The goal of this clinical trial is to investigate the abundance of a natural odour in human cerebrospinal fluid in obese and lean participants after inhalation thereof. Participants will undergo blood sample collection and inhalation of either a natural odour or placebo through an inhaler in addition to a liquor puncture prescribed in standard of care context.

Inclusion Criteria Obese Participants:

• Age 18-60 years
• Written informed consent
• Scheduled for routine liquor puncture
• BMI ≥ 30 kg/m2
• No proven diagnose of diabetes

Inclusion Criteria Lean Participants:

• Age 18-60 years
• Written informed consent
• Scheduled for routine liquor puncture
• BMI 18-25 kg/m2

Exclusion Criteria:

• Known allergy to the natural odour
• Acute upper respiratory tract infection, acute or chronic sinusitis
• Present or past surgical intervention of the nasal cavity, the paranasal sinus, the pituitary or the frontal brain
• Pregnancy/lactation
• Any kind of severe chronic disease (e.g. severe heart failure, active cancer disease, severe renal impairment with an estimated glomerular filtration rate <30 ml/min/m2)
• Inability to understand the study procedure and to sign the study consent