The Neural Mechanisms Between Successful And Unsuccessful Restrained Eating During Food Choice

The World Health Organization has declared obesity a major problem in global health,with many countries struggling to deal with it and rates of obesity on the rise.The development of obesity is a major risk factor for other chronic diseases,such as type II diabetes,hypertension,hyperlipidemia,cancer,coronary heart disease,gallbladder disease,stroke,and respiratory diseases.A common way of coping with obesity and of controlling one's weight,particularly among women,is dieting.One survey has shown that most women report being very concerned about their weight and having,at some point in their lives,strictly controlled their food intake.Such extreme dieters,who adhere to a deliberate,sustained restriction of caloric intake for long periods of time in order to lose or maintain weight,are referred to as restrained eaters.However,it is very difficult for restrained eaters to maintain or reduce their weight,given the availability of high-calorie foods in most everyday situations;thus,they are often unsuccessful.In an environment full of food temptations,people are constantly making choices about what to eat and how much to eat,and poor food choices and eating behaviors are considered to be the main sources of obesity and failure to control food intake.According to the goal-conflict model of eating,restrained eaters experience a self-control dilemma when faced with the two conflicting goals of eating enjoyment and weight control(eating enjoyment refers to the anticipated pleasure of eating palatable food,while weight control describes the restriction of caloric intake to lose or maintain body weight).The goal-conflict model holds that restrained eaters' failure to restrict their calorie intake is likely to occur when palatable food cues prime eating-enjoymentVI goals and undermine weight-control goals.This thesis used the goal-conflict model to explore the possible success and failure mechanism of restrained eating in food decision–making tasks.In Study 1,we designed a novel food decision–making paradigm to compare the effects of weight-control goals on eating enjoyment in the process of high-calorie food decision making.In Experiment 1,Photoshop software was used to make thin-body pictures and tableware pictures semi-transparent.Under experimental conditions,high-calorie food and semi-transparent thin-body pictures were fused to induce two conflicting goals.For comparison,high-calorie food pictures were combined with semi-transparent tableware pictures.For the control conditions,pictures of high-calorie foods were used.In Experiment 2,diet/weight words were presented on pictures of high-calorie food for the experimental conditions.For comparison,food words were presented on high-calorie food pictures(e.g.,a picture of fried chicken with the words“fried chicken” on it).The control conditions were the same as in Experiment 1,with no stimulus for the high-calorie food pictures.In both experiments,successful restrained eaters(n=33)and unsuccessful restrained eaters(n=34)were asked to indicate whether or not they would eat the food depicted.Experiments 1 and 2 both found that unsuccessful restrained eaters were more likely to choose to eat the high-calorie foods than were successful restrained eaters,and that diet/weight cues reduced high-calorie food choices.The diet/weight cues also caused slower response times than did the comparative and control conditions.The unsuccessful restrained eaters were slower to respond to the diet/weight cues than were the successful restrained eaters.The results also showed that in relation to palatable food cues,the unsuccessful restrained eaters were more regulated by the eating pleasure target and chose more high-calorie foods.The successful restrained eaters,by contrast,were guided more by weight-control goals and were less likely to choose high-calorie foods.Thus,diet/weight cues that activate weight-control goals can reduce unhealthy eating.For the successful individuals,diet/weight cues promoted the association between high-calorie food and weight-control goals,whereas for the unsuccessful individuals,the diet/weight cues led to a conflict between eating pleasure and weight-control goals.Making food decisions between high-calorie and low-calorie foods is seen as a classic self-control dilemma that involves weighing current food enjoyment against future weight and health benefits.Therefore,in Study 2,we adopted a decision-making task involving pairs of high-and low-calorie foods.The task was set up with twoscenarios.When high-and low-calorie foods have the same deliciousness,food decision making is easier,but when high-calorie foods are more delicious than low-calorie foods,food decisions are more difficult,given the need to resist the more tempting high-calorie foods.In Experiment 1,the differences in food decision–making behavior between successful restrained eaters(n=26)and unsuccessful restrained eaters(n=28)were compared.In Experiment 2,the differences in the brain mechanisms of the two groups were explored to validate the goal-conflict model of eating and to identify,if possible,the underlying neural basis for eating-enjoyment and weight-control goals.We verified the results of Study 1 that unsuccessful restrained eaters chose more high-calorie foods than did successful restrained eaters and were more regulated by eating-enjoyment goals.The unsuccessful individuals also exhibited greater activity in the caudate and thalamus,those areas of the brain associated with reward.By contrast,the successful individuals took longer to respond under the difficult decision conditions,chose fewer high-calorie foods than did the unsuccessful individuals,and exhibited stronger functional connectivity between anterior cingulate gyrus–related conflict monitoring and the inferior frontal gyrus and medial frontal gyrus,associated with inhibitory control.This finding provides further support for the goal-conflict model of eating.In an environment of delicious foods,unsuccessful individuals are regulated more by the eating-enjoyment goal,and successful individuals are guided more by the weight-control goal.The eating-enjoyment goal mainly involves the neural reward mechanism,whereas the underlying neural basis of weight-control goals involves the process of conflict monitoring and inhibitory control.Stronger reward responses to food and weaker conflict monitoring and inhibitory control are the main reasons for the failure of restrained eating.In Study 3,we explored the predictions for the effect of conflict-monitoring brain regions and associated reward and inhibitory control neural activity on daily eating behaviors and weight changes occurring over one year.The study was divided into two experiments.In Experiment 5,we used experience sampling to measure the participants' dietary status one week after the food decision task.Two of the participants did not complete the dietary records.The experiment included 26 successful restrained eaters and 26 unsuccessful restrained eaters.The results showed that the greater the activity in the insula and putamen reward/pleasure-related regions and in the hippocampus,which is involved in memory processing,the greater the daily intake of food among unsuccessful individuals.By contrast,among the successful individuals,strongerVIII activity in the anterior cingulate cortex region,which is related to conflict monitoring,reduced their desire enactment.However,the activation levels of the inhibitory control brain regions of the inferior frontal gyrus and middle frontal gyrus did not reduce daily food intake among unsuccessful individuals.For the successful individuals,the stronger activity in the inferior frontal gyrus weakened their food cravings,so that diet management was better.In Experiment 6,the effect of brain activity on weight change in the course of a year was investigated.Two participants failed to report data;finally,25 successful restrained eaters and 27 unsuccessful restrained eaters were included.Activity in the insula,putamen,amygdala,and hippocampus predicted weight changes over one year among the unsuccessful individuals.No brain regions were found to predict weight changes over the course of one year for the successful individuals.In conclusion,this study illustrated the potential neural basis of the influence of eating-enjoyment goals on eating and weight: external food-reward cues drive the striatum's reward system function;the insula system involved in the translation of homeostatic and interoceptive signals into self-awareness and what may be subjectively experienced as a feeling caused by excessive eating,and the pleasant emotions from the enjoyment of eating food encoded in the memory,which strengthens reward seeking and the taste perception of food,lead to repeated excessive eating and consequent weight gain.In Study 4,we attempted to find ways to reduce unhealthy eating in daily life.Food labels are a national health intervention policy to remind consumers of the nutritional value of food products.Previous evidence has shown that labels that are color coded in a manner inspired by traffic lights are more effective in conveying nutritional levels and increasing the selection of healthier products than purely numeric daily-amount guideline labels are.We aimed to explore the effectiveness of traffic-light and daily-amount guideline labels at the behavioral level(Experiment 7)and neural level(Experiment 8)for food decision–making tasks.Forty-four female restrained eaters were recruited to participate in a food choice task that involved indicating whether or not they would want to eat various food items of different calorific values,presented with either a color-coded traffic-light label or a numeric daily-amount guideline label.We found that a clear,red traffic-light label had the potential to reduce high-calorie food selections,activating the superior medial frontal gyrus and the supplementary motor area,which are implicated in the execution of responses and motor inhibition.For the same stimulus contrast,we also found increased activation in the anterior cingulatecortex,which is associated with salient information monitoring.Moreover,we found stronger functional connectivity between the anterior cingulate cortex and inhibitory regions(inferior and middle frontal gyri)for the red traffic-light labels than for the daily-amount guideline labels.These results suggest that traffic-light-inspired labels are a more effective public-policy intervention than numeric labels conveying daily-amount guidelines.This study was the first used f MRI technology to explore the brain mechanisms that lead to the failure and success of restrained eating during food decision-making tasks.Theoretically,it provides empirical support for the goal-conflict model of eating from the new perspective of internal and external conflict,and expand the model from the neural level to reveal the potential neural basis of eating enjoyment and weight control goals.In terms of research methods,a novel conflict food decision task was designed,and the effects of eating enjoyment and weight control goals were discussed.In terms of research contents,the two sub-components of self-control were further studied,conflict monitoring and inhibition control were discussed,the patterns of activation and functional connection of brain regions related to conflict monitoring and inhibition control were compared between the successful and the unsuccessful restrained eaters.Finally,we observed the dietary index and body weight change index of the subjects' daily life,and explored the influence of brain activation level on diet and body weight,which made the results more ecological validity and practical significance.In summary,we further validated the goal-conflict model of eating and extended the model at the neural level,revealing the underlying neural processes of eating-enjoyment and weight-control goals in guiding eating behaviors and clarifying the reasons for the success or failure of restrained eating.Our research also provides a feasible scheme for clinical application.In future interventions,measures can be taken to target reward and self-control mechanisms(conflict monitoring and inhibition control),for example,by using transcranial direct-current stimulation to stimulate the relevant brain areas to improve eating behavior.In addition,traffic-light nutrition labels can be used to reduce the purchase of unhealthy food products.