SENSILINS: Impact of Cephalic Phase Insulin Release Induced by an Environmental Food Odor Stimulus on Glucose Homeostasis According to Insulin Sensitivity Level (SENSILNS)

Inclusion Criteria

• Age 18 to 50 years inclusive
• Stable body weight during the previous 3 months (±5% of total body weight)
• Willing to comply with the full study protocol
• Sedentary lifestyle or stable regular physical activity, with agreement to keep this unchanged throughout the study
• Able to understand study information, read and write French, and provide written informed consent
• Affiliated with a social security scheme or equivalent
• Non-smoker and non-vaper
• Willing not to take dietary supplements, probiotics, prebiotics, or laxatives for 10 days before each visit
• For women of childbearing potential: negative serum pregnancy test; not pregnant and not breastfeeding
• Mean score between 1 and 2 on the 3 specific CiTAS questionnaire statements used as inclusion criteria
• ETOC flash olfactory screening: able to detect the odor-containing vial among 4 presented vials for all 7 odors tested
• Able to identify the madeleine odor used in the study
• Rated pleasantness/appetence of the madeleine odor above 1/9
• For the no-overweight group: BMI 19 to <25 kg/m² and HOMA-IR <1.7
• For the obesity group: BMI 30 to <35 kg/m² and low-to-moderate insulin resistance based on HOMA-IR [protocol inconsistency to resolve; see note below]

Exclusion Criteria

• Unstable medical or psychological conditions that could impair compliance, safety, or study participation in the investigator's judgment
• Alcohol consumption >30 g/day, or established abuse/dependence on another drug
• Ongoing exclusion period from another study listed in the national volunteer file
• Legal protection measure (guardianship/curatorship)
• Deprivation of liberty by judicial or administrative decision
• Exceeded annual compensation limit for research participation
• Lack of valid required health documentation in the event of exceptional governmental epidemic measures
• Blood donation within 2 months before inclusion visit
• Limited venous access making repeated blood sampling/catheter placement difficult
• Current or permanent anosmia or olfactory disorder
• Type 1 or type 2 diabetes, treated or untreated
• History of gestational diabetes
• Known or treated hypertension
• Blood pressure >160 [unit missing; likely mmHg systolic threshold]
• Dyslipidemia, treated or untreated
• Triglycerides >3 mmol/L
• Allergic rhinitis
• Nasosinusal polyposis
• History of intestinal or abdominal surgery except appendectomy or simple hernia repair
• History of ENT or neurological surgery
• Severe eating disorder (for example anorexia, bulimia, binge-eating disorder, night eating)
• Any pathology detected on clinical examination or medical interview judged by the investigator to interfere with study endpoints or participant safety
• Any biological abnormality judged by the investigator to interfere with study endpoints or participant safety
• Use of treatments likely to interfere with study measurements, for example antidepressants, antiepileptics, neuroleptics, CPAP treatment for sleep apnea, nasal spray medications, or anti-obesity drug treatment, according to investigator judgment