Humans possess the ability to discriminate food fat content solely based on retronasal olfaction

Dietary fat overconsumption contributes to the development of obesity and related comorbidities; however, its sensory perception is poorly understood. Although humans can discriminate between vapor-phase fatty acids, both ortho- and retronasally, evidence of orthonasal fat discrimination in real foods is limited, and non-existent for retronasal olfaction. In two experiments, we investigated the human ability of olfactory food fat content discrimination in dairy milk and assessed whether this ability is affected by habitual dairy intake. Participants undertook a series of DR A-not A discrimination tests (analysed with R-index analyses) coupled with perceptual ratings and a questionnaire on dairy consumption habits. In the first experiment (n = 66), ortho- and retronasal discrimination was evaluated using dairy milk samples manipulated to contain 0%, 1.5% and 3.5% fat. Subjects could discriminate between all three fat levels orthonasally (p < .001), whereas retronasally they were able to do so between 0 and 1.5% (p < .001) and 0–3.5% (p < .001). The second experiment (n = 44) focused only on retronasal discrimination, using (manipulated) dairy milk samples of 3.5%, 7%, 10.5% and 14% fat. Here, discrimination was possible between 3.5 and 14% (p < .001) and 7–14% (p < .05) samples. No effects of total dairy fat intake, total dairy product intake or dairy exposure frequency were observed on discrimination ability in both experiments. This is the first study demonstrating that humans are capable of discriminating food fat content solely based on retronasal olfaction. Results also suggest that this ability is unaffected by habitual intake.