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OBJECTIVES:The present study evaluated the effects of dietary restraint on short-term appetite in response to manipulated palatability. DESIGN: The effects of palatability on appetite during a lunchtime meal were assessed by contrasting intake of a bland and palatable version of a simple food (within subject). To test how responses to palatability varied with restraint, these meals consumed by women were classified according to restraint (R) and disinhibition (D) scores from the Three-Factor Eating Questionnaire (TFEQ) as high R/high D (HR-HD), high R/low D (HR-LD), low R/high D (LR-HD) and low R/low D (LR-LD). SUBJECTS: A total of 40 normal-weight women subdivided into four groups based on TFEQ scores. MEASUREMENTS: The overall intake, appetite and hedonic ratings before, during and after the meal. RESULTS: All groups ate similar amounts of the bland food, but the LR-HD group ate significantly more of the palatable version than the other groups, whereas HR-LD did not increase intake in response to palatability. Hunger increased on tasting the palatable food in all but the HR-LD group, and this group ended both meals more hungry/less full than the others. CONCLUSION: Women classified as HR-LD were unresponsive to manipulated palatability, whereas those classified as LR-HD were over-responsive. These findings imply that some individuals are prone to over-respond to palatability and so are at greater risk of developing obesity, whereas others are able to resist the effects of palatability and so successfully self-restrict their food intake. Implications for obesity are discussed.

When caffeine consumers repeatedly experience a novel flavoured drink containing caffeine, the rated pleasantness of the drink flavour increases progressively. These results could be interpreted in terms of the flavour acting as a Pavlovian conditioned stimulus (CS) predicting the consequences of caffeine ingestion. However, all studies of this phenomenon to date have used between-subjects designs, and one criticism of this is that changes in pleasantness might have arisen from nonspecific effects. A more rigorous test is to examine changes in pleasantness for two drinks, a CS+ flavour paired with caffeine and CS- paired with placebo. Accordingly, 20 moderate caffeine consumers consumed both CS+ and CS- drinks in counterbalanced order over eight conditioning trials at breakfast, with hedonic and sensory characteristics evaluated on each trial. As predicted, the rated pleasantness of the CS+ drink increased whereas pleasantness of the CS- drink did not change. Despite this, participants did not have an overall preference for the CS+ flavour posttraining. However, both those who chose the CS+ and those who chose the CS- at the end showed the same direction and rate of change in pleasantness for the two drinks during training, but spurious differences in baseline preference obscured this effect in terms of an overall change in preference. Overall these data suggest that changes in pleasantness of drinks paired with caffeine delivery are best explained in terms of Pavlovian, associations between drink flavour and the postingestive effects of caffeine.

These data suggest that the ability of caffeine to reinforce changes in flavour liking are driven by the alleviation of withdrawal symptoms among habitual caffeine consumers and provide further support for the negative reinforcement theory.

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