Oral exposure and sensory-specific satiety
Introduction
As a food is consumed to satiety, its perceived pleasantness of taste declines compared to that of foods that have not been consumed. This phenomenon is referred to as sensory-specific satiety [1]. These declines in pleasantness of taste are greatest within the first 20 min following consumption, suggesting that these effects are primarily based on sensory cues, and less on postingestive or postabsorptive cues. Sensory-specific satiety promotes the consumption of meals with greater nutrient variety and thus may lead to increased intake [1], [2]. The magnitude of sensory-specific satiety of a specific food is dependent on its texture, flavour and colour [3], [4]. Although it has been reported that the macronutrient composition of a food also appears to influence its sensory-specific satiety [5], [6], [7], [8], [9], [10], the time framing of SSS and the finding that one does not need ingestion suggest that SSS is a sensory-based phenomenon [4], i.e. foods high in protein, sweet carbohydrates and fatty acids have been suggested to have a relatively greater sensory-specific satiety [6], [7], [11], [12], [13], [14]. Accordingly, Modified Sham Feeding (MSF) showed that the specific metabolites triggered by sensory perception give rise to sensory satiety [15]. Experiments using oral stimulation may shed some light on the consequences of vagal stimulation with food. Previous oral stimulation experiments using the MSF technique have revealed effects on metabolites, hormones and satiety [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]. MSF experiments performed by Mattes and Jackson and colleagues have shown that fat can be tasted [17], [19], [20], [21], [22], and had subsequent effects in particular with butter compared with after oral exposure to fat replacers [20]. Studies investigating the relative contribution of oral, gastric and intestinal exposure to food on satiation and satiety have shown that orosensory information is essential in the process of satiety development and appetite regulation. Oral exposure to food enhances the effects of gastric and intestinal exposure to food on appetite and subsequent food intake [27], [28], [29], [30].
Experiments performed by Rolls et al. gave insight in the neural mechanisms of sensory-specific satiety. They have shown that the identity of the taste is represented in the primary taste cortex, and the hedonic quality of the taste is computed and represented in the secondary taste cortex [31], [32], [33]. In humans the orbitofrontal cortex seems to be related to the hedonic evaluation of a food and thus to sensory-specific satiety.
In addition to sensory-specific satiety for a food eaten to satiety, other forms of sensory-specific satiety have been observed such as olfactory and visual sensory-specific satiety [4], [34]. In an experiment conducted by Rolls and Rolls chewing foods, without swallowing them, for as long they would be eaten in a meal, was enough to produce sensory-specific satiety [4]. However, the decrease in pleasantness of taste of the chewed food was not as large as the decrease in pleasantness of taste of the eaten food. In this experiment also a significant reduction in the intensity of both the taste of the chewed and eaten food was observed. The authors conclude that olfactory stimulation together with food in the mouth is, at least partially, able to produce sensory-specific satiety, without the presence of food in the gastrointestinal system.
In a recent experiment we observed a short increase in feelings of satiety following oral fat stimulation (without food ingestion) in the postprandial state [15]. This short increase in rated satiety following MSF is probably the result of the cephalic response in the satiety cascade. We hypothesised that this short increase in rated satiety is mainly sensory in nature. Therefore we approached the issue by analyzing the possible difference in SSS between after a food is sham-fed and after it is eaten.
Sensory-specific satiety appears to play a role when offering subjects a variety of foods that may be identical in composition, but differ in sensory properties; this increases food and energy intake [35]. Interestingly, in all of the experiments comparing ad libitum food intake of variety of foods to ad libitum food intake of a single food which have assessed subjective appetite sensations, changes in feelings of hunger and satiety do not differ between eating until satiated on a single course meal from eating until satiated on a multiple course meal; variety increased intake, while there was no diet effect on hunger ratings [36], [37], [38].
Hence, appetite sensations and taste perception may mainly contribute to the complexity of sensory-specific satiety, but to what extend and do they interact? To investigate the sensory role in sensory-specific satiety we made a distinction between oral exposure (in this experiment Modified Sham Feeding also referred to as ‘chewed’) and oral exposure plus gastrointestinal exposure (in this experiment eating). We studied sensory-specific satiety and changes in the appetite profile as well as changes in taste perception in a two-course meal comparing Modified Sham Feeding to eating the meal.
Section snippets
Subjects
Twenty-four subjects were recruited for this study (6 males and 18 females). The subjects were screened on health, medication, smoking and dieting parameters; they had to be normal weight and dietary unrestraint. The subjects had a mean ± S.D. age of 23 ± 6.9 years, and had a BMI of 22.2 ± 1.3. Their mean ± S.D. restrained eating score on the Three Factor Eating Questionnaire of the female and male subjects was 3.3 ± 3 and 2.0 ± 2.1, respectively [39]. All subjects were healthy, not taking medication,
Results
The subjects rated the palatability of the soup and the salad, which were completely novel to them, 65 ± 16 mm and 68 ± 16 mm, respectively. The weights of the MSF meal before and after chewing were compared; this yielded a mean (± S.E.M.) recovery rate of 101.8 ± 8.7%. The average number of spoons of soup was in both conditions (MSF and eating) 24 ± 5 spoons. The average number of bites of salad was in the MSF condition 26 ± 8 bites and in the eating condition 32 ± 8 bites (p < 0.02, unpaired Student's t
Discussion
The definition of sensory-specific satiety (SSS) states that when a food is consumed to satiety, its perceived pleasantness of taste declines compared to that of foods that have not been consumed. It appeared that SSS also occurred when not every aspect of the original definition is present. Even when a food is eaten, but not to satiety SSS occurred, which was the case with the soup as well as with the salad. Moreover, even in the case of the MSF salad SSS also occurred. It is likely that
Acknowledgements
We thank Chantalle Moors for her contributions to the study.
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