Specificity of Flavor-Nutrient Learning: An fMRI Experiment

Study design and Participants The investigators randomly assigned participants to consume one of two novel flavored, high-sugar beverages daily for a 3-week period. The study included fMRI and behavioral assessments pre-/post-intervention and 9 study visits during the intervention period. 20, healthy-weight, young adults (10 female, 10 male; x̅ age = 23.3±3.4; x̅ BMI = 22.1±1.9; 5% Hispanic,10% Asian/Pacific Islanders, 85% European Americans) completed protocol seen in Figure 1a. Exclusion criteria were a body mass index (BMI; kg/m2) <18.5 or >26.5, sweetened (artificial or caloric) beverage consumption > 6 times/week, tobacco/e-cigarette use > 6 times/week, psychoactive medications or drugs more than > 1 time/month, pregnancy, head injury with a loss of consciousness, significant cognitive impairment, major medical problems, endorsement of disordered eating or current Axis I psychiatric disorder as assessed by online screener. Participants provided written informed consent; methods and procedures were approved by University of North Carolina at Chapel Hill's Institutional Review Board.

Intervention Interested participants completed a brief online screening survey those that appeared to qualify were scheduled for the baseline visit where inclusion and exclusion were confirmed and consent was reviewed and obtained. Participants were randomly assigned to one of the two juice conditions, stratified by sex. Once consented, participants completed the behavioral and perceptual measures at the baseline behavioral assessment. On a separate day participants completed the baseline neuroimaging assessment. The day following the neuroimaging assessment participants began the intervention period where they consumed their assigned juice daily for the 3-week period. During the intervention period participants came to our lab every Monday, Wednesday and Friday (9 total assessments) to: consume a portion of that day's juice in the lab, complete perceptual measures and a weight assessment, pick up the following day(s) juice, and return the empty bottles from the previous day(s). On Fridays, participants were given two bottles to consume and instructed to consume one per day and return the bottles on the following Monday. Empty bottles were returned to increase compliance. The follow-up neuroimaging assessment was scheduled such that participants completed the 3-week intervention, did not consume a juice for 24 hours and then were scanned. The follow-up behavioral assessment occurred within three days of the follow-up scan Figure 1b.

Beverages were selected to be: sweetened from sugar, i.e., not include high fructose corn syrup, and/or artificial sweeteners, have no artificial flavors, colors or preservatives, calorically equivalent to common sugar-sweetened beverages (e.g., soft drinks), be caffeine- and texture-free, and generally novel in flavor. The juices were eucaloric, had similar palatability, and easily distinguishable from one another. Prior to study initiation, pilot taste testing was completed in a small sample to insure both the novelty and equal palatability of the two juices to be included in the study. The resulting two beverages were: Apple-Cherry-Berry juice and Orange-Tangerine-Passionfruit juice. The 10 fl oz bottles of juice each contained 133 kcals, 31g of sugar. The juice logos were selected to be novel, of similar visual complexity, both in black and white, convey no information beyond a unique symbol, yet be easily distinguishable from one another. Each juice was presented in individual 10 fl oz bottles with the only identifier a sticker of the associated logo.