Richard W. Gray

University of Sussex, Brighton, England, United Kingdom

Are you Richard W. Gray?

Claim your profile

Publications (11)39.18 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Manipulations of test meal palatability and nutritional need-state to examine feeding behaviour have, to date, been studied in isolation. Recent investigations have attempted to examine these influences in combination. In the present study, healthy young males received intragastric infusions of soup (265 or 1514 kJ) on four different occasions. The infusion was shortly followed by a meal varying in its palatability (PALATABLE or BLAND). The effect of macronutrient type (CHO or Fat) in the high-energy preloads was also examined in a between-subject manner. High CHO preloads significantly decreased test meal intake and this decrease was unaffected by meal palatability. High fat preloads did not significantly reduce test meal intake. Additionally, more food was consumed following high fat preloads when the test meal was PALATABLE. Within-meal ratings of appetite revealed that hunger was diminished to a greater extent by CHO than by Fat preloads. Appetite was stimulated by the PALATABLE meal to a greater extent in the group receiving Fat than in those receiving the CHO preload. Comparison with a similar oral preloading study revealed differences that suggest possible interactions between cognitive, oro-sensory and gastric controls of feeding when palatable foods are consumed.
    Physiology & Behavior 03/2005; 84(2):193-203. DOI:10.1016/j.physbeh.2004.11.004 · 3.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The role of gastric volume in the short-term control of eating in humans remains unclear, with some studies reporting that food volume alone can reduce appetite but others finding no such effect. A recent study in our laboratory, found effects of preload volume on subjective appetite (hunger, fullness) but not intake, and found effects of preload energy on intake but not appetite. That study used an interval of 30 min between serving preloads and the test meal, and the present study attempted to maximise the effects of the volume manipulation by removing the delay between the preload and test meal. We administered four soup-based preloads varying in volume (150 and 450 ml) using water, and energy density (1.4 and 4.2 kJ/ml) using maltodextrin, producing three energy levels (209, 629, 629 and 1886 kJ; repeated measures). These were followed immediately by an unlimited hot pasta lunch, during which food weight was monitored continuously by computer. Increasing soup volume at constant energy (629 kJ) reduced appetite ratings, but not intake. In contrast, increasing soup energy at constant volume (450 ml) reduced intake, without affecting appetite. The discrepancies between our results and other reported studies suggest that volume is more influential when intakes are large, or that there may be a threshold concentration for nutrients in the GI tract before volume alone is tangibly expressed in subsequent eating.
    Nutritional Neuroscience 03/2003; 6(1):29-37. DOI:10.1080/1028415021000056032 · 2.11 Impact Factor
  • Source
    Martin R Yeomans, Richard W Gray
    [Show abstract] [Hide abstract]
    ABSTRACT: A variety of evidence suggests that endogenous opioid peptides play a role in the short-term control of eating. More recently, opioid receptor antagonists like naltrexone have been approved as a treatment for alcohol dependence. Here we review the evidence for a role of opioid peptides in both normal and abnormal eating and drinking behaviours and in particular try to identify the nature of the role of opioids in these behaviours. Particular attention is paid to the idea that opioid reward processes may be involved both in the short-term control of eating and hedonic aspects of alcohol consumption, and parallels are drawn between the effects of opiate antagonists on food pleasantness and the experience of drinking alcohol. The review also explores the extent to which data from studies using opiate antagonists and agonists provide evidence for a direct role of endogenous opioids in the control of ingestive behaviour, or alternatively whether these data may be better explained through non-specific effects such as the nausea commonly reported following administration of opiate antagonists. The review concludes that the present data suggests a single opioid mechanism is unlikely to explain all aspects of ingestive behaviour, but also concludes that opioid-mediated reward mechanisms play an important control in hedonic aspects of ingestion. The review also highlights the need for further empirical work in order to elucidate further the role of opioid peptides in human ingestive behaviour.
    Neuroscience & Biobehavioral Reviews 11/2002; 26(6):713-28. DOI:10.1016/S0149-7634(02)00041-6 · 10.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Previous research suggests that enhancing the volume of a food preload without altering energy content can result in reduced appetite, although the limited evidence means that the conditions under which this effect will occur are not yet clear. In the present study, we used a Universal Eating Monitor (UEM) to record test meal intake constantly, in parallel with appetite ratings, following soup-based preloads that varied both in volume (150 vs. 450 ml) and energy density (1.4 vs. 4.2 kJ/ml). Healthy young men (n=20) received four different preload conditions (repeated measures) followed by unlimited hot pasta test meals (interval 30 min). They completed appetite ratings during and after each laboratory session, and food diaries for the afternoon and evening following each session. Subjective appetite after the preloads was reduced by the high-volume preloads relative to low-volume preloads, with no difference between the two at each volume level. This indicates an effect of volume, but no effect of energy. Test meal intake in the high-volume, high-energy-density condition was reduced relative to the other conditions, which did not differ from one another. This indicates an effect of total energy, but no effect of volume. The dissociation between these different measures of appetite might be explained in terms of largely cognitive influences on subjective appetite between preload and test meal, contrasted with stronger physiological influences on actual intake during the test meal. With regard to previous studies, it is argued that food volume is more influential under circumstances where gastric volume is closer to its normal limits.
    Physiology & Behavior 06/2002; 76(1):57-64. DOI:10.1016/S0031-9384(02)00675-3 · 3.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of the actual and labelled fat content of a soup preload on appetite at a test meal 30 min later were assessed in 16 healthy men. Each participant ate lunch on four occasions, combining two levels of fat energy (Low, 265 kJ or High, 1510 kJ) and two types of label (Low-fat or High-fat), presented as fictitious soup brand names. Preliminary work established that the Low-fat labels produced an expectation of reduced fat content and lower anticipated hedonic ratings, whereas the High-fat labels generated expectations of a high-fat content and above average hedonic ratings. These expectancies were confirmed in the main experiment, with the soups labelled as high fat rated as both more pleasant and creamy than those labelled low-fat, independent of actual fat content. However, intake at the test meal was unaffected by the preload label, but instead reflected the actual fat (hence, energy) content of the soup, with significantly lower food intake after the high-fat soup regardless of the food label. Rated hunger was lower, and fullness higher, at the start of the meal after the high-fat preloads regardless of how they were labelled, while the pattern of appetite change during the test meal was unaffected by preload. These results suggest that realistic food labels can modify the immediate experience of a consumed food, but do not alter appetite 30 min later in healthy men.
    Physiology & Behavior 08/2001; 73(4):533-40. DOI:10.1016/S0031-9384(01)00502-9 · 3.03 Impact Factor
  • Martin R Yeomans, Richard W Gray, T.H.B. Conyers
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of consumption of a soup preload with added maltodextrin, relative to a no-maltodextrin control soup matched for sensory properties, on intake and the pattern of changes in rated hunger and fullness during lunch were investigated in 24 male volunteers. Preloads were consumed 30 min before lunch and condition-order counterbalanced. Intake at lunch was reduced significantly by 77 g (407 kJ) after the maltodextrin preload, and this reduced intake was associated with a significant reduction in eating rate but not meal duration. Hunger ratings were significantly lower, and fullness ratings significantly higher, at the start of lunch after the maltodextrin compared with control preload. However, the pattern of changes in subjective appetite once eating had started (assessed by analyzing best-fit quadratic functions between rated appetite and actual intake) did not differ between preloads. Neither the rated pleasantness of the lunch food at the start of the test meal nor the pattern of change in pleasantness across the meal differed between preloads. These results imply that the effect of maltodextrin preloads on appetite is to reduce the general desire to eat, and possible mechanisms for this effect are discussed.
    Physiology & Behavior 07/1998; 64(4):501-6. DOI:10.1016/S0031-9384(98)00086-9 · 3.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of the introduction of timed pauses within meals and palatability on food intake and changes in rated appetite during a meal were assessed in three experiments in which volunteers ate a lunch of pasta with a tomato sauce. Eating was monitored using a disguised electronic balance attached to a micro-computer, which also allowed the introduction of timed pauses within meals. In the first experiment, 16 subjects were tested with both a bland and palatable food (with 0.27% oregano), with eating uninterrupted or with pauses after every 50 g consumed during which appetite ratings were completed. Both the addition of oregano and the introduction of regular within-meal pauses enhanced overall intake. Rated hunger increased in the early stages of eating the palatable food in the interrupted condition, and then declined, whereas hunger declined throughout with the bland food. Similarly, the linear function relating intake to time in the uninterrupted condition was greater with the palatable food. In the second experiment, nine subjects ate the palatable food with no pauses within meals, with 30-second pauses with appetite ratings or with 30-second pauses in a non-appetite task. Intake was greater in both pause conditions than when eating was uninterrupted. In Experiment 3, the effect of pause duration was investigated in a further 16 subjects, with either no pause or a pause of 5, 30 or 60 seconds. Subjects ate more in all pause conditions than with no pauses, while ratings of hunger and fullness suggested that subjects were less satisfied at the end of the meal with longer pauses. These data confirm previous work which suggests that palatability exerts its effect by stimulating appetite and eating rate, but also suggest that the introduction of pauses within meals enhances intake as well, contradicting the idea that pausing within meals should reduce intake by allowing more time for post-ingestive satiety to develop.
    Appetite 09/1997; 29(1):61-76. DOI:10.1006/appe.1997.0092 · 2.52 Impact Factor
  • Martin R Yeomans, Richard W Gray
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of 50 mg naltrexone on eating and subjective appetite were assessed in a double-blind placebo-controlled study with 20 male volunteers. Appetite was monitored using a disguised digital balance connected to a micro-computer, which constantly monitored the amount of food remaining, and which automatically interrupted feeding for 30 s after every 50 g consumed to allow appetite ratings to be made. Half the subjects ate pasta with a cheese sauce, and the remainder pasta with a tomato sauce. Subjects ate significantly less of both foods after 50 mg naltrexone than in either the placebo condition or on the initial (familiarisation) day. Naltrexone also reduced the rated pleasantness of both foods, and reduced overall eating rate. When best-fit quadratic functions were used to describe changes in rated hunger in relation to intake within the meal, naltrexone abolished the positive linear component reflecting the initial stimulation of appetite without altering either intercept or the negative quadratic function. Although mood ratings suggested that naltrexone had a mild sedative effect, mood changes alone could not explain the effects of naltrexone on appetite. Overall, these data suggest a specific role for opioids in the stimulation of appetite through palatability.
    Physiology & Behavior 08/1997; 62(1):15-21. DOI:10.1016/S0031-9384(97)00101-7 · 3.03 Impact Factor
  • Martin R. Yeomans, Richard W. Gray
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Physiology & Behavior 09/1996; 60(2):439-46. DOI:10.1016/S0031-9384(96)80017-5 · 3.03 Impact Factor
  • Richard W. Gray, Steven J. Cooper
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of d-fenfluramine on intake and on hedonic responses to taste stimuli in rats were investigated using a modified taste reactivity paradigm. Subjects (n = 15) were first trained to consume a 3% sucrose solution. They were then pretreated with d-fenfluramine (0.3-3.0 mg/kg, i.p.), and tested with access to either 3% sucrose, or a 0.01% quinine HCl solution. In the modified taste reactivity test, chronic oral cannulation was not used; instead, taste reactivity measures were scored during periods of noningestion in a voluntary intake test. d-Fenfluramine reliably reduced both sucrose and quinine consumption, and increased latency to drink at the highest dose. d-Fenfluramine also spared aversive responses to quinine, but reduced positive ingestive responses to sucrose. These results are consistent with an effect of d-fenfluramine to reduce taste palatability, which may, in turn, be an important factor in the effect of this drug on feeding motivation.
    Physiology & Behavior 07/1996; 59(6):1129-35. DOI:10.1016/0031-9384(95)02177-9 · 3.03 Impact Factor
  • Richard W. Gray, Steven J. Cooper
    [Show abstract] [Hide abstract]
    ABSTRACT: The taste reactivity (TR) test was devised as a method to obtain behavioural data in response to gustatory stimuli in neurologically impaired rats, incapable of voluntary feeding. Sapid solutions were infused through surgically implanted intraoral cannulae. Facial and motor responses corresponded well to known hedonic and aversive properties of tastes (e.g., sweet, bitter). TR testing has since proved effective as an adjunct to intake-based methods, in the psychopharmacology of ingestion in the normal rat. We developed a nonsurgical modification of the TR test, in which intact rats sampled stimuli voluntarily. The benzodiazepine receptor agonist midazolam (3.0 mg/kg, IP) was administered to rats first trained to consume a sweet 3% sucrose solution, and later tested with access to a bitter 0.01% quinine solution. Responses were videotaped, and TR measures were scored during periods of noningestion using a frame-by-frame playback. Treatment increased ingestion and facilitated ingestive responses in accordance with published data for cannulated rats. Results support a two-component view of response palatability, in which treatment alters feeding motivation, increasing positive palatability and facilitating ingestion of both palatable and unpalatable stimuli.
    Physiology & Behavior 11/1995; 58(5):853–859. DOI:10.1016/0031-9384(95)00115-Y · 3.03 Impact Factor