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Background and aim Unhealthy eating habits such as unhealthy food choices or overeating increase the prevalence of obesity, diabetes, cancer, cardiovascular and other diseases. Therefore, it is important to understand how separate factors, such as sensory processes, influence our eating behaviour. As one of the sensory modalities, olfaction has a relationship with food intake regulation. Previous research reveals that food odours can induce both appetite and satiation. In this thesis, we split appetite and satiation into a ‘general’ part and a ‘food specific’ part. General appetite and general satiation refer to the desire to eat in general. General satiation measured by subjective ratings (e.g. by using line scales) is also named ‘subjective satiation’. The specific part refers to the desire to eat a specific food: e.g. the appetite for a banana or the appetite for tomato soup. The main objective of this thesis was to investigate under which circumstances odours are appetizing or satiating in order to identify factors that influence our eating behaviour.Odours arrive at the odour receptors via two routes: the orthonasal route via the nose to perceive the outside world or retronasally via the mouth to ‘taste’ the food. The appetizing and satiating effects of ortho- and retronasally smelled odours were investigated by varying the odour exposure time, the odour concentration(retronasal only), the odour type, passive versus active sniffing (orthonasal only) and by switching between odour types. Methods We conducted six within-subject experiments. All participants were healthy normal-weight women (age 18-45 y and BMI 18.5-26 kg/m2). In four experiments (studies 2A, 2B, 3A and 3B), we investigated the appetizing and satiating effects of orthonasal odours, with two experiments addressing odours that were smelled passively in rooms with ambient odours (chapter 2) and two addressing actively smelled odours by sniffing the contents of a cup (chapter 3). In studies 2A (passive, n=21), 2B (passive, n=13) and 3A (active, n=61), we investigated the effects of exposure timeand odour typeon appetite, the appetite for specific foods, food preference and food intake. Differences between passiveand active exposure were investigated by comparing the data from 2A and 3A. In the fourth experiment (n=30) using a similar set-up, sweet and savoury odours were presented directly after each other, to explore the effects of daily encounters with a variety of food odours (i.e. switching). In all orthonasal studies, general appetite and the appetite for specific foods were monitored over time, using visual analogue scales. General appetite comprised hunger and desire-to-eat ratings. The appetite for specific products addressed the appetite for smelled products and the appetites for a set of other products that were congruent and incongruent with the odour (studies 2A, 2B, 3A and 3B). Food preference was assessed using a computerised program offering pairs of food pictures (studies 2A, 2B and 3B). Furthermore, two experiments addressed the satiating effects of retronasal odours while consuming tomato soup ad libitum (studies 4A and 4B). The retronasal odour exposure was disconnected from the soup base consumptionby use of a retronasal tube that was connected to an olfactometer. The odours were delivered directly into the nasal cavity at the moment a sip of soup base was swallowed. In study 4A (n=38), the satiating effects of odour exposure time(3 and 18 s) and odour concentration(5x difference) were investigated. In study 4B(n=42),we investigated whether addition of cream odourto tomato soup, in combination with a low or high viscosity, affected satiation. Hunger and appetite ratings were monitored over time during odour exposure, by using 100 mm visual analogue scales (VAS). Results The results showed that orthonasalexposure to food odours influenced the appetite for specific foods via a typical pattern: the appetite ratings for the smelled foods increased by +6-20 mm(SSA; all P |
