Measuring food reward and the transfer effect of sensory specific satiety

Taste and smell function in testicular cancer survivors treated with cisplatin-based chemotherapy in relation to dietary intake, food preference, and body composition

BACKGROUND

Chemotherapy can affect taste and smell function. This may contribute to the high prevalence of overweight and metabolic syndrome in testicular cancer survivors (TCS). Aims of the study were to evaluate taste and smell function and possible consequences for dietary intake, food preference, and body composition in TCS treated with cisplatin-based chemotherapy.

METHODS

Fifty TCS, 1-7 years post-chemotherapy, and 50 age-matched healthy men participated. Taste and smell function were measured using taste strips and 'Sniffin' Sticks', respectively. Dietary intake was investigated using a food frequency questionnaire. Food preference was assessed using food pictures varying in taste (sweet/savoury) and fat or protein content. Dual-Energy X-ray Absorptiometry was performed to measure body composition. Presence of metabolic syndrome and hypogonadism were assessed.

RESULTS

TCS had a lower total taste function, a higher bitter taste threshold, higher Body Mass Index (BMI), and more (abdominal) fat than controls (p < 0.05). No differences in smell function and dietary intake were found. Testosterone level was an important determinant of body composition in TCS (p = 0.016).

CONCLUSION

Although taste function was impaired in TCS, this was not related to a different dietary intake compared to controls. Lower testosterone levels were associated with a higher BMI, fat mass, and abdominal fat distribution in TCS.

Food reward in active compared to inactive men: Roles for gastric emptying and body fat

Habitual exercise could contribute to weight management by altering processes of food reward via the gut-brain axis. We investigated hedonic processes of food reward in active and inactive men and characterised relationships with gastric emptying and body fat. Forty-four men (active: n=22; inactive: n=22, BMI range 21-36kg/m(2); percent fat mass range 9-42%) were studied. Participants were provided with a standardised fixed breakfast and an ad libitum lunch meal 5h later. Explicit liking, implicit wanting and preference among high-fat, low-fat, sweet and savoury food items were assessed immediately post-breakfast (fed state) and again pre-lunch (hungry state) using the Leeds Food Preference Questionnaire. Gastric emptying was assessed by (13)C-octanoic acid breath test. Active individuals exhibited a lower liking for foods overall and a greater implicit wanting for low-fat savoury foods in the fed state, compared to inactive men. Differences in the fed state remained significant after adjusting for percent fat mass. Active men also had a greater increase in liking for savoury foods in the interval between breakfast and lunch. Faster gastric emptying was associated with liking for savoury foods and with an increase in liking for savoury foods in the postprandial interval. In contrast, greater implicit wanting for high-fat foods was associated with slower gastric emptying. These associations were independent of each other, activity status and body fat. In conclusion, active and inactive men differ in processes of food reward. The rate of gastric emptying may play a role in the association between physical activity status and food reward, via the gut-brain axis.

Differing effects of high-fat or high-carbohydrate meals on food hedonics in overweight and obese individuals

Although the effects of dietary fat and carbohydrate on satiety are well documented, little is known about the impact of these macronutrients on food hedonics. We examined the effects of ad libitum and isoenergetic meals varying in fat and carbohydrate on satiety, energy intake and food hedonics. In all, sixty-five overweight and obese individuals (BMI=30·9 (sd 3·8) kg/m2) completed two separate test meal days in a randomised order in which they consumed high-fat/low-carbohydrate (HFLC) or low-fat/high-carbohydrate (LFHC) foods. Satiety was measured using subjective appetite ratings to calculate the satiety quotient. Satiation was assessed by intake at ad libitum meals. Hedonic measures of explicit liking (subjective ratings) and implicit wanting (speed of forced choice) for an array of HFLC and LFHC foods were also tested before and after isoenergetic HFLC and LFHC meals. The satiety quotient was greater after ad libitum and isoenergetic meals during the LFHC condition compared with the HFLC condition (P=0·006 and P=0·001, respectively), whereas ad libitum energy intake was lower in the LFHC condition (P<0·001). Importantly, the LFHC meal also reduced explicit liking (P<0·001) and implicit wanting (P=0·011) for HFLC foods compared with the isoenergetic HFLC meal, which failed to suppress the hedonic appeal of subsequent HFLC foods. Therefore, when coupled with increased satiety and lower energy intake, the greater suppression of hedonic appeal for high-fat food seen with LFHC foods provides a further mechanism for why these foods promote better short-term appetite control than HFLC foods.

The Leeds food preference questionnaire after mild sleep restriction - A small feasibility study

Besides the increased sedentary lifestyle and increased caloric intake, changes in dietary composition may play an important role in the increased prevalence of obesity. Because inadequate sleep could be a risk factor in the aetiology of obesity, reliable methods for assessing food intake and food choice after sleep restriction are needed. We translated the Leeds food preference questionnaire (LFPQ), addressing preferences for sweet/savoury tastes and low-fat/high-fat foods, into Dutch, and tested it in 15 mildly sleep-restricted psychology students. The participants completed the LFPQ in our laboratory on two separate occasions, with approximately one week in between. Sleep on the preceding night was not controlled, but mild sleep-restriction was confirmed by a short sleep latency test (sSLT) or a short maintenance of wakefulness test (sMWT). Each participant completed the sSLT and sMWT once, just before the LFPQ, in a cross-over design randomised for the first test. Differences were present in preferences for food items from different categories (sweet/savoury and low-fat/high-fat; p<0.001). The choice frequencies for various food categories were comparable on both occasions (p=0.27). The choice frequencies for individual items were also comparable on both occasions (p=0.27). The LFPQ is easily implemented under mild sleep-restricted conditions, and translation is straightforward. Future studies using the LFPQ after sleep restriction could elucidate if restricting sleep or longer periods affects food choice, which could underlie increases in obesity risk.

Does low-energy sweetener consumption affect energy intake and body weight? A systematic review, including meta-analyses, of the evidence from human and animal studies

By reducing energy density, low-energy sweeteners (LES) might be expected to reduce energy intake (EI) and body weight (BW). To assess the totality of the evidence testing the null hypothesis that LES exposure (versus sugars or unsweetened alternatives) has no effect on EI or BW, we conducted a systematic review of relevant studies in animals and humans consuming LES with ad libitum access to food energy. In 62 of 90 animal studies exposure to LES did not affect or decreased BW. Of 28 reporting increased BW, 19 compared LES with glucose exposure using a specific ‘learning' paradigm. Twelve prospective cohort studies in humans reported inconsistent associations between LES use and body mass index (−0.002 kg m⁻² per year, 95% confidence interval (CI) −0.009 to 0.005). Meta-analysis of short-term randomized controlled trials (129 comparisons) showed reduced total EI for LES versus sugar-sweetened food or beverage consumption before an ad libitum meal (−94 kcal, 95% CI −122 to −66), with no difference versus water (−2 kcal, 95% CI −30 to 26). This was consistent with EI results from sustained intervention randomized controlled trials (10 comparisons). Meta-analysis of sustained intervention randomized controlled trials (4 weeks to 40 months) showed that consumption of LES versus sugar led to relatively reduced BW (nine comparisons; −1.35 kg, 95% CI –2.28 to −0.42), and a similar relative reduction in BW versus water (three comparisons; −1.24 kg, 95% CI –2.22 to −0.26). Most animal studies did not mimic LES consumption by humans, and reverse causation may influence the results of prospective cohort studies. The preponderance of evidence from all human randomized controlled trials indicates that LES do not increase EI or BW, whether compared with caloric or non-caloric (for example, water) control conditions. Overall, the balance of evidence indicates that use of LES in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water.

How Do Cooks Actually Cook Vegetables? A Field Experiment With Low-Income Households

Vegetables in the diet contribute to disease prevention. However, low-income households underconsume fresh vegetables, perhaps because of cost and of unavailability at nearby stores. A third reason may lurk behind those barriers: cooks’ unfamiliarity with various and appealing ways to prepare vegetables. To illuminate that possibility and to suggest interventions that could be designed more effectively to boost vegetable consumption, this study took the novel step of providing ample, if temporary, supplies of a fresh vegetable to random sets of clients of food pantries. A week later, telephone interviews obtained details about preparations of meals and snacks that household cooks had made with their unexpected bounty. Among the experiment’s 10 vegetables, some were used twice as often as others. Even more striking, cooks practiced a narrow repertoire of preparation methods, dominated by boiling and steaming, across most of the vegetables. Fats and salt were often added to boiled and steamed preparations. Implications are drawn to suggest kinds of recipes—pairings of vegetables and of vegetables with underused means of preparation—that could expand cooks’ repertoires and add variety in flavors, appearances of dishes, meal textures, and aromas.

Functional MRI of Challenging Food Choices: Forced Choice between Equally Liked High- and Low-Calorie Foods in the Absence of Hunger

We are continuously exposed to food and during the day we make many food choices. These choices play an important role in the regulation of food intake and thereby in weight management. Therefore, it is important to obtain more insight into the mechanisms that underlie these choices. While several food choice functional MRI (fMRI) studies have been conducted, the effect of energy content on neural responses during food choice has, to our knowledge, not been investigated before. Our objective was to examine brain responses during food choices between equally liked high- and low-calorie foods in the absence of hunger. During a 10-min fMRI scan 19 normal weight volunteers performed a forced-choice task. Food pairs were matched on individual liking but differed in perceived and actual caloric content (high-low). Food choice compared with non-food choice elicited stronger unilateral activation in the left insula, superior temporal sulcus, posterior cingulate gyrus and (pre)cuneus. This suggests that the food stimuli were more salient despite subject’s low motivation to eat. The right superior temporal sulcus (STS) was the only region that exhibited greater activation for high versus low calorie food choices between foods matched on liking. Together with previous studies, this suggests that STS activation during food evaluation and choice may reflect the food’s biological relevance independent of food preference. This novel finding warrants further research into the effects of hunger state and weight status on STS, which may provide a marker of biological relevance.

Prediction of daily food intake as a function of measurement modality and restriction status

OBJECTIVE

Research on eating relies on various indices (e.g., stable, momentary, neural) to accurately reflect food-related reactivity (e.g., disinhibition) and regulation (e.g., restraint) outside the laboratory. The degree to which they differentially predict real-world consumption remains unclear. Further, the predictive validity of these indices might vary depending on whether an individual is actively restricting intake.

METHODS

We assessed food craving reactivity and regulation in 46 healthy participants (30 women, 18-30 years) using standard measurements in three modalities: a) self-reported (stable) traits using surveys popular in the eating literature, and b) momentary craving ratings and c) neural activation using aggregated functional magnetic resonance imaging data gathered during a food reactivity-and-regulation task. We then used these data to predict variance in real-world consumption of craved energy-dense "target" foods across 2 weeks among normal-weight participants randomly assigned to restrict or monitor target food intake.

RESULTS

The predictive validity of four indices varied significantly by restriction. When participants were not restricting intake, momentary (B = 0.21, standard error [SE] = 0.05) and neural (B = 0.08, SE = 0.04) reactivity positively predicted consumption, and stable (B = -0.22, SE = 0.05) and momentary (B = -0.24, SE = 0.05) regulation negatively predicted consumption. When restricting, stable (B = 0.36, SE = 0.12) and neural (B = 0.51, SE = 0.12) regulation positively predicted consumption.

CONCLUSIONS

Commonly-used indices of regulation and reactivity differentially relate to an ecologically-valid eating measurement, depending on the presence of restriction goals, and thus have strong implications for predicting real-world behaviors.

Understanding and manipulating diet choice in grazing animals

Conventional models of foraging, such as optimal foraging theory, generally take the univariate approach to explain the decisions of consumers on the basis of the intrinsic properties of foods, including nutrient concentration and abundance. However, the food environment is inherently diverse and, as a consequence, foraging decisions are influenced by the interactions among multiple food components and the forager. Foraging behaviour is affected by the consumer’s past experiences with the biochemical context in which a food is ingested, including the kinds and amounts of nutrients and plant secondary compounds in a plant and its neighbours. In addition, past experiences with food have the potential to influence food preference and intake through a mechanism, namely, food hedonics, which is not entirely dependent on the classical homeostatic model of appetite control. Research on the impacts of experience with food context and its behavioural expression in natural settings should pioneer innovative management strategies aimed at modifying food intake and preference of herbivores to enhance their nutrition, health and welfare, as well as the health and integrity of the landscapes they inhabit.

Evaluation of the satiating properties of a nutraceutical product containing Garcinia cambogia and Ascophyllum nodosum extracts in healthy volunteers

A nutraceutical product composed of a combination of Garcinia cambogia, l-carnitine and a seaweed extract of Ascophyllum nodosum has been recently developed. The aim of the present study was to characterize its effects on subjective satiety sensations and food preferences in healthy volunteers. In a crossover design, 28 subjects (21 females and 7 males, aged 31 ± 5, BMI 22.6 ± 1.7) were randomly assigned to receive the active treatment (LIS) or placebo (PL) over one week. At the end of each treatment period, subjects were instructed to consume ad libitum a test meal. Food preferences and appetite sensations were evaluated by means of the Leeds Food Preferences Questionnaire and visual analog scales, before and after meal, over three hours. There were no differences in energy intake between study groups. LIS was associated with a reduction in subjective hunger sensations (p = 0.018) and to an increase in satiety (p = 0.02) and fullness (p = 0.01) ratings. The preference for high fat foods was reduced after consuming the test meal in both study groups. There was a significant effect of LIS treatment on food explicit liking and implicit wanting, as evidenced by an increase in preference for sweet foods (relative to savory foods; p = 0.03 and p = 0.004, respectively), but no differences were observed regarding the preference for low or high fat foods (NS). These results provide proof of principle for the satiating properties of a nutraceutical containing Garcinia cambogia, Ascophyllum nodosum extract and l-carnitine and suggest that it might be useful as an appetite modulator.

Sensory-specific satiation with a pinched nose and eyes closed: testing the sensory modality specificity of satiation

Sensory-specific satiation refers to the decrease in pleasantness derived from a consumed food relative to other unconsumed foods. In the current study, it was investigated to what extent sensory-specific satiation is modality specific. To this end, 80 female participants ate a preferred snack until full while wearing (or not wearing) a blindfold and/or a nose clip. Impaired vision should impede satiation for the appearance of the consumed test snack. Obstructing olfaction should undermine satiation for the smell of the test snack. Indeed, when vision was obstructed, hedonic ratings of specifically snack appearance did not decrease as much. When olfaction was blocked, the hedonic ratings for the flavor of the test snack did not show as much of a reduction. It is concluded that, to a degree, sensory-specific satiation is indeed modality specific.

Examination of food reward and energy intake under laboratory and free-living conditions in a trait binge eating subtype of obesity

Background/Aims: Trait binge eating has been proposed as a “hedonic subtype” of obesity characterized by enhanced food liking and wanting, and a preference for high-fat sweet foods in the laboratory. The current study examined the influence of trait binge eating in overweight or obese women on eating behavior under laboratory and free-living conditions over a 48-h period.

Methods: In a matched pairs design, 24 overweight or obese females (BMI: 30.30 ± 2.60 kg/m²; Age: 25.42 ± 3.65 years) with high or low scores on the Binge Eating Scale (BSE) were divided into one of two groups; Obese Binge (O-B) and Obese Non-binge (O-NB). Energy intake was assessed using combined laboratory energy intake measures and 24-h dietary recall procedures. Liking and wanting were assessed using the Leeds Food Preference Questionnaire (LFPQ).

Results: There was a significant association between overall energy consumed, and energy consumed from snack foods under laboratory and free-living conditions. O-B exhibited a greater preference for sweet snack foods in their laboratory and free-living eating behavior. These findings were supported by greater laboratory-based measures of wanting and craving for this food type in O-B. In addition, O-B consumed significantly more energy than their estimated daily energy requirements in the laboratory suggesting that they over-consumed compared to O-NB.

Conclusions: The measurement concordance between laboratory and free-living based energy intake supports the validity of laboratory-based test meal methodologies Variation in trait binge eating was associated with increased craving and wanting for high-fat sweet foods and overconsumption in the laboratory. These findings support the use of trait binge eating as a common hedonic subtype of obesity and extend the relevance of this subtype to habitual patterns of energy intake.

Questionnaire and laboratory measures of eating behavior. Associations with energy intake and BMI in a community sample of working adults

PURPOSE

The present research compared a self-report measure of usual eating behaviors with two laboratory-based behavioral measures of food reward and food preference.

METHODS

Eating behaviors were measured among 233 working adults. A self-report measure was the Three Factor Eating Questionnaire (TFEQ) Restraint, Disinhibition and Hunger subscales. Laboratory measures were the (RVF) and Explicit Liking (EL) and Implicit Wanting (IW) for high fat food. Outcome measures were body mass index (BMI), and energy intake measured using three 24-h dietary recalls.

RESULTS

Significant bivariate associations were observed between each of the eating behavior measures and energy intake, but only Disinhibition and Hunger were associated with BMI. Multiple regression results showed RVF and EL and IW predicted energy intake independent of the TFEQ scales but did not predict BMI.

CONCLUSION

Laboratory and self-report measures capture unique aspects of individual differences in eating behaviors that are associated with energy intake.

Effect of BMI and binge eating on food reward and energy intake: further evidence for a binge eating subtype of obesity

BACKGROUND

The psychological characteristics of binge eating have been proposed as a phenotype to further understanding of overconsumption and susceptibility to obesity. This study examined the influence of trait binge eating in lean and overweight or obese women on appetite, food reward and energy intake.

METHODS

25 lean and 25 overweight or obese women were categorised as either 'binge type' or 'non-binge type' based on their scores on the Binge Eating Scale. Food reward and food intake were assessed in fasted and fed conditions.

RESULTS

Overweight or obese binge types (O-B) consumed more energy than overweight or obese non-binge types (O-NB) and lean binge (L-B) and non-binge types (L-NB). Both L-B and O-B exhibited greater preference for sweet foods. In O-NB, L-B and L-NB, lower liking and wanting for sweet foods was exhibited in the fed condition compared to the fasted condition. However, in O-B wanting for sweet foods was greater when they were fed compared to when they were in a fasted state.

CONCLUSIONS

These findings provide further support for trait binge eating as a hedonic subtype of obesity. Binge types were characterised by greater intake of high-fat sweet foods and increased wanting for these foods when satiated. Additionally, these findings highlight the potential for separation in liking and wanting for food as a marker of susceptibility to overeat.

Liking compared with wanting for high- and low-calorie foods in anorexia nervosa: aberrant food reward even after weight restoration

BACKGROUND

Recent frameworks for understanding food rewards recognize the role of separable affective and motivational processes (liking and wanting) in driving human eating behavior. Separate assessments of liking and wanting may aid in understanding the complex eating-related behaviors seen in anorexia nervosa (AN).

OBJECTIVE

The aim of this study was to examine separately liking and wanting for foods of different energy densities in women at different stages of AN and in healthy volunteers at both an implicit and an explicit level.

DESIGN

Explicit liking and wanting responses to high- and low-calorie foods were derived from analog ratings, whereas an implicit "wanting" measure was identified by using reaction time in a forced-choice procedure. Explicit and implicit processes were compared across 3 groups of AN participants (current AN, weight-restored AN, and recovered AN) and healthy volunteers.

RESULTS

Currently underweight AN participants explicitly wanted high-calorie foods less than did the other groups. Both current and weight-restored AN groups demonstrated significantly less implicit "wanting" for high-calorie foods and more implicit "wanting" for low-calorie foods-an inverted pattern to never-ill participants.

CONCLUSIONS

The aberrant responses to food that characterize AN may be driven more by altered motivational salience ("wanting") than by explicit liking responses. This pattern of aberrant food reward appears to be independent of weight status. Examining the processes that motivate approach or avoidance of low- and high-calorie foods in AN may aid the development of targeted strategies to augment existing interventions.

Lunch habits of German children and adolescents: composition and dietary quality

BACKGROUND/AIMS

Data from the ongoing, open-cohort Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study were used to describe warm family lunch meals and the association of the lunch composition with total diet quality.

METHODS

2,095 three-day weighed dietary records, collected between 2004 and 2009, from a 4- to 18-year-old DONALD study subgroup were used.

RESULTS

Warm lunch (eating occasions between 11.30 a.m. and 2.29 p.m. including at least one course that is typically consumed warm) was eaten on 68.8% of all record days. Meat lunch (>50%) was predominant, followed by vegetarian (25%), fish (13%) and sweet lunch meals (3%). The prevalence of desserts at lunch was high and beverages were drunk at 80% of lunch meals. A meat lunch was associated with a higher protein (+1.4% energy intake, %E) and fat intake (+1.7%E) than a sweet lunch; also densities of vitamin A, folate and iron were higher. A dessert at lunch decreased protein intake slightly (-0.2%E), but increased carbohydrate (+0.7%E) and added sugar intake (+1.4%E) as well as density of calcium (+18 mg/MJ).

CONCLUSION

Our study proves the impact of lunch on daily dietary quality and yields valuable insights on the development of food and meal-based dietary guidelines.

Long-term consumption of high energy-dense snack foods on sensory-specific satiety and intake

BACKGROUND

The sensory attributes of foods may have an important influence on intake because of sensory-specific satiety (SSS). Foods with high SSS may aid in body weight maintenance as a result of termination of consumption before metabolic satiety. No studies have investigated whether long-term exposure to a food might change SSS or how this affects food intake.

OBJECTIVE

The objective was to compare the effects of daily consumption of 3 energy-dense snack foods (hazelnuts, chocolate, and potato chips) for 12 wk on SSS and ad libitum intake during a tasting session.

DESIGN

One hundred eighteen participants took part in this randomized, controlled, parallel study with 4 arms: control group (no additional food) or ∼1100 kJ/d for each snack. SSS, food intake, and body composition were measured at baseline and at week 12.

RESULTS

Daily consumption of snacks for 12 wk resulted in a statistically significant reduction in SSS in all 3 snack groups (P = 0.015). However, no such changes were seen in the control group (P = 0.608). Ad libitum energy intake increased over the study during the tasting sessions for the snack food across all groups, including the control group (P = 0.039). Inverse associations were found between baseline SSS and BMI (P = 0.039), percentage body fat (P = 0.013), and fat mass (P = 0.004).

CONCLUSION

Habitual consumption of a high energy-dense snack food results in a decrease in SSS, which could lead to a higher energy intake of the snack. This trial was registered at www.anzctr.org.au as ACTRN12609000265279.

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.

Protein status elicits compensatory changes in food intake and food preferences

BACKGROUND

Protein is an indispensable component within the human diet. It is unclear, however, whether behavioral strategies exist to avoid shortages.

OBJECTIVE

The objective was to investigate the effect of a low protein status compared with a high protein status on food intake and food preferences.

DESIGN

We used a randomized crossover design that consisted of a 14-d fully controlled dietary intervention involving 37 subjects [mean ± SD age: 21 ± 2 y; BMI (in kg/m(2)): 21.9 ± 1.5] who consumed individualized, isoenergetic diets that were either low in protein [0.5 g protein · kg body weight (BW)(-1) · d(-1)] or high in protein (2.0 g protein · kg BW(-1) · d(-1)). The diets were followed by an ad libitum phase of 2.5 d, during which a large array of food items was available, and protein and energy intakes were measured.

RESULTS

We showed that in the ad libitum phase protein intake was 13% higher after the low-protein diet than after the high-protein diet (253 ± 70 compared with 225 ± 63 g, P < 0.001), whereas total energy intake was not different. The higher intake of protein was evident throughout the ad libitum phase of 2.5 d. In addition, after the low-protein diet, food preferences for savory high-protein foods were enhanced.

CONCLUSIONS

After a protein deficit, food intake and food preferences show adaptive changes that suggest that compensatory mechanisms are induced to restore adequate protein status. This indicates that there are human behavioral strategies present to avoid protein shortage and that these involve selection of savory high-protein foods. This trial was registered with the Dutch Trial register at http://www.trialregister.nl as NTR2491.

Current progress in the assessment of 'liking' vs. 'wanting' food in human appetite. Comment on '"You say it's liking, i say it's wanting...". On the difficulty of disentangling food reward in man'

Studies that make use of separate measures to capture 'liking' and 'wanting' components of food reward signal a paradigm shift in research on hedonic (over)eating in man. In a recent review, Havermans (2011) highlighted some key methodological and theoretical challenges faced by those working on this issue. Unfortunately, this selective reading of the recent literature in the field presents a skewed picture; but it should not dampen the building momentum. On the other hand the paper is a timely call for researchers to clarify some of the neological confusion that has inevitably been generated along the way. In this response to Havermans (2011), we offer a more robust review of current progress in the assessment of 'liking' vs. 'wanting' food in human appetite. The evidence supports important theoretical and practical implications for a dual-process account of food reward; the developing nature of the research means the majority of these remain tantalisingly unexplored.

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.

The effect of within-meal protein content and taste on subsequent food choice and satiety

It is posed that protein intake is tightly regulated by the human body. The role of sensory qualities in the satiating effects of protein, however, requires further clarification. Our objective was to determine the effect of within-meal protein content and taste on subsequent food choice and satiety. We used a cross-over design whereby sixty healthy, unrestrained subjects (twenty-three males and thirty-seven females) with a mean age of 20·8 (sd 2·1) years and a mean BMI of 21·5 (sd 1·6) kg/m2 were offered one of four isoenergetic preloads (rice meal) for lunch: two low in protein (about 7 % energy derived from protein) and two high in protein (about 25 % energy from protein). Both had a sweet and savoury version. At 30 min after preload consumption, subjects were offered an ad libitum buffet, consisting of food products differing in protein content (low/high) and taste (sweet/savoury). In addition, the computerised Leeds Food Preference Questionnaire (LFPQ) was run to assess several components of food reward. The results showed no effect of protein content of the preloads on subsequent food choice. There was an effect of taste; after eating the savoury preloads, choice and intake of sweet products were higher than of savoury products. No such preference was seen after the sweet preloads. No differences in satiety were observed. To conclude, within one eating episode, within-meal protein content in these quantities seems not to have an effect on subsequent food choice. This appears to be mostly determined by taste, whereby savoury taste exerts the strongest modulating effect. The results of the LFPQ provided insight into underlying processes.

Why liquid energy results in overconsumption

Liquids have been shown to have a low satiating efficiency. The may be related to the high rate of consumption for liquids which may be higher than 200 g/min. In a number of studies, we showed that the positive relationship between eating rate and energy intake is mediated by oro-sensory exposure time. Longer sensory exposure times are consistently associated with lower food intakes. This observation maybe linked to the role of cephalic phase responses to foods. Cephalic phase responses are a set of physiological responses, which are conceived to prepare the digestive system for the incoming flow of nutrients after ingestion, with the aim of maintaining homeostasis. Results from various studies suggest that cephalic phase responses are much smaller (absent) for liquids compared to solids. It is hypothesised that the absence of cephalic phase responses to liquid foods may be one of the causes why liquid energies enter the body undetected and lead to weak energy intake compensation. This idea fits with the concept of the taste system as a nutrient-sensing system that informs the brain and the gastro-intestinal system about what is coming into our body. With liquids, this system is bypassed. Slower eating may help the human body to associate the sensory signals from food with their metabolic consequences. Foods that are eaten quickly may impair this association, and may therefore lead to overconsumption of energy, and ultimately to weight gain.