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NutrInsight • Satiety: from appetite sciences to food application
1.2 Assessing the various aspects of satiety
The homeostatic toolbox
Various methods have been developed to assess the satiating power of a food, either at the time of ingestion (satiation), or in the hours that follow intake (satiety). A valid assessment of satiety involves adequate measurement of several aspects of behaviour that are considered the expressions of satiety. These include sensations of hunger, fullness, or desire to eat on the one hand, and changes in meal size or food selection under the influence of prior eating on the other hand. In some studies, post-meal satiety is measured as the duration of the interval until the return of hunger and the subject’s self-determined onset of the next meal. For all these aspects, a set of principles have been established and constitute a strong methodology for measuring these aspects of appetite control.
The experimental study of satiation and satiety requires converting the daily eating pattern into an experimental protocol. The daily eating pattern of meals and snacks is accompanied with fluctuations of hunger and satiety sensations. In order to determine the satiating power of a food or meal, both the size of eating events and subjective sensations need to be quantified in a valid reproducible fashion. The validity of experimental methods in this field has been reviewed in recent publications [e.g. Blundell et al., 2009; Blundell et al., 2010]. Under controlled conditions, when test meals are served under repeated identical conditions at a fixed interval following an identical earlier meal, the reproducibility of the measurement of ad libitum energy intake is high, regardless of prior diet standardisation [Gregersen et al., 2008]. Visual Analogue Scales (VAS) are used for assessing the intensity of satiety-related subjective sensations such as “hunger”, “fullness”, or “desire to eat” for example. The reproducibility of VAS scales for the assessment of appetite sensations before and after a meal has also been confirmed. In a study examining the VAS ratings of appetite sensations before breakfast and every 30 minutes during a 4.5 h postprandial period under identical conditions, the profiles for satiety, hunger, fullness, and prospective consumption were similar over two successive test days and no statistically significant differences between test days were found [Flint et al., 2000].
When large scale trials are carried out to investigate the effects of interventions on satiety, it is paramount to efficiently monitor large amounts of data. Since appetite sensations (hunger, fullness, etc.) are rapidly oscillating states, the acquisition of repeated ratings has been facilitated by the use of new hand-held electronic devices to obtain frequent VAS ratings of sensations, such as the recently validated hand-held Electronic Appetite Ratings System (EARS) [Gibbons et al., 2011].
The following chapter, by Dr Sophie Vinoy, illustrates further developments of appetite assessment via the training of “satiety expert” panels, based on methods used in sensory analysis.
The Hedonic toolbox
There are many dimensions to the motivation to eat. Research of the last decades has highlighted the difference between two critical aspects: liking for particular foods is different from the momentary wanting of the same foods. This distinction can be manifested in both explicit and implicit processes [Finlayson et al., 2007b].
Liking vs. Wanting
Liking represents the pleasure or reward aspect of food. By contrast, wanting is the motivational component – also known as the “incentive salience” of food. Wanting adds the compulsive element to eating.
Liking and wanting can be dissociated methodologically by asking subjects different questions: the question “How much do you like this food?” is not equivalent to the question “Which food would you most want to eat now?”. These different aspects of the attraction to foods have separate neural substrates and correspond to different brain pathways [Berridge, 2009].
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