Facial EMG Activity Is Associated with Hedonic Experiences but Not Nutritional Values While Viewing Food Images

The physiological correlates of hedonic/emotional experiences to visual food stimuli are of theoretical and practical interest. Previous psychophysiological studies have shown that facial electromyography (EMG) signals were related to subjective hedonic ratings in response to food images. However, because other data showed positive correlations between hedonic ratings and objective nutritional values of food, whether the facial EMG reactions to food images could reflect the hedonic evaluation or nutritional assessment of food remains unknown. To address this issue, we measured subjective hedonic ratings (liking, wanting, valence, and arousal) and physiological signals (facial EMG of the corrugator supercilii, zygomatic major, masseter, and suprahyoid muscles, skin potential responses, and heart rates) while participants observed food images that had objective nutritional information (caloric, carbohydrate, fat, and protein contents). The results revealed that zygomatic major EMG activity was positively correlated with ratings of liking, wanting, and valence, but not with any objective nutritional value. These data indicate that facial EMG signals in response to food images reflect subjective hedonic experiences, but not objective nutritional values, associated with the food item.     

Subjective-Physiological Coherence during Food Consumption in Older Adults

Background: Subjective-physiological emotional coherence is thought to be associated with enhanced well-being, and a relationship between subjective-physiological emotional coherence and superior nutritional status has been suggested in older populations. However, no study has examined subjective-physiological emotional coherence among older adults while tasting food. Accordingly, the present study compared subjective-physiological emotional coherence during food consumption among older and younger adults. Methods: Participants consumed bite-sized gel-type foods with different flavors and provided their subjective ratings of the foods while their physiological responses (facial electromyography (EMG) of the corrugator supercilia, masseter, and suprahyoid, and other autonomic nervous system signals) were simultaneously measured. Results: Our primary findings were that (1) the ratings of liking, wanting, and valence were negatively correlated with corrugator EMG activity in older and young adult participants; (2) the positive association between masseter EMG activity and ratings of wanting/valence was weaker in the older than in the young adult group; and (3) arousal ratings were negatively correlated with corrugator EMG activity in the older group only. Conclusions: These results demonstrate commonalities and differences in subjective-physiological emotional coherence during food intake between older and young adults.     

Eating for pleasure or just wanting to eat? Reconsidering sensory hedonic responses as a driver of obesity

Pleasure from foods can stimulate "non-homoeostatic" eating, and might therefore also potentially contribute toward obesity. However, obesity is not reliably associated with heightened hedonic responses to foods. This apparent discrepancy may reflect the differentiation between "liking" and "wanting". Supporting this, behavioural and neurophysiological data on responsiveness to food-related cues indicate that obesity may be associated with increased motivation for food consumption, without necessarily any greater explicit pleasure derived from the orosensory experience of eating. This distinction may have important implications for further research, and applications in commercial and public health approaches to modifying energy intakes.     

The role of implicit wanting in relation to explicit liking and wanting for food: implications for appetite control

Eating is an action open to awareness by the individual; however, it cannot be claimed that processes that control the expression of eating habits are necessarily explicit. This distinction between implicit and explicit processes may enhance understanding of the expression of food reward (particularly the concepts of liking and wanting [Berridge, K. C., & Robinson, T. E. (2003). Parsing reward. Trends in Neurosciences, 26, 507-513] and its importance for human appetite control [Finlayson, G. S., King, N. A., & Blundell, J. E. (2007b). Liking vs. wanting food: Importance for human appetite control and weight regulation. Neuroscience and Biobehavioural Reviews, in press]. The present study investigated the effect of meal-induced satiation on implicit and explicit processes of liking (L) and wanting (W) by developing a computer-based procedure to measure L and W in hungry and satiated states. Explicit measures were derived from analogue ratings whilst an implicit W measure was derived from reaction time in a forced-choice procedure, which also identified food preferences. Seventy subjects (21.8+/-0.9 years, BMI: 22.2+/-0.5 kg/m2) completed the procedure before and immediately following consumption of a savoury test meal. Satiation caused explicit ratings of L and W to decrease in all food categories (p<0.01); but with a more marked decrease for savoury foods compared with sweet foods (p<0.01). Implicit W was increased for sweet categories (p<0.01), but not for savoury. Implicit and explicit measures of L and W independently correlated with preference for sweet foods. This study provides support that implicit and explicit processes of food reward can be simultaneously measured and dissociated using a test meal. Adjustments in hunger were linked to changes in explicit L and W in a manner consistent with sensory specific satiety, while a relationship between hunger and implicit W was absent. We suggest that implicit W is not systematically downregulated by the physiological consequences of food consumption in the same way as hunger and therefore may be largely independent of homoeostatic processes influencing intake.     

Implicit wanting and explicit liking are markers for trait binge eating. A susceptible phenotype for overeating

The present study used a measure of trait binge eating (Binge Eating Scale; BES) to examine its association with behavioural markers of appetite and food reward. Non-obese female participants consumed a preload before freely selecting and consuming from a test meal. Subjective hunger and hedonic measures of explicit liking and implicit wanting for food were obtained. Food selection and intake of the test meal were measured. Findings were compared according to individual differences in trait binge eating. BES scores correlated with BMI, food intake and selection of high fat sweet foods in the test meal. Comparison of BES scores revealed that higher scores were associated with weaker suppression of hunger after the preload, greater explicit liking for food generally, and increased implicit wanting for high fat sweet food. Trait binge eating is functional at low levels and implicit wanting measured simultaneously with explicit liking may be useful markers for reward-driven overconsumption in this susceptible phenotype.     

Changes in hedonic responses to sweet and fat in recently diagnosed non-insulin-dependent diabetic patients during diet therapy.

A study was undertaken to find out how the hedonic responses to, and reported liking and consumption of, sweet and fat foods change during the first months of diet therapy of recently diagnosed patients with non-insulin-dependent diabetes mellitus. The patients were 12 women and 19 men aged 40-65 years. The methods used consisted of hedonic rating tests and summated scales which measured overall tendencies to like and consume fatty and sweet foods. These measurements were made three times at intervals of six weeks. At the same time clinical measurements, weight and glycaemic control were recorded. Hedonic ratings of sweet juices decreased during three months of therapy, but hedonic responses to fatty food items (cheese, milk) remained practically unchanged. After three months of diet therapy the diabetic subjects liked fatty and sweet foods less and consumed them less frequently, which was the aim of the diet therapy. At the same time their metabolic control improved markedly, too.     

Orofacial reactivity to the sight and smell of food stimuli. Evidence for anticipatory liking related to food reward cues in overweight children

Whether food liking may be a risk factor of overconsumption and overweight/obesity remains a controversial issue. So far, most studies used subjective reports to assess consummatory behavior, approaches that might overlook subtle or implicit hedonic changes to sensory properties of foods. Therefore, we used a cue-exposure approach by recording different measures of hedonic processes (orofacial reactivity, self-rated pleasantness, food preference) in 6-11 years old overweight (n=20) and normal-weight (n=20) children. Children were exposed to the smell and sight of high and low-energy density food stimuli and to non-food stimuli during pre- and post-prandial states. Their facial and verbal responses were videotaped and parent's reports of children's eating styles and appetitive traits were collected using the Children's Eating Behavior Questionnaire (CEBQ). Results showed that orofacial reactivity, as an objective measure of anticipatory liking, was more discriminative than self reports, with overweight children displaying more lip sucking than normal-weight children when exposed to high energy food pictures and to food odorants. Orofacial reactivity to food cues was also associated with BMI and children's eating styles (food responsiveness, emotional overeating, and desire to drink). Finally, overweight children classified more frequently non-food odorants as members of the food category during the pre-prandial state than during the post-prandial state, suggesting a possible influence of affective/motivational bias on odor categorization. Our findings suggest that orofacial responsiveness may be relevant to assess the sensitivity to energy-dense food reward cues in overweight children and for signaling, as an index of anticipatory liking, a potential risk for the development of overweight/obesity.     

Influence of substrate oxidation on the reward system, no role of dietary fibre

It has been suggested that a high intake of dietary fibre helps regulate energy intake and satiety. The present study aimed to examine whether dietary fibre influenced the liking and wanting components of the food reward system, the metabolic state or subsequent intake. Five sessions involving 32 normal-weight subjects (16 men and 16 women, 30.6 ± 7.6 year) were held. The sessions differed in the composition of the bread eaten during breakfasts (dietary fibre content varied from 2.4 to 12.8 g/100 g). Several factors such as the palatability, weight, volume, energy content and macronutrient composition of the breakfasts were adjusted. Energy expenditure, the respiratory quotient (R), olfactory liking for four foods, wanting for six other foods, and hunger sensations were evaluated before and after the breakfast, as well as before a morning snack. The results showed no significant differences after ingestion of the various breads. Interestingly, R correlated with olfactory liking and with wanting, which highlights in an original manner the influence of the metabolic state on hedonic sensations for food. In conclusion, dietary fibre was found to have no effect on olfactory liking and wanting, and had no detectable effect on satiety sensations or on subsequent energy intake.     

Food liking, food wanting, and sensory-specific satiety

Sensory-specific satiety refers to a temporary decline in pleasure derived from consuming a certain food in comparison to other unconsumed foods. It has been argued that such a reduction may not be limited to food liking but extends to food wanting as well. Animal research suggests that sensory-specific satiety reflects a reduction in both food liking and food wanting and in the present study it was investigated whether this also holds true for humans. Participants had to consume a certain amount of chocolate milk and afterwards approximately half of the participants played a game to obtain more chocolate milk, whereas the other half played a game to obtain crisps. Participants showed a decline in subjective liking of taste and smell of the chocolate milk in comparison to crisps. Furthermore, they showed less motivation (i.e. wanting) to obtain more chocolate milk. It is concluded that sensory-specific satiety in humans reflects a decrease in both food liking and food wanting.     

Recall of vegetable eating affects future predicted enjoyment and choice of vegetables in British University undergraduate students

Predictions about enjoyment of future experiences are influenced by recalling similar past experiences. However, little is known about the relationship between hedonic memories of past eating episodes and future eating behavior. We investigated recall of previous experiences of eating vegetables and the effect of recall on future predicted liking for and consumption of vegetables. British University undergraduate students were asked to retrieve memories of previous occasions when they ate vegetables and were asked to rate how enjoyable those experiences were (Study 1, n=54). The effect of different types of memory recall (including vegetable eating recall) and visualization of someone else eating vegetables (to control for priming effects) on predicted likelihood of choosing vegetables and predicted enjoyment of eating vegetables was examined (Study 2, n=95). Finally, the effect of recalling vegetable eating memories on actual food choice from a buffet was assessed (Study 3, n=63). It is reported that people recall positive memories of past vegetable consumption (P<0.05) and that reminding people of these experiences results in higher predicted future liking for vegetables (P<0.05) and choice of a larger portion size of vegetables (P<0.05) compared with recall of a personal nonfood memory, a nonvegetable food memory, or visualization of someone else enjoying eating vegetables (increase of approximately 70% in vegetable portion size compared to controls). The results suggest that recall of previous eating experiences could be a potential strategy for altering food choices.     

Gender Differences in Liking and Wanting Sex: Examining the Role of Motivational Context and Implicit Versus Explicit Processing

The present study investigated the specificity of sexual appraisal processes by making a distinction between implicit and explicit appraisals and between the affective (liking) and motivational (wanting) valence of sexual stimuli. These appraisals are assumed to diverge between men and women, depending on the context in which the sexual stimulus is encountered. Using an Implicit Association Test, explicit ratings, and film clips to prime a sexual, romantic or neutral motivational context, we investigated whether liking and wanting of sexual stimuli differed at the implicit and explicit level, differed between men and women, and were differentially sensitive to context manipulations. Results showed that, at the implicit level, women wanted more sex after being primed with romantic mood whereas men showed the least wanting of sex in the romantic condition. At the explicit level, men reported greater liking and wanting of sex than women, independently of context. We also found that women’s (self-reported) sexual behavior was best predicted by the incentive salience of sexual stimuli whereas men’s sexual behavior was more closely related to the hedonic qualities of sexual stimuli. Results were discussed in relation to an emotion-motivational account of sexual functioning.     

Food practices, changes, preferences, and acculturation of Thais in the United States

This study investigated food practices, changes, preferences, and acculturation of Thais in the United States. A questionnaire was mailed to a convenience sample of 182 individuals who were born in Thailand, had lived in the United States for at least 3 months, were age 18 years or older, and had agreed to participate; 102 (56%) completed questionnaires were returned by 62 university students and 40 residents from five states. While living in the United States, the number of meals consumed per day decreased significantly and snacks and food eaten out changed from Thai to American. Of 111 foods listed on the questionnaire, consumption frequency decreased significantly for 29 Thai foods and increased significantly for 33 American foods and total milk food group. Food group mean daily consumption frequencies while living in the United States were 3.5 bread; 3.8 vegetables; 2.2 fruits; 3.6 meat; 1.6 milk; 3.9 fats, oils, and sweets; 2.2 beverages; and 0.9 Thai mixed dishes. Most foods were liked (91 of 111; mean 5.5 or higher on a 9-point hedonic scale). Consumption frequency and liking were significantly positively related for 77 foods. Acculturation (mean 2.6, 1 to 5 scale) was significantly positively related to consumption and liking of some American foods and significantly negatively related to consumption and liking of some Thai foods. This information can be used by dietetics professionals in nutrition education for a Thai population.     

Effects of changes in palatability on food intake and the cumulative food intake curve in man

This study was undertaken to quantify the relationship between palatability ratings and food consumption and to determine whether the initial rate of eating was affected by changes in food palatability without a change in nutrient content. Both men and women were given small samples of foods at a brief exposure taste test and asked to rate how much they liked or disliked them on a 9-point scale (like extremely to dislike extremely). Those who gave at least a 2-point difference in rating between a banana colada frozen yogurt drink with and without adulteration with cumin were given these foods to eat to satiety on non-consecutive days, and the same 9-point scale was used to rate these foods after they had been eaten as meals. Cumin was used as an adulterant because it is not intrinsically unpalatable, but is not liked by many individuals in yogurt-based foods. Intake was approximately 100 g different for every unit of difference on the scale, and higher for liked than disliked food. Intake was significantly different between the adulterated and unadulterated meals. The percentage of variance explained by the difference in palatability was 34% of the total variance but was 67% of the variance within subjects. Correlation between intake and ratings were poor across subjects for both palatability levels (i.e. adulterated and unadulterated). The initial rate of eating was significantly higher under the better liked than under the less liked food. These results indicate that quantification of effects of hedonic ratings on intake within subjects is possible, but that hedonic ratings may not be good discriminators of intake differences between subjects. The initial rate of eating reflects partly on palatability.     

Perception of eating and exercise in children as a function of child and parent weight status

The present study assessed the effects of child body weight (obese/lean) and familial loading for obesity (two obese parents/two lean parents) on the psychophysics of sweetness, fatness and exercise workloads, as well as subjective ratings of foods varying in sugar and fat and activities varying in energy expenditure. Children were measured in a baseline state and at 6 months after the obese children had participated in a family-based behavioral weight control program. No differences between obese and lean children in perceptual ratings were observed. However, offspring of obese or lean parents differed on intensity rating, food palatability and activity enjoyment ratings. Intensity ratings for sweetness in offspring of obese parents was increased, with a similar trend for intensity ratings for fatness. Offspring of obese parents rated all foods and activities with lower palatability and enjoyment ratings than offspring of lean parents. After a 6 month family-based behavioral weight loss treatment, obese children had significant decreases in percent overweight while lean children remained stable. Changes in the pattern of food ratings were observed for the obese children, with a reduction in liking for foods high in fat and/or sugar, and an increase in ratings for food slower in fat and sugar. The effects of parental obesity on food and exercise intensity ratings and hedonic ratings were maintained. Overall, these results suggest parental weight influences behavioral factors related to obesity in children.     

The Three-Factor Eating Questionnaire, body mass index, and responses to sweet and salty fatty foods: a twin study of genetic and environmental associations

BACKGROUND: The relation between body weight and energy-dense foods remains unclear. OBJECTIVE: We estimated the effects of genetic and environmental factors on cognitive and emotional aspects of dieting behavior, body mass index (BMI), and responses to fatty foods and on their relations. DESIGN: A total of 1326 adult twin persons (aged 17-82 y; 17% M and 83% F) from the United Kingdom and Finland completed the revised version of the Three-Factor Eating Questionnaire (TFEQ-R18) and reported the liking and use-frequency of 4 sweet-and-fatty and salty-and-fatty food items (6 items in the United Kingdom and 5 items in Finland). Genetic modeling was done by using linear structural equations. RESULTS: Heritability estimates were calculated separately for the countries and sexes; they were 26-63% for cognitive restraint, 45-69% for uncontrolled eating, and 9-45% for emotional eating, respectively. Of the variation in liking and use-frequency of fatty foods, 24-54% was attributed to interindividual genetic differences. No significant correlations were observed between BMI and fatty food use or liking. However, BMI was positively (mostly genetically) correlated (genetic r = 0.16-0.51) with all of the dieting behaviors, and they correlated with fatty food use and liking ratings. Uncontrolled eating was both genetically and environmentally associated with liking for salty-and-fatty foods (genetic and environmental r = 0.16), and emotional eating was genetically associated with liking for sweet-and-fatty foods (genetic r = 0.31). CONCLUSIONS: The relation between BMI and diet appears to be mediated through dieting behaviors. Dietary counseling should focus on unhealthy dieting behaviors rather than only on direct advice on food use.     

Sweetness, satiation, and satiety

Satiation and satiety are central concepts in the understanding of appetite control and both have to do with the inhibition of eating. Satiation occurs during an eating episode and brings it to an end. Satiety starts after the end of eating and prevents further eating before the return of hunger. Enhancing satiation and satiety derived from foodstuffs was perceived as a means to facilitate weight control. Many studies have examined the various sensory, cognitive, postingestive, and postabsorptive factors that can potentially contribute to the inhibition of eating. In such studies, careful attention to study design is crucial for correct interpretation of the results. Although sweetness is a potent sensory stimulus of intake, sweet-tasting products produce satiation and satiety as a result of their volume as well as their nutrient and energy content. The particular case of energy intake from fluids has generated much research and it is still debated whether energy from fluids is as satiating as energy ingested from solid foods. This review discusses the satiating power of foods and drinks containing nutritive and nonnutritive sweeteners. The brain mechanisms of food reward (in terms of "liking" and "wanting") are also addressed. Finally, we highlight the importance of reward homeostasis, which can help prevent eating in the absence of hunger, for the control of intake.     

Susceptibility to overeating affects the impact of savory or sweet drinks on satiation, reward, and food intake in nonobese women

Taste is involved in food preference and choice, and it is thought that it can modulate appetite and food intake. The present study investigated the effect of savory or sweet taste on satiation, reward, and food intake and according to individual differences in eating behavior traits underlying susceptibility to overeating. In a crossover design, 30 women (BMI = 22.7 ± 2.3; age = 21.9 ± 2.6 y) consumed a fixed energy preload (360 kJ/g) with a savory, sweet, or bland taste before selecting and consuming items from a test meal ad libitum. Sensations of hunger were used to calculate the satiating efficiency of the preloads. A computerized task was used to examine effects on food reward (explicit liking and implicit wanting). The Three Factor Eating Questionnaire was used to compare individual differences in eating behavior traits. Satiation and total food intake did not differ according to preload taste, but there was an effect on explicit liking and food selection. The savory preload reduced liking and intake of high-fat savory foods compared to sweet or bland preloads. The eating behavior trait disinhibition interacted with preload taste to determine test meal intake. Higher scores were associated with increased food intake after the sweet preload compared to the savory preload. Independent of preload taste, disinhibition was associated with lower satiating efficiency of the preloads and enhanced implicit wanting for high-fat sweet food. Savory taste has a stronger modulating effect on food preference than sweet or bland taste and may help to preserve normal appetite regulation in people who are susceptible to overeating.     

The relationship of attitudes and experiences of Finnish youths to their hedonic responses to sweetness in soft drinks

Attitudes to sugar and previous experience (liking and use at present and in childhood) of sweet foods as well as hedonic responses to two levels of sweetness in soft drinks were determined in a young adult population (112 males, 112 females). Females were more negative in their attitudes but they reported greater liking of sweet foods. Sugar attitudes were not related to hedonic responses to normal sweetness (9%) in either sex group, but in the case of lower sweetness (5%) negative attitudes increased along with the rated pleasantness, particularly among males. Reported liking and use of soft drinks had some significant correlations with hedonic responses to both sweetness levels, but experiences of other sweet foods were not related to the hedonic responses to sweetness in soft drinks.     

Motivational state modulates the hedonic value of food images differently in men and women

We investigated visual alimentary alliesthesia in non-fasted (N = 369) and fasted participants (N = 257) viewing photographs of food. Fasted participants were asked to not eat for 12 h before the session. Each participant was shown food and non-food images and rated each image on valence (i.e., pleasantness). The strongest evidence of alliesthesia was found in women. Fasting enhanced the pleasantness of food images for each of the food categories in women, although this alliesthesia effect was smaller in response to dessert foods compared to the less-pleasantly-rated food categories. In addition, non-fasting women exhibited significant positive correlations between hunger ratings and valence ratings of three of the five food categories. There was no significant difference in valence ratings of food between fasting vs. non-fasting men, but non-fasting men showed correlations between hunger and valence that were similar to those observed among the women. No evidence was found of hunger- or fasting-induced enhancement of hedonic ratings of non-foods in women or men, indicating the specificity of the alliesthesia effect for the food images only.