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The study protocol was carefully designed to measure a range of variables associated with taste preferences and eating behaviours, with careful consideration given to potential limitations. The age matching of participants during recruitment was

successful, thereby negating the potential effects of age related differences in sweet taste preferences between overweight and lean groups (Desor & Beauchamp, 1987; Yoshinaka et al., 2016). In addition, all participants attended a screening visit prior to their assessment day and were excluded if the study foods were disliked. This enabled participants to exclude images of food within the LFPQ that were disliked and would not be freely chosen, allowing researchers to include appropriate images. This thereby served to improve the internal validity and accuracy of the findings of the LFPQ.

In the present study, visual analogue scales were used in the measurement of

subjective palatability ratings in response to a sweet and savoury food. All participants were provided with the same training for completion of the VAS, and so this is unlikely to explain the lack of differences between BMI groups in Chapter 4. Examination of the reproducibility and validity of VAS has been shown to be reliable in studies utilising a single meal (Flint, Raben, Blundell, & Astrup, 2000) and although their use has been most extensively validated for sensations of appetite such as hunger, their use in sensory and hedonic research although common, is less well validated.

The use of VASs within the present was given careful consideration as despite being consistently used within appetite research there is work suggesting that they are not a sufficient measure for determining between group differences, particularly when

groups are differentiated on the basis of body weight (Pepino & Mennella, 2012). It has been postulated that anchors on a VAS may be viewed differently between groups, particularly when the group’s sensitivity to what is being measured differs (Bartoshuk, Duffy, Hayes, Moskowitz, & Snyder, 2006). To illustrate this, in a study which

compared pain intensities, men and women were provided with a VAS anchored by ‘no pain’ and ‘most intense pain ever experienced’. For women, the label ‘most intense pain ever experienced’ denotes a much greater pain than it does for men which was reflected in the results (Dionne, Bartoshuk, Mogil, & Witter, 2005). A general labelled magnitude scale (gLMS) has been proposed as a more sensitive measure. Spaces between labels on the scale are adjusted to provide ratio properties (i.e. a ‘sweetness intensity’ rating of ‘50’ would be perceived twice as intense as a rating of ‘25’) and as a consequence it is a more sensitive measure to the differences in subjective ratings across different groups (Bartoshuk et al., 2006). However, during the screening session all participants were trained on the use of VASs by a qualified experimenter which is believed to negate these issues.

Assessment of energy and nutrient intake in a laboratory setting provides a high level of experimental control. This method has numerous benefits as it facilitates the

implementation of precise experimental manipulation of variables thereby supporting a high degree of precision. However, the artificial environment is also capable of

constraining a participant’s behaviour and so there is a careful balance to be struck between precision and naturalness (Blundell et al., 2009). It should be clearly stated that appetite assessment within the laboratory does not attempt to replicate feeding conditions within the participant’s natural environment, rather it provides a platform to measure eating behaviour free from social chaos and confounding factors (Blundell et al., 2009). However, in the present protocol eating behaviour assessment was

assessed via both ad libitum test meal and habitual dietary intake, thereby providing a picture of both single meal intake in a controlled environment, as well as free-living intake in a more natural setting.

The ad libitum food items were chosen due to their representation of typically consumed foods, were commercially available food items and were homogenous foods rather than typically portioned foods (e.g. sandwiches). This is a benefit of the protocol, increasing the validity of the results and conclusions drawn. For this reason, despite the meal being ingested in an artificial and unfamiliar environment it was as close to a typically consumed lunch meal as possible. Moreover, the two foods were closely matched for energy density and so differences in satiation that may have resulted due to consumption of different proportions of the savoury and sweet foods were minimised.

Retrospective methods of assessing dietary intake are flawed in their measurement of a participant’s memory of past diet, rather than the diet itself (Krall, Dwyer, & Ann Coleman, 1988). As a consequence, validity is reliant on accurate and honest recall by participants. Moreover, in women the accuracy of self-reported dietary recall is

negatively impacted by social desirability (Hebert, Clemow, Pbert, Ockene, & Ockene, 1995). In order to provide an estimation of the incidence of under-reporting the

Goldberg cut-off was employed (Goldberg et al., 1991). The mean TEI/RMR within the present data set was 1.29; a figure lower than expected and indicative of under-

reporting, as previous research has suggested a figure of 1.2 is indicative of being bed bound and motionless (Black, Coward, Cole & Prentice, 1996) and the WHO’s value for ‘light activity’ is 1.55 (WHO, 1985). The under-reporting may be due to a bias whereby participants reduce intake whilst actively monitoring their intake (Lissner, 2002). However, as there were no differences between groups in the extent of under- reporting this is likely not a major issue within the present analyses, although any conclusions drawn should be taken with caution.

Although there are limitations to assessment of habitual dietary intake, MyFood24 has been specifically developed for use within research environments and has been demonstrated as suitable for use in UK adults. It is the first online 24-h dietary assessment tool for UK populations with a food composition database specifically designed for its use (Carter et al., 2015). In addition to this, data obtained via MyFood24 has been shown to be as reliable as that collected via interviews (Albar, Alwan, Evans, Greenwood, & Cade, 2016). Therefore, despite there being a deal of under-reporting within the current sample, MyFood24 is believed to provide a valuable insight into the habitual dietary intake of participants. Furthermore, providing there is an acknowledgement of the limitations of the assessment of haitaul dietary intake, it has been concluded to provide valuable information regarding habitual dietary patterns that can be used to inform research (Subar et al., 2015).

A final limitation is that BMI was examined as the potential moderator of the

associations between taste preferences and eating behaviour variables. Future work may wish to consider a more direct measure of adiposity such as %BF; however as previously outlined this would not enable comparison with studies that have used BMI as a method of categorising participants. If body composition is shown in future work to be a poor moderator of these associations, psychological traits such as eating restraint or craving control, may additionally be explored as potential moderators due to their higher incidence in overweight and obese individuals (Chao, Grilo, White, & Sinha, 2014; Snoek, van Strien, Janssens & Engels, 2008; White et al., 2002).