Sniffing madeleines before a sugar drink: can a pleasant scent change your blood sugar response?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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