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.
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
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)
Crossover
Pleasant Food Odor Stimulation
BehavioralExposure to an experimentally selected appetitive food odor (madeleine odor) delivered using a programmable ScentRealm collar in a standardized test room beginning at T-10 minutes before OGTT.
Control Environmental Condition
BehavioralStandardized testing environment identical to the experimental visit but without diffusion of the appetitive food odor.
Within-subject difference in glucose incremental area under the curve (iAUC) from 0 to 120 minutes during OGTT
Primary endpoint is the mean within-subject difference between food odor and control conditions in glucose incremental area under the curve from 0 to 120 minutes after oral glucose ingestion. Glucose iAUC will be calculated using the trapezoidal method, baseline-adjusted to glucose at T0. The main analysis will also assess the interaction between condition (odor vs control) and metabolic status (no overweight/insulin-sensitive vs obesity with low-to-moderate insulin resistance). Unit should be specified in the statistical analysis plan according to assay reporting (for example mmol/L×min or mg/dL×min).
Preabsorptive and early post-ingestion insulin iAUC as a measure of cephalic phase insulin release
Incremental area under the curve for insulin during the pre-ingestion and early post-ingestion period (0 to 15 minutes), compared by condition and metabolic status. Additional CPIR-related metrics include latency, peak concentration, slope, and percentage of responders. Unit to specify according to assay output (for example µIU/mL×min or pmol/L×min).
Preabsorptive and early post-ingestion C-peptide iAUC
Incremental area under the curve for C-peptide during the pre-ingestion and early post-ingestion period (0 to 15 minutes), compared by condition and metabolic status. Additional metrics include latency, peak concentration, slope, and percentage of responders. Unit to specify according to assay output.
Glycemic kinetic response during OGTT - Δmax
Effect of condition and metabolic status on glycemic maximum change from baseline (Δmax)
Glycemic kinetic response during OGTT - Time to peak
Effect of condition and metabolic status on the necessary amount of time to reach glycemic peak in minutes
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