual stimuli of foods of high hedonic value as compared to neutral control objects. Questionnaires on eating behaviors, ratings of appeal and desire for foods, and ratings of appetite (hunger, satiety, prospective intake) using visual analog scales were also performed at baseline and again after the 6-month exercise intervention. While only a trend was observed for a reduction in body weight (102 ± 5 to 99 ± 6 kg, p=0.09), a significant reduction in fat mass was observed (36.4 ± 2.8 to 33.7 ± 3.2 kg, p=0.04), although as expected changes in fat mass were variable (-10.0 to +3.7 kg). Chronic exercise was associated with a reduction in the neuronal response to food, primarily in the posterior attention network and insula. A significant positive correlation between the change in fat/body mass and the change in insula response to food cues with chronic exercise was observed. An acute exercise bout attenuated the effects of chronic exercise. The exercise intervention, however, did not impact any of the measures of appetitive behavior. In summary, despite no effects on behavioral measures of appetite, chronic exercise training was associated with attenuation in the response to visual food cues in brain regions known to be important in food intake regulation. The insula, in particular, appears to play an important role in the potential exercise-induced weight loss and weight loss maintenance.

Altered default network activity in obesity

The regulation of energy intake is a complex process involving the integration of homeostatic signals and both internal and external sensory inputs. To better understand the neurobiology of this process and how it may be dysfunctional in obesity, this study examined activity of the brain's "default network" in reduced-obese (RO) as compared to lean individuals. The default network is a group of functionally connected brain regions thought to play an important role in internally directed cognitive activity and the interplay between external and internal sensory processing. Functional magnetic resonance imaging was performed in 24 lean and 18 RO individuals in the fasted state after 2 days of eucaloric energy intake and after 2 days of 30% overfeeding in a counterbalanced design. Scanning was performed while subjects passively viewed images of food and nonfood objects. Independent component analysis was used to identify the default network component. In the eucaloric state, greater default network activity was observed in RO compared to lean individuals in the lateral inferior parietal and posterior cingulate cortices. Activity was positively correlated with appetite. Overfeeding resulted in increased default network activity in lean but not RO individuals. These findings suggest that the function of the default network, a major contributor to intrinsic neuronal activity, is altered in obesity and/or obese-prone individuals. Future studies of the network's function and its relationship to other brain networks may improve our understanding of the mechanisms and treatment of obesity.

Restraint of appetite and reduced regional brain volumes in anorexia nervosa: a voxel-based morphometric study

BACKGROUND

Previous Magnetic Resonance Imaging (MRI) studies of people with anorexia nervosa (AN) have shown differences in brain structure. This study aimed to provide preliminary extensions of this data by examining how different levels of appetitive restraint impact on brain volume.

METHODS

Voxel based morphometry (VBM), corrected for total intracranial volume, age, BMI, years of education in 14 women with AN (8 RAN and 6 BPAN) and 21 women (HC) was performed. Correlations between brain volume and dietary restraint were done using Statistical Package for the Social Sciences (SPSS).

RESULTS

Increased right dorsolateral prefrontal cortex (DLPFC) and reduced right anterior insular cortex, bilateral parahippocampal gyrus, left fusiform gyrus, left cerebellum and right posterior cingulate volumes in AN compared to HC. RAN compared to BPAN had reduced left orbitofrontal cortex, right anterior insular cortex, bilateral parahippocampal gyrus and left cerebellum. Age negatively correlated with right DLPFC volume in HC but not in AN; dietary restraint and BMI predicted 57% of variance in right DLPFC volume in AN.

CONCLUSIONS

In AN, brain volume differences were found in appetitive, somatosensory and top-down control brain regions. Differences in regional GMV may be linked to levels of appetitive restraint, but whether they are state or trait is unclear. Nevertheless, these discrete brain volume differences provide candidate brain regions for further structural and functional study in people with eating disorders.

Circulating glucose levels modulate neural control of desire for high-calorie foods in humans

Obesity is a worldwide epidemic resulting in part from the ubiquity of high-calorie foods and food images. Whether obese and nonobese individuals regulate their desire to consume high-calorie foods differently is not clear. We set out to investigate the hypothesis that circulating levels of glucose, the primary fuel source for the brain, influence brain regions that regulate the motivation to consume high-calorie foods. Using functional MRI (fMRI) combined with a stepped hyperinsulinemic euglycemic-hypoglycemic clamp and behavioral measures of interest in food, we have shown here that mild hypoglycemia preferentially activates limbic-striatal brain regions in response to food cues to produce a greater desire for high-calorie foods. In contrast, euglycemia preferentially activated the medial prefrontal cortex and resulted in less interest in food stimuli. Indeed, higher circulating glucose levels predicted greater medial prefrontal cortex activation, and this response was absent in obese subjects. These findings demonstrate that circulating glucose modulates neural stimulatory and inhibitory control over food motivation and suggest that this glucose-linked restraining influence is lost in obesity. Strategies that temper postprandial reductions in glucose levels might reduce the risk of overeating, particularly in environments inundated with visual cues of high-calorie foods.

Relation of regional gray and white matter volumes to current BMI and future increases in BMI: a prospective MRI study

OBJECTIVE

This study tested whether global and regional brain volumes correlated with body mass index (BMI) and increases in BMI over 1-year follow-up.

METHODS

A total of 83 young females (M age=18.4, s.d.=2.8; BMI range=17.3-38.9) were scanned using magnetic resonance imaging. Voxel-based morphometry was used to assess global brain volume and regional gray matter (GM) and white matter (WM) volumes in regions implicated in taste, reward and inhibitory control.

RESULTS

Obese participants had less total GM volume than lean and overweight participants. Obese participants had lower total WM volume than overweight participants. BMI correlated with higher WM volumes in the middle temporal gyrus, fusiform gyrus, parahippocampal gyrus, Rolandic operculum and dorsal striatum. Trend-level reduced GM volumes in the superior frontal gyrus and middle frontal gyrus were related to increases in BMI over 1-year follow-up.

CONCLUSION

Findings suggest that BMI is related to global and regional differences in brain matter volume in female adolescents. Most importantly, findings suggest that low GM volume in regions implicated in inhibitory control are related to future weight gain. Results taken in conjunction with prior findings suggest that abnormalities in regional GM volumes, but not WM volumes, increase the risk for future weight gain and abnormalities in regional WM volumes, but not GM volumes, are secondary to weight gain.

Biology's response to dieting: the impetus for weight regain

Dieting is the most common approach to losing weight for the majority of obese and overweight individuals. Restricting intake leads to weight loss in the short term, but, by itself, dieting has a relatively poor success rate for long-term weight reduction. Most obese people eventually regain the weight they have worked so hard to lose. Weight regain has emerged as one of the most significant obstacles for obesity therapeutics, undoubtedly perpetuating the epidemic of excess weight that now affects more than 60% of U.S. adults. In this review, we summarize the evidence of biology's role in the problem of weight regain. Biology's impact is first placed in context with other pressures known to affect body weight. Then, the biological adaptations to an energy-restricted, low-fat diet that are known to occur in the overweight and obese are reviewed, and an integrative picture of energy homeostasis after long-term weight reduction and during weight regain is presented. Finally, a novel model is proposed to explain the persistence of the "energy depletion" signal during the dynamic metabolic state of weight regain, when traditional adiposity signals no longer reflect stored energy in the periphery. The preponderance of evidence would suggest that the biological response to weight loss involves comprehensive, persistent, and redundant adaptations in energy homeostasis and that these adaptations underlie the high recidivism rate in obesity therapeutics. To be successful in the long term, our strategies for preventing weight regain may need to be just as comprehensive, persistent, and redundant, as the biological adaptations they are attempting to counter.

Determinants of appetite ratings: the role of age, gender, BMI, physical activity, smoking habits, and diet/weight concern

Background

Appetite measures are often recorded by visual analogue scales (VAS), and are assumed to reflect central nervous system (CNS) perceptions and sensations. However, little is known about how physiological, psychological, social, and cultural factors influence VAS.

Objective

To investigate whether age, gender, body mass index (BMI), smoking habits, physical activity, diet behaviour, and menstruation cycle are determinants of appetite ratings.

Design

We investigated appetite ratings in different groups of a population during a single meal test, including 178 healthy women (98) and men (80), aged 20–60 years with a BMI of 18.5–35.0 kg/m². Subjects consumed an evening meal composed to meet individual requirements of energy content and recommendations regarding macronutrient composition. Before and every half hour until 3 hours after the meal, subjects filled out VAS for satiety, fullness, hunger, and prospective food intake. They also filled in a questionnaire on eating/slimming behaviour.

Results

Multiple linear regression analyses showed that gender and age were the most powerful predictors of postprandial satiety (p<0.001, adj. R²=0.19) and hunger (p<0.001, adj. R²=0.15). Repeated measures general linear model (GLM) analyses revealed that women felt more satisfied than men (p<0.001) and older subjects felt more satisfied than younger (p<0.01). Furthermore, light/no exercisers felt more satisfied and less hungry than hard/moderate exercisers (p<0.05), but these differences disappeared after adjusting for age and gender. Smokers rated their prospective consumption lower than non-smokers (p<005) and women in the ovulation phase felt less hungry than women in the menstruation phase (p<005). Neither BMI nor diet/weight concern were significantly associated with appetite ratings.

Conclusions

Appetite ratings differed according to age, gender, and physical activity and to a lesser degree for smoking habits and menstruation cycle. Appetite ratings were not influenced by BMI and diet/weight concern. These factors should be considered when planning studies and analysing data concerning appetite sensations.

Neural correlates of the volitional regulation of the desire for food

OBJECTIVE

In this study, we investigate the brain mechanisms of the conscious regulation of the desire for food using functional magnetic resonance imaging. Further, we examine associations between hemodynamic responses and participants' cognitive restraint of eating (CRE), as well as their susceptibility to uncontrolled eating.

SUBJECTS

Seventeen non-vegetarian, right-handed, female Caucasian participants (age: 20-30 years, mean 25.3 years±3.1 s.d.; BMI: 20.2-31.2 kg m(-2), mean 25.1±3.5 s.d.).

MEASUREMENTS

During scanning, our participants viewed pictures of food items they had pre-rated according to tastiness and healthiness. Participants were either allowed to admit to the desire for the food (ADMIT) or they were instructed to downregulate their desire using a cognitive reappraisal strategy, that is, thinking of negative long-term health-related and social consequences (REGULATE).

RESULTS

Comparing the hemodynamic responses of the REGULATE with the ADMIT condition, we observed robust activation in the dorsolateral prefrontal cortex (DLPFC), the pre-supplementary motor area, the inferior frontal gyrus (IFG), the dorsal striatum (DS), the bilateral orbitofrontal cortex (OFC), the anterior insula and the temporo-parietal junction (TPJ). Activation in the DLPFC and the DS strongly correlated with the degree of dietary restraint under both conditions.

CONCLUSION

Cortical activation in the DLPFC, the pre-supplementary motor area and the inferior frontal gyrus (IFG) are known to underpin top-down control, inhibition of learned associations and pre-potent responses. The observed hemodynamic responses in the lateral OFC, the DS, the anterior insula and the TPJ support the notion of reward valuation and integration, interoceptive awareness, and self-reflection as key processes during active regulation of desire for food. In conclusion, an active reappraisal of unhealthy food recruits the brain's valuation system in combination with prefrontal cognitive control areas associated with response inhibition. The correlations between brain responses and CRE suggest that individuals with increased cognitive restraint show an automatic predisposition to regulate the hedonic aspects of food stimuli. This cognitive control might be necessary to counterbalance a lack of homeostatic mechanisms.

Males and females show differential brain activation to taste when hungry and sated in gustatory and reward areas

Although males and females differ in eating behavior and prevalence rates for eating disorders and obesity, little is known about gender differences in cortical activation to pleasant and unpleasant pure tastes during the physiological states of hunger and satiety. Twenty-one healthy young adults (12 females and 9 males) underwent two functional magnetic resonance imaging scans. Using four pure tastants of differing qualities (i.e., salty, sour, bitter, sweet), the present study examined gender differences in fMRI activation during two motivational states (hunger and satiety). There was greater change in fMRI activation from hunger to satiety in males than females in response to all tastes within the middle frontal gyrus (BA 10), insula, and cerebellum. Males also had greater change in activation from hunger to satiety, relative to females, in limbic regions including dorsal striatum, amygdala, parahippocampal gyrus, and posterior and anterior cingulate; however, activation was stimulus dependent, despite equivalent ratings in perceived pleasantness and intensity. Interestingly, males and females showed significant change from hunger to satiety in response to citric acid, suggesting that in addition to gender and physiological condition, stimulus quality is an important factor in taste fMRI activation. These gender differences may have implications for the pathophysiology of eating disorders and obesity.

Obesity-Related Differences between Women and Men in Brain Structure and Goal-Directed Behavior

Gender differences in the regulation of body-weight are well documented. Here, we assessed obesity-related influences of gender on brain structure as well as performance in the Iowa Gambling Task. This task requires evaluation of both immediate rewards and long-term outcomes and thus mirrors the trade-off between immediate reward from eating and the long-term effect of overeating on body-weight. In women, but not in men, we show that the preference for salient immediate rewards in the face of negative long-term consequences is higher in obese than in lean subjects. In addition, we report structural differences in the left dorsal striatum (i.e., putamen) and right dorsolateral prefrontal cortex for women only. Functionally, both regions are known to play complimentary roles in habitual and goal-directed control of behavior in motivational contexts. For women as well as men, gray matter volume correlates positively with measures of obesity in regions coding the value and saliency of food (i.e., nucleus accumbens, orbitofrontal cortex) as well as in the hypothalamus (i.e., the brain's central homeostatic center). These differences between lean and obese subjects in hedonic and homeostatic control systems may reflect a bias in eating behavior toward energy-intake exceeding the actual homeostatic demand. Although we cannot infer from our results the etiology of the observed structural differences, our results resemble neural and behavioral differences well known from other forms of addiction, however, with marked differences between women and men. These findings are important for designing gender-appropriate treatments of obesity and possibly its recognition as a form of addiction.

The insulin-mediated modulation of visually evoked magnetic fields is reduced in obese subjects

Background

Insulin is an anorexigenic hormone that contributes to the termination of food intake in the postprandial state. An alteration in insulin action in the brain, named “cerebral insulin resistance”, is responsible for overeating and the development of obesity.

Methodology/Principal Findings

To analyze the direct effect of insulin on food-related neuronal activity we tested 10 lean and 10 obese subjects. We conducted a magnetencephalography study during a visual working memory task in both the basal state and after applying insulin or placebo spray intranasally to bypass the blood brain barrier. Food and non-food pictures were presented and subjects had to determine whether or not two consecutive pictures belonged to the same category.

Intranasal insulin displayed no effect on blood glucose, insulin or C-peptide concentrations in the periphery; however, it led to an increase in the components of evoked fields related to identification and categorization of pictures (at around 170 ms post stimuli in the visual ventral stream) in lean subjects when food pictures were presented. In contrast, insulin did not modulate food-related brain activity in obese subjects.

Conclusions/Significance

We demonstrated that intranasal insulin increases the cerebral processing of food pictures in lean whereas this was absent in obese subjects. This study further substantiates the presence of a “cerebral insulin resistance” in obese subjects and might be relevant in the pathogenesis of obesity.

Effects of short-chain fructooligosaccharides on satiety responses in healthy men and women

In view of a dramatic increase in the incidence of obesity, the present study examined the appetite effects of a functional fiber as a potential dietary intervention. Fiber may increase satiety. Satiety effects also may be linked to colonic fermentation. Short-chain fructooligosaccharide (scFOS) are fermentable fibers that can be added to foods to influence these actions. The primary objective of this study was to determine if scFOS affects satiety and hunger and has an additive effect on food intake. Using a double-blind crossover design, 20 healthy subjects were assigned to consume two separate doses of 0 g, 5 g, or 8 g of scFOS. The first dose was mixed into a hot cocoa beverage and served with a breakfast meal of a bagel and cream cheese. A beverage was used in the test meal due to the ease with which scFOS can be added to this medium. Satiety was assessed with visual analogue scales (VASs) at 0, 15, 30, 45, 60, 90, 120, 180, and 240 min. Ad libitum food intake was measured at a lunch meal provided at the test site at 240 min. Subjects then recorded their food intake over the remainder of the 24-h study day. The second dose of scFOS was consumed in the form of 3 solid, chocolate-flavored chews (51-67 total kcal) without additional food or drink, 2h prior to the subject's dinner meal. Breath hydrogen measures were collected prior to the breakfast test meal (0 min) and the ad libitum lunch (240 min). Gastrointestinal tolerance was evaluated over the course of the 24-h study day using VAS. All treatments were well tolerated. No differences in subjective satiety over the morning, or food intake at lunch, were found. Over the remainder of the day, the high dose of scFOS reduced food intake in women, but increased food intake in men, suggesting a gender difference in the longer-term response. Breath hydrogen, used as a marker of fermentation, increased in a dose-dependent manner. These results indicate that scFOS undergoes fermentation within 240 min; however, acceptable amounts of scFOS did not enhance acute satiety or hunger.

Neurobiology of food addiction

PURPOSE OF REVIEW

To review recent work on disorders related to food use, including food addiction, and to highlight the similarities and differences between food and drugs of abuse.

RECENT FINDINGS

Recent work on food use disorders has demonstrated that the same neurobiological pathways that are implicated in drug abuse also modulate food consumption, and that the body's regulation of food intake involves a complex set of peripheral and central signaling networks. Moreover, new research indicates that rats can become addicted to certain foods, that men and women may respond differently to external food cues, and that the intrauterine environment may significantly impact a child's subsequent risk of developing obesity, diabetes, and hypercholesterolemia.

SUMMARY

First, work presented in this review strongly supports the notion that food addiction is a real phenomenon. Second, although food and drugs of abuse act on the same central networks, food consumption is also regulated by peripheral signaling systems, which adds to the complexity of understanding how the body regulates eating, and of treating pathological eating habits. Third, neurobiological research reviewed here indicates that traditional pharmacological and behavioral interventions for other substance-use disorders may prove useful in treating obesity.