Does a pleasant food smell change blood sugar after a sugar drink?

Trial details

Who runs it

Hospices Civils de Lyon

Trial code

NCT07638111

Record updated

10 June 2026

Original description

This single-center, randomized, single-blind, 2-period crossover interventional study will evaluate whether exposure to a pleasant food odor 10 minutes before a 75 g oral glucose tolerance test (OGTT) modifies glucose homeostasis in adults with different metabolic phenotypes. Participants will undergo two experimental conditions in random order: food odor stimulation and control condition without odor, separated by a 4-week washout. The main objective is to quantify the within-subject effect of food odor stimulation on the incremental area under the glucose curve (iAUC) from 0 to 120 minutes during OGTT and to assess whether this effect differs according to metabolic status. Two predefined groups will be enrolled: adults without overweight and without insulin resistance, and adults with class I obesity and low-to-moderate insulin resistance. Secondary objectives include characterization of cephalic phase insulin release (CPIR), C-peptide and GLP-1 responses, glycemic kinetics, associations between CPIR and metabolic responses, and participant acceptability of the test environment and olfactory stimulation. A plasma biobank will be constituted from part of the collected samples for future research.Read full original descriptionShow less

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

This single-center, randomized, single-blind, 2-period crossover interventional study will evaluate whether exposure to a pleasant food odor 10 minutes before a 75 g oral glucose tolerance test (OGTT) modifies glucose homeostasis in adults with different metabolic phenotypes. Participants will undergo two experimental conditions in random order: food odor stimulation and control condition without odor, separated by a 4-week washout. The main objective is to quantify the within-subject effect of food odor stimulation on the incremental area under the glucose curve (iAUC) from 0 to 120 minutes during OGTT and to assess whether this effect differs according to metabolic status. Two predefined groups will be enrolled: adults without overweight and without insulin resistance, and adults with class I obesity and low-to-moderate insulin resistance. Secondary objectives include characterization of cephalic phase insulin release (CPIR), C-peptide and GLP-1 responses, glycemic kinetics, associations between CPIR and metabolic responses, and participant acceptability of the test environment and olfactory stimulation. A plasma biobank will be constituted from part of the collected samples for future research.

Inclusion: 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: Alcohol consumption >30 g/day, or established abuse/dependence on another drug; Blood donation within 2 months before inclusion visit; 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; Unstable medical or psychological conditions that could impair compliance, safety, or study participation in the investigator's judgment; Current or permanent anosmia or olfactory disorder; Type 1 or type 2 diabetes, treated or untreated; History of gestational diabetes; Known or treated hypertension; Allergic rhinitis; 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); Triglycerides >3 mmol/L; 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; Limited venous access making repeated blood sampling/catheter placement difficult; Blood pressure >160 [unit missing; likely mmHg systolic threshold]; Dyslipidemia, treated or untreated; Nasosinusal polyposis; 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.

ClinicalTrials.gov NCT07638111