Selective effects of naltrexone on food pleasantness and intake

The effects of 50 mg naltrexone on both pleasantness and intake of 10 common food items were investigated using a double-blind placebo-controlled study with 16 male volunteers. Rated food pleasantness was reduced significantly in the naltrexone condition compared with both controls (placebo and baseline). However, pleasantness ratings were not affected uniformly across foods, with sweetened, fatty, and high-protein foods being most affected. Changes in rated unpleasantness generally mirrored those for pleasantness, but evaluations of saltiness and sweetness were unaffected by naltrexone. Although total intake was reduced in the naltrexone condition, this was not significant compared with placebo. However, fat and protein intakes were significantly less following naltrexone. The effect of naltrexone on intake was also food dependent, but in this case intake of sweet foods was spared relative to other food categories. The apparent discrepancy between liking and intake data with sweet foods could be interpreted in terms of the likely influence of normal eating styles on food selection during a buffet-style meal, and may explain some contradictions in previous studies of this kind. The implications for understanding opioid involvement in food acceptability are discussed.     

Acquired aversions as the basis for varied diets of ruminants foraging on rangelands

Ruminants eat an array of plant species that vary in nutrients and toxins. This selection makes intuitive sense, but no theories adequately explain this diversity. Some maintain it reduces the likelihood of overingesting toxins, whereas others contend it meets nutritional needs. Nevertheless, herbivores seek variety even when toxins are not a concern and nutritional needs are met. I offer another explanation for this behavior, one which encompasses the avoidance of toxins and the acquisition of nutrients. A key concept in this theory is aversion, the decrease in preference for food just eaten as a result of sensory input (a food's taste, odor, texture, i.e., its flavor) and postingestive effects (effects of nutrients and toxins on chemo-, osmo-, and mechano-receptors) unique to each food. Aversions are pronounced when foods contain toxins or high levels of rapidly digestible nutrients; they also occur when foods are deficient in specific nutrients. Aversions occur even when animals eat nutritionally adequate foods because satiety (satisfied to the full) and surfeit (filled to nauseating excess) represent points along a continuum, and there is a fine line between satiety and aversion. Thus, eating any food is likely to cause a mild aversion, and eating a food too frequently or in excess is likely to cause a strong aversion. Aversions are involuntary and are not the result of conscious decisions by an animal. Aversions yield benefits (e.g., obtain a balanced diet, reduce ingestion of toxic foods, optimize foraging and rumination times, sample foods, maintain a diverse microflora in the rumen) that are often mistaken as the cause of varied diets. In this article, I discuss the subtle ways in which aversions diminish preference and cause animals to eat a variety of foods.     

Bulimia and taste: Possible interactions.

Potential abnormalities of taste were examined in bulimic subjects who purged by vomiting and in controls. When spatial testing of the tongue and palate was performed by direct local application of sweet, salty, sour, and bitter solutions, bulimics showed a selective spatial loss on the palate. The palate may be affected by purging because vomit is directed toward the roof of the mouth where the palate receptors are located. The data suggest that the acid in vomit damages these receptors. Bulimics and controls did not differ in their basal ratings of intensity or pleasantness of sweet, salty, sour, and bitter stimuli when these were sipped rather than directly applied to the tongue. However, after ingesting a glucose load, controls found sweet taste significantly less pleasant, whereas bulimics did not. The results suggest that bulimics may also have an abnormal experience of satiety. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hedonic and sensory characteristics of odors conditioned by pairing with tastants in humans.

Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses to the sensory properties of fat of neurons in the primate orbitofrontal cortex

The primate orbitofrontal cortex is a site of convergence of information from primary taste, olfactory, and somatosensory cortical areas. We describe the responses of a population of single neurons in the orbitofrontal cortex that responds to fat in the mouth. The neurons respond, when fatty foods are being eaten, to pure fat such as glyceryl trioleate and also to substances with a similar texture but different chemical composition such as paraffin oil (hydrocarbon) and silicone oil [Si(CH3)2O)n]. This is evidence that the neurons respond to the oral texture of fat, sensed by the somatosensory system. Some of the population of neurons respond unimodally to the texture of fat. Other single neurons show convergence of taste inputs, and others of olfactory inputs, onto single neurons that respond to fat. For example, neurons were found that responded to the mouth feel of fat and the taste of monosodium glutamate (both found in milk), or to the mouth feel of fat and to odor. Feeding to satiety reduces the responses of these neurons to the fatty food eaten, but the neurons still respond to some other foods that have not been fed to satiety. Thus sensory-specific satiety for fat is represented in the responses of single neurons in the primate orbitofrontal cortex. Fat is an important constituent of food that affects its palatability and nutritional effects. The findings described provide evidence that the reward value (or pleasantness) of the mouth feel of fat is represented in the primate orbitofrontal cortex and that the representation is relevant to appetite.     

Effects of smoking cessation, restrained eating, and motivational states on food intake in the laboratory.

20 smokers, 20 abstaining smokers (for 24 hrs), and 20 nonsmokers completed ratings of motivational state before and after a taste test, to examine the mediating effects of motivations to eat and smoke, cross-motivational satiating effects, and restrained eating on post-smoking-cessation food intake in the laboratory. The results suggest that the abstaining smokers consumed more carbohydrates, calories, fat, protein, and mass than the smokers; that food intake was related to the urge to eat, the urge to smoke, and craving for a cigarette; and that eating could reduce the desire to smoke. However, these effects were only apparent for the female smokers. In addition, restrained eating predicted increases in postcessation food intake. The results are discussed in terms of a substitution theory of motivational states. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A role for sweet taste: Calorie predictive relations in energy regulation by rats.

Animals may use sweet taste to predict the caloric contents of food. Eating sweet noncaloric substances may degrade this predictive relationship, leading to positive energy balance through increased food intake and/or diminished energy expenditure. These experiments were designed to test the hypothesis that experiences that reduce the validity of sweet taste as a predictor of the caloric or nutritive consequences of eating may contribute to deficits in the regulation of energy by reducing the ability of sweet-tasting foods that contain calories to evoke physiological responses that underlie tight regulation. Adult male Sprague-Dawley rats were given differential experience with a sweet taste that either predicted increased caloric content (glucose) or did not predict increased calories (saccharin). We found that reducing the correlation between sweet taste and the caloric content of foods using artificial sweeteners in rats resulted in increased caloric intake, increased body weight, and increased adiposity, as well as diminished caloric compensation and blunted thermic responses to sweet-tasting diets. These results suggest that consumption of products containing artificial sweeteners may lead to increased body weight and obesity by interfering with fundamental homeostatic, physiological processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sweet tooth demonstrated: Individual differences in preference for both sweet foods and foods highly sweetened.

A total of 9 women and 9 men, aged 19–40 years, rated the sweetness of samples of chocolate, lime drink, and tomato soup relative to their personally ideal levels of sweetness for each food, with the conditions of each test session designed to eliminate various sources of bias. The method yielded precise estimates of the individual's most preferred concentration of sugar and of his or her tolerance of deviations from ideal. This linear precision allowed assessment of the degree to which the ideal food sugar level was a personal characteristic. We found that individuals differed significantly in peak-preferred levels of sugar, both generally across foods and with some variation relatively among foods. Also, the peak sweetness preferences for the three foods correlated significantly with several rated choices of sweet foods over nonsweet foods. This is evidence for the full construct of a sweet tooth—both a strong liking for sweet foods and a liking for strongly sweetened foods. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of gender and taste class in the effects of stress on eating.

In a study of the effects of stress on eating, healthy nonsmoking Ss (26 men and 28 women, aged 17–41 yrs) were shown a film about industrial accidents (stress condition) or a pleasant travelog (control condition) and had access to sweet, salty, and bland snack food. Stress markedly and significantly decreased food consumption by men but resulted in some increased food consumption by women. Across the 3 taste categories, men consistently ate less under stress than in the control condition. In contrast, women ate nearly twice as much sweet food and more bland food under stress than in the control condition, but these effects were not statistically significant. Thus, the relationship between stress and eating depends on the sex of the S and may relate to type of food available. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Color as a factor in food choice

From birth, nature teaches us to make judgements on our environment based in large measure on color. As such, it plays a key role in food choice by influencing taste thresholds, sweetness perception, food preference, pleasantness, and acceptability. Its role is elusive and difficult to quantify, however, which at times has placed color in a secondary role to the other sensory characteristics, a position not entirely consistent with the facts. Color, in a quantitative sense, has been shown to be able to replace sugar and still maintain sweetness perception in flavored foods. It interferes with judgments of flavor intensity and identification and in so doing has been shown to dramatically influence the pleasantness and acceptability of foods. Studies in the literature have used cross-sectional population panels to study these effects, but a recent investigation of color-sensory interactions in beverages has compared the response of a college age group with the response of a panel consisting of a more mature population. Interestingly, the older group showed significant differences from the college age group in their response to the effects of color on several sensory parameters as well as showing a direct correlation between beverage consumption and color. Color is often taken for granted, but this position must be reevaluated in view of such studies and the need to create more appealing foods for different segments of our society.     

Improved large-scale isolation of breeder porcine islets: possibility of harvesting from nonheart-beating donor

Previous studies of the effect of carbonation on taste perception have suggested that it may be negligible, manifesting primarily in increases in the perceived intensity of weak salt and sour stimuli. Assuming CO2 solutions in the mouth stimulate only trigeminal nerve endings, this result is not altogether surprising; however, there are neurophysiological data indicating that CO2 stimulates gustatory as well as trigeminal fibers. In that case, carbonation might alter the quality profile of a stimulus without producing substantial changes in overall taste intensity--much as occurs when qualitatively different taste stimuli are mixed. To address this possibility, subjects were asked to rate the total taste intensity of moderate concentrations of stimuli representing each of the basic tastes and their binary combinations, with an without added carbonation. They then subdivided total taste intensity into the proportions of sweetness, saltiness, sourness, bitterness and 'other taste qualities' they perceived. The addition of carbonation produced only small increases in ratings of total taste intensity. However, rather dramatic alterations in the quality profiles of stimuli were observed, particularly for sweet and salty tastes. The nature of the interaction is consistent with a direct effect of carbonation/CO2 on the gustatory system, although the possibility that at least some of the observed effects reflect trigeminal-gustatory interactions cannot be ruled out.     

The reaction of S-nitrosoglutathione with superoxide

The gut peptide glucagon-like peptide 1(7-36) amide (GLP-1) is released into the circulation after food intake. GLP-1 has been shown to have an incretin effect and inhibits gastrointestinal motility in humans. In rats, intracerebral administration of GLP-1 results in reduced food intake. Obese humans have been found to have an attenuated plasma GLP-1 response to a mixed meal. To approximate the physiologic state, GLP-1 or saline was administered intravenously and randomly at the beginning of a test meal served on a universal eating monitor to 6 obese subjects to test our hypothesis that GLP-1 influences termination of food intake (and thus food intake during a meal) and feelings of satiety in humans. As a marker for gastric emptying, 1.5 g acetaminophen was given at the start of the meal. Blood samples for analysis of acetaminophen, insulin, glucose, glucagon, and C-peptide were obtained. Hunger, fullness, and food choice were assessed with visual analogue scales and food-choice questionnaires. GLP-1 infusion resulted in a prolonged period of reduced feelings of hunger, desire to eat, and prospective consumption after the meal. The rate of gastric emptying was slower during infusion of GLP-1. Postprandial blood glucose concentrations were reduced during the GLP-1 infusion, but the amount of energy consumed, eating rate, and plasma concentrations of insulin, glucagon, and C-peptide were unchanged. GLP-1 given exogenously at the start of a meal did not seem to affect meal termination or the amount of food eaten. However, postprandial feelings of hunger decreased, suggesting that exogenous GLP-1 may influence feelings of hunger and satiety in humans.     

Class differences in the food rules mothers impose on their children: a cross-national study

Many studies indicate that children in middle-class families have healthier eating habits than children in lower class families. Class differences in food rules, which parents and especially mothers impose on their children, may underlie these social inequalities in food consumption. The present study uses education as a classifying variable and analyses whether mothers with higher education prescribe more "healthy" foodstuffs for their children and whether they restrict more "unhealthy" food items than less educated mothers. Moreover, the study examines whether higher class mothers consider health aspects more often and the preferences of their family members less often in their choice of food, and whether class differences in these considerations explain class differences in food rules. To answer these questions, questionnaires on the food practices of 849 women living in middle-class or lower class districts in Maastricht (the Netherlands), Liège (Belgium) and Aachen (Germany) were collected and analysed. The majority of mothers in each city prescribed primarily foods that were served at dinner like meat and vegetables, and most mothers limited their children's consumption of sweet foods, soft drinks and snacks. Higher class mothers restricted more foods, but prescribed as many food items as their lower class counterparts. Class differences in the number of restricted foods were partly, but not completely, explained by class differences in health and taste considerations. Despite national variations in dietary habits and possibly in the education of children, class differences in food rules and the explanatory power of health and taste considerations were comparable in the three cities.     

The effect of dietary fiber supplementation in man. I. Modification of eating habits

Six subjects were studied for an 8-week period that consisted of a 3-week control period, followed by a 3-week period during which their daily diets were supplemented with 3 oz of a high fiber breakfast food, All-bran, and a final 2 weeks on their regular diet. Daily diet records of food intake were recorded and analyzed for seven dietary constituents; carbohydrates, proteins, fats, cholesterol, fiber, alcohol, and total calories. The most significant change in eating behavior due to the fiber food supplementation was a decrease in eating eggs, butter, and breakfast meats. These foods were most often replaced because all six subjects chose to eat the major portion of All-bran during breakfast. An increase in milk and fruit also occurred during the supplemented feeding. These particular foods were added to make All-bran more palatable and served to increase carbohydrate and protein intake. Five subjects added the supplement to the between meal-time intake and thus caused an increase in total daily caloric intake. At lunch and dinner few foods were altered with no particular pattern of substitution. Notwithstanding the knowledge that increased fiber content may have beneficial effects, none of the subjects modified his eating behavior to include even 1 oz of a high fiber food daily after the experimental period was concluded. Thus behavior modification by forced diet intake of a high fiber breakfast food resulted in definite diet pattern changes that did not persist following the experimental period.     

Effects of the Presence of Others on Food Intake: A Normative Interpretation.

The authors review the effect of the presence of others on food intake. In social facilitation studies, people tend to eat more in groups than when alone. In modeling studies, the presence of others may facilitate or inhibit intake, depending on how much these other people eat. Studies of impression management demonstrate that people tend to eat less in the presence of others than when alone. The authors attempt to reconcile these divergent literatures by reference to a model of inhibitory norms that govern eating. In the presence of palatable food, and in the absence of clear signals of satiety, people look outward to cues from the environment to determine when to stop eating. Socially derived inhibitory norms can account for either increased or decreased intake in the presence of others, depending on how much the others eat and the extent to which one is eager to impress them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessing yourself as an emotional eater: Mission impossible?

Objective: The extent to which individuals are emotional eaters has typically been assessed by people’s self-reported desire to eat when they experience negative emotions. Elevated scores on these emotional eater scales have been associated with eating pathology and obesity. However, evidence that individuals scoring high on these scales truly increase their food intake during emotional encounters is inconclusive. The current studies tested whether emotional eater scales capture the proposed tendency to eat when feeling emotional. Design: In four experiments with different emotion induction procedures, female participants were randomly assigned to negative emotion or control conditions. In the control conditions positive or no emotions were induced. Next, food consumption was assessed by bogus taste tests. Main Outcome Measures: Emotional eater status, emotional experience, and actual consumption of different food types. Results: Individuals describing themselves as emotional eaters did not increase food intake during emotional encounters as compared to control conditions or individuals not judging themselves as emotional eaters. Conclusion: The results suggest that self-reported emotional eaters do not increase food intake during emotional encounters in the laboratory. Implications of these findings are discussed, including the idea that it may be complex to adequately assess one’s own emotional eating behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lack of Interference in Long-Term Memory for Socially Learned Food Preferences in Rats (Rattus norvegicus).

Outside the laboratory, rats (Rattus norvegicus) are likely both to interact with several conspecifics that have eaten various foods and to eat a variety of foods themselves before they encounter any particular food for which they have a socially enhanced preference. Here the authors examine the stability of rats' socially learned food preferences following 6 days of potentially disruptive ingestive experiences. The authors found that 6 days of (a) eating unfamiliar foods, (b) interacting with demonstrators that had eaten unfamiliar foods, or (c) both eating unfamiliar foods and interacting with demonstrators that had eaten those foods had no measurable effect on rats' socially learned food preferences. The stability of socially enhanced food preferences over time and despite potentially disruptive experiences is consistent with the view that social learning about foods is an important determinant of the food choices of free-living Norway rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absence of satiety during sham feeding in the rat.

In 2 experiments, a total of 9 Sprague-Dawley rats with chronic gastric fistulas were trained to eat a liquid diet. Results indicate that when the fistulas were opened for the first time, Ss sham-fed eagerly and did not become satiated during test periods of 2 or 7.5 hrs. This sustained hyperphagia occurred after long (17 hrs) or short (10-30 min) intermeal intervals. The experience of sustained hyperphagia when gastric fistulas were open did not affect intake of the same diet on the next day when gastric fistulas were closed. When taste and other oropharyngeal stimuli acted alone during sham feeding, they did not elicit satiety. It is concluded that the occurrence of satiety in rats is critically dependent on an inhibitory reflex elicited by ingested food accumulating in the stomach and moving through the small intestine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of sensory perception of foods on appetite and food intake: a review of studies on humans

OBJECTIVE: How much do the sensory properties of food influence the way people select their food and how much they eat? The objective of this paper is to review results from studies investigating the link between the sensory perception of food and human appetite regulation. CONTENT OF THE REVIEW: The influence of palatability on appetite and food intake in humans has been investigated in several studies. All reviewed studies have shown increased intake as palatability increased, whereas assessments of the effect of palatability using measures of subjective appetite sensations have shown diverging results, for example, subjects either feel more hungry and less full after a palatable meal compared to a less palatable meal, or they feel the opposite, or there is no difference. Whether palatability has an effect on appetite in the period following consumption of a test meal is unclear. Several studies have investigated which sensory properties of food are involved in sensory-specific satiety. Taste, smell, texture and appearance-specific satieties have been identified, whereas studies on the role of macronutrients and the energy content of the food in sensory-specific satiety have given equivocal results. Different studies have shown that macronutrients and energy content play a role in sensory-specific satiety or that macronutrients and energy content are not a factor in sensory-specific satiety. Sensory-specific satiety may have an important influence on the amount of food eaten. Studies have shown that increasing the food variety can increase food and energy intake and in the short to medium term alter energy balance. Further knowledge about the importance of flavour in appetite regulation is needed, for example, which flavour combinations improve satiety most, the possible connection between flavour intensity and satiety, the effect of persistence of chemesthetic sensation on palatability and satiety, and to what extent genetic variation in taste sensitivity and perception influences dietary habits and weight control.