Mixed messages: Assessing interactions between portion-size and energy-density perceptions in different weight and sex groups.

INTRODUCTION: Food portion size (PS) and energy density (ED) are the two primary determinants of total energy intake. While emerging neuroscientific data indicate judgments of PS and ED involve distinct brain regions, it is not understood how these judgements interact with each other to influence an individual's energy consumption. The present study investigated these cognitive interactions against body-mass-index (BMI) and sex. METHODS: We tested 70 participants (including 34 overweight individuals) for cognitive biases when judging PS and ED, using the Garner task paradigm. Participants were asked to discriminate PS and ED, following pre-determined cognitive rules. Reaction time and correctness of their responses were recorded and analysed against the testing conditions across sexes and BMI groups. RESULTS: We detected a significant 3-way interaction between BMI, Task, and Condition (F(3, 67) = 4.1, p = 0.047, ƞ2 = 0.06). Post-hoc tests suggested that, in the PS task, both weight groups experienced the Garner Interference effect introduced by variations of ED. That is, when making judgments concerning PS, participants were unable to ignore information relating to ED. Results from the ED task differed across weight groups, with only the overweight group being susceptible to the Garner Interference introduced by variations of PS. Additionally, both Sex and BMI were significant factors moderating reaction time when judging PS. Significantly longer reaction time was observed in female versus male comparisons, and for overweight versus healthy-weight participants (p < 0.05). CONCLUSION: Overall, the results confirmed cognitive interactions involving PS and ED, although these interactions were asymmetric across BMI groups. These findings provide new insights into the cognitive processes underpinning individual dietary decision-making, and are potentially important for developing targeted intervention strategies for effective management of unhealthy eating behaviour.

Expectancy versus experience - Comparing Portion-Size-Effect during pre-meal planning and actual intake.

Research on eating behaviour has confirmed that portion size can substantially influence intake, a phenomenon known as the Portion-Size-Effect (PSE). Despite extensive research interest, there is limited understanding about the PSE on intended consumption (often measured by Expected Intake). It also remains unclear whether the presentation of food cues (e.g., Word Descriptors; Food Images) can modulate PSE during pre-meal planning. The current study addressed these questions by comparing PSE on intended versus actual consumption, with 62 participants based on a within-subject design. Participants firstly rated Expected Intake for a pasta dish of three sizes (400, 600, and 800 g), with each size presented in three different formats of food cues. The participants' actual pasta intake with the three portion sizes was tested in three ad libitum sessions over 7 weeks. The results suggested that Expected Intake increases as portion size becomes larger, following a nearly linear relationship. In comparison, the Actual Intake had a smaller increment after the presented portion size exceeded the 'appropriate' range. Relating to these results, the pre-meal PSE was found to be comparable to the actual PSE with moderate portion sizes (i.e., 600 g-400 g), but significantly stronger than the actual effect with large portion sizes. Overall, our data support the hypothesis that portion size can have a stronger influence on meal planning than actual food intake, and show that the format of food cues has considerable influence on Expected Intake. Studies of pre-meal planning should carefully consider the role of portion sizes and food cues on Expected Intake.