OLFactory Odour Stimulation and FOOD Preferences

The aim of the present "OLFO-FOOD" clinical trial is to investigate, if olfactory stimulation impacts food choice, reference and calorie intake in humans with obesity assessed using a test buffet.

Overweight study participants will be included in this study. For the participants the study consists of the screening visit and main visit 1 and 2. In between the main visits there is a wash-out period of 1 week (7 days ± 3 days). In total, participants will have 3 visits. After the screening visit and before the main visit 1, odours will be assigned in a randomized order. Each participant will receive both odours. The two visits (main visit 1 and 2) will have the exact same procedures except for the olfactory odour.

Hunger, appetite, thirst, food perception, nausea, headache and mood will be assessed and the first blood samples will be collected. The participants will receive the aspUraclip® filled with 50 μl of either olfactory stimulation or placebo (propylene glycol), due to the computer-generated randomization order. The "aspUraclip®" will be clipped to the nasal septum for 15 minutes. After olfactory stimulation, vital parameters will be measured and blood samples will be taken. Participants will rate hunger, appetite, thirst, nausea, headache, mood, as well as local nose irritation, odour intensity and odour perception. Directly afterwards, the participants choose food ad libitum from a test-buffet. Participants will have 2 hours to eat from the buffet, but can finish earlier if they wish. Eating time will be recorded. After finishing their meal, vitals will be measured, blood samples will be collected and the participants will rate hunger, appetite (general, carbohydrates, meat, dairy foods, vegetables, fruits, sweets, salty foods), thirst, nausea, headache, mood, food taste, food taste intensity, food scent intensity and food scent perception on a 10-point VAS (visual analogue scale). 2 hours after the start of the test-buffet, patients will rate the same questions on a VAS again, vitals and blood samples will be taken. If the participants eat throughout the 2-hour-timespan of the test-buffet and don't stop early, there will be only one measurement (vitals, VAS, BS) after 2 hours, when the test-buffet ends. Food intake will be measured by weighing the food before and after consumption. Following the test-buffet, patients will have a resting phase of 2 hours. During this phase, patients are free to read, listen to music or similar. After the 2 hour resting phase, vitals will be measured, blood samples collected and VAS-questions asked.

Eligibility Criteria:
Inclusion Criteria:

* Age 18-60 years
* Written informed consent
* BMI ≥30 kg/m2
* Normosmia (as defined by Sniffin' Sticks Test)

Exclusion Criteria:

* Known allergy to olfactory stimulation substance, citrus fruits, citrus flavours, citrus food products
* Lactose-intolerance, celiac disease or non-celiac wheat sensitivity
* Diet other than omnivore or vegetarian
* Eating disorder (now or in the past)
* Dysphagia
* Acute disease affecting food intake
* Acute upper respiratory tract infection, acute or chronic sinusitis
* Severe visual impairment (vision \<10%)
* Surgical intervention of the nasal cavity or the paranasal sinus
* Current illicit drug abuse including daily marijuana and CBD (Cannabidiol) consumption (alcohol ≤2 drinks per day allowed)
* Any kind of severe chronic disease (e.g. severe heart failure, active cancer disease)
* Type 1 and 2 diabetes mellitus
* Treatment with insulin-sensitizing drugs within the last 3 months
* Treatment with Glucagon-like Peptide 1 (GLP1)-analoga
* History of neurodegenerative diseases, severe head trauma
* Severe renal impairment (e.g. estimated glomerular filtration rate \<30 ml/min/m2)
* Known liver cirrhosis or other severe liver impairment
* Use of any kind of decongestant more than twice a week
* Uncontrolled dysthyroidism
* Uncontrolled hypertension
* Regular use of psychopharmaceutic drugs
* Study participants aims to start a new diet or exercise program during the study
* Bariatric surgery
* Pregnancy/Lactation
* Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc.
* Participation in an interventional study within the last 3 months