Influence of macronutrient-related odours exposure on (congruent) appetite and actual food intake.
Cover story (for information brochure): Influence of odour exposure on alertness.

Living in an obesogenic environment, we are surrounded by food odour cues that
trigger these unconscious decisions and induce us to (over)eat. Olfaction plays
an important role in eating behaviour by detecting foods, attracting our
attention, and triggering our appetite. However, the effect of food odours on
subsequent behavioural responses remains unclear.
Olfaction may play a role in appetite and meal initiation. Some studies have
suggested that food odors increases appetite for foods with similar properties,
sensory-specific appetite, and may generalize across foods within certain
categories as taste and energy-density.
On the other hand, contradictory findings have been reported between the
influence of odours on appetite versus actual food choice and intake.
Differences in intensity, type of exposure (explicit or implicit), and
awareness of the odour cue could be responsible for the lack of consistency in
these findings.
Therefore, we propose a series of behavioural studies to extend the knowledge
in the (macronutrient signalling) function of odours and its impact on appetite
and actual food intake. We aim to disentangle the differential effects of
intensity, exposure method (explicit and implicit), and awareness of the cue:
Aware and actively smelling of odours (part A); unaware (implicit) smelling of
odours (part B); unaware and passively smelling by means of ambient odours
(part C).
In the present protocol only part A will be explained in further detail. The
knowledge gained from Part A will be used to establish the proper methods for
part B and C.

The primary objectives of the current study are to determine the influence of
aware and actively smelled macronutrient-related odours on appetite, and actual
food intake, in normal weight and unrestrained individuals.
The secondary objectives of the current study is to determine the influence of
aware and actively smelled macronutrient-related odours on food preferences.
Also, we will determine the correlation between self-reported macronutrient
preference and actual macronutrient intake.

The current study is a counter-balanced cross-over intervention study.
Subjects will take part in an information meeting and five test sessions. In
each test session, subjects will be exposed to one of the five conditions
(odour representing food high in carbohydrates, protein and fat, low in
calories, and a no-odour) and tested for behavioural measures. In each test
session, subjects will be asked to rate their general and specific appetite, to
perform a computer-based task on food preferences (MTPRT) and an alertness task
(PVT). Participants will be provided with lunch to covertly measure ad libitum
food intake.

In each test session, participants will be exposed to one of the five
conditions (odour representing food high in carbohydrates, protein and fat, low
in calories, and a no-odour) for a few minutes.

This study is non-therapeutic. The risk associated with participation is
negligible. The burden can be considered as low. The study includes five site
visits in a non-satiated state and an information meeting (approx. total
duration of 6 hours). All odours and food products are considered safe to
use/consume and commercially available.