Vitis Intervention Trial in Substrate Metabolism

Recruitment Participants are recruited from the UAB/Birmingham catchment area (theUniversity of Alabama at Birmingham, the city of Birmingham, and Jefferson and ShelbyCounties) through research registries, clinic flyers, web‐based advertisement, theDepartment of Nutrition Sciences website, ResearchMatch, and word of mouth. Interestedindividuals contact study staff for an initial study overview and eligibility screener.Prescreening Interested individuals will contact study staff and receive an overview ofthe study and then provide verbal consent to answer questions for high level eligibility.This will include questions related to demographics, anthropometrics, current use ofnicotine and caffeine, claustrophobia, dietary adherence, use of smart phone/tablet,prescription drugs, chronic diseases and history of recent weight changes. If theinterested individual remains eligible and willing to participate, an in‐person screeningvisit will be scheduled.Screening Screening visits are scheduled in the morning (approximately 7 am ‐11 am), andparticipants must arrive fasted. After informed consent is provided and obtained,participants will then be asked to change into a gown for procedures of height, weight,REE by metabolic cart (Parvo TrueOne 2400), DXA (Lunar GE), blood draw to screen for WBCcount, and paperwork. Participants will then be provided with a weight scale and anorientation to the Healthie app. They will receive a study‐linked email address to loginto Healthie, no participant data will be provided to Healthie. Once they have reviewedoperations of their new scale and Healthie, they will then await WBC count confirmationand once the study team has that in place, weight stability data collection will startwith a calorimeter scheduled two weeks out.Randomization and Blinding Following confirmed weight stability, participants arerandomized to a grape‐first or placebo‐first sequence (AB or BA). Randomization and dosepreparation are performed by the metabolic kitchen, which maintains allocationconcealment; participants, investigators, and all other study staff (including theinterventionist) remain blinded throughout. Each dose consists of 72 g of freeze‐driedwhole California table grape powder or a matched placebo powder formulated to replicatethe sugar, fiber, organic acid, and sensory characteristics of the grape powder withoutpolyphenolic compounds. The grape powder is a whole‐food dietary supplement; noinvestigational new drug designation or clinical‐trial phase applies.Study Interventions/Procedures Study Design Single‐site, double‐blind,placebo‐controlled, crossover pilot study. Twenty adults (10 lean, 10 withoverweight/obesity) complete two identical 40‐hour stays (arrival evening plus one fullcalorimeter day) in the UAB Webb whole‐room indirect calorimeter, separated by a washoutperiod. Each participant receives both freeze‐dried whole California table grape powderand a matched placebo powder in random order.Safety During each session, participants are monitored by study staff for aberrant data(e.g., fidgeting). Hourly values of calorimeter temperature, pressure, and targetmetabolic rate and respiratory quotient are recorded. Safety procedures within thecalorimeter are reviewed with each participant prior to the start of each calorimeterday. For medical emergencies, the laboratory acts in accordance with University policy.Safety Procedures All calorimeter safety procedures are reviewed with each participantprior to the start of every calorimeter day. The calorimeter door can be opened from theinside at any time, and staff maintain continuous communication and monitoring throughintercom, call button, and video surveillance. As a 911‐response facility, trainedpersonnel are always present during calorimeter occupancy. An AED and first‐aid kit areavailable on site. In the event of a medical emergency, participants are promptly removedfrom the calorimeter, 911 is activated, and care proceeds in accordance with Universitypolicy. Environmental safety is ensured through continuous oxygen and carbon dioxidemonitoring with alarm systems, and the calorimeter ventilation can be rapidly purged ifneeded. All safety systems are tested before each study day. Participants may request toexit the calorimeter at any time for safety or comfort. All adverse events are documentedand reported per IRB policy.Safety Training and Oversight All study personnel are trained in emergency procedures,calorimeter operations, and participant monitoring. Staff complete a pre‐use safetychecklist before each study day to confirm function of alarms, communication systems,ventilation, and egress mechanisms. The Principal Investigator is responsible foroversight of safety protocols, review of any adverse events, and ensuring compliance withUniversity and IRB requirements.PROCEDURES:Pre‐ Screening: For the pre‐screening, interested individuals will contact study staffand receive an overview of the study and then provide verbal consent to answer questionsfor high‐level eligibility. This will include questions related to demographics,anthropometrics, current use of nicotine and caffeine, claustrophobia, dietary adherence,use of smart phone/tablet, prescription drugs, chronic diseases and history of recentweight changes. If the interested individual remains eligible and willing to participate,an in‐person screening visit will be scheduled.Screening Visit: At the screening visit, study staff provide a detailed overview andobtain verbal consent to collect eligibility information, including medical history, adietary polyphenol intake assessment, and standardized health questionnaires. Eligibleparticipants attend an in‐person screening visit at the UAB Webb Building to review andsign the informed consent, after which medical history and current medications arereviewed, height and weight measured, and a smart scale issued with instructions fordocumenting food, sleep, and physical activity.In Person Procedures:Informed Consent: Prior to enrollment, informed consent is obtained in accordance withthe Declaration of Helsinki and federal regulations (45 CFR 46), using the IRB‐approvedconsent document for this study. A trained study investigator reviews all procedures,risks, benefits, alternatives, and participant rights in a private setting, confirmscomprehension, and documents written consent by participant signature and date; a copy isprovided to the participant.Medical History Review and Screening: Comprehensive medical history is obtained atscreening to characterize participant health status and identify exclusionary conditions.Anthropometrics Body weight is measured with participant in gown/disposable exam shortsin triplicate after voiding, using a calibrated digital scale (precision ±0.05 kg). Theweight of the gown is also measured and substrate from the total weight. If two measuresvary by more than 0.2 kg, then a third measure is taken and all three are recorded.Height is measured once using a wall‐mounted stadiometer. Waist circumference will bemeasured in triplicate using a tensiometer to the nearest tenth of a centimeter.Body Composition Body composition (fat mass, fat‐free mass, bone mineral content) isassessed via dual‐energy X‐ray absorptiometry (DXA). These measurements permitnormalization of energy expenditure to metabolically active tissue mass and enhancereproducibility by ensuring comparable baseline conditions across repeat visits.Energy Balance Prescription Energy and calorie targets for run‐in periods are obtainedusing standardized, validated equations and adjusted as warranted usingenergy‐expenditure and body‐composition data.We will use the DXA and REE metabolic cart data for the NIDDK BodyWeight Planner(Advanced and Expert Modes) to guide weight stability targets during the two run inperiods.Weight stabilization is intended to minimize variability in REE and substrate oxidationmeasures arising from acute changes in energy balance, thereby improving interpretationof calorimeter‐derived outcomes.Questionnaires The following standardized instruments are administered at screening tocharacterize phenotype as well as identify covariates and exclusionary conditions duringbaseline and testing.Instrument Construct / Rationale Items/Time Cut‐points Action / Exclusion Flags TimePoints PROMIS Global Health (10) Overall health status; anchor for between‐visitvariability 10 items / 2‐3 min T‐score < 40 Flag for covariate; consider deferring visitif acutely ill Screening PSQI Sleep quality (past month); impacts EE/RQ and adherence 19items / 5‐7 min Global score > 5 Flag; adjust scheduling or analyze as covariateScreening PSS‐10 Perceived stress; perturbs appetite/sleep/EE 10 items / 2‐3 min Score ≥20 (moderate‐high) Flag; consider deferring if acute stressor; covariate ScreeningIPAQ‐Short Habitual physical activity; context for free‐living PA vs calorimeter 7 items/ 3‐5 min <600 MET·min/wk = Low; ≥3000 = High Use category as covariate; verify extremesScreening Raid‐FN (Ro/Allison/Indiana/Dhurandhar Food Noise Inventory, short form) "Foodnoise" ‐ preoccupation, persistence, and dysphoria of food‐related thoughts; context forinterpreting postprandial craving/intake response 23 items / 2‐3 min No establishedclinical cut‐point; scored continuously Flag; reinforce standardized meal instructionsAll FCQ‐Trait (Food Cravings Questionnaire‐Trait) Trait‐level frequency/intensity of foodcravings; covariate for reward‐driven eating and meal compliance 15 items / 3‐5 min Score≥ 50 → clinically relevant trait craving (validated food‐addiction screening threshold)Flag; reinforce standardized meal instructions All AUDIT‐C Alcohol use; affectssleep/metabolism 3 items / <2 min ≥3 (women) / ≥4 (men) Counsel reduction pre‐visit;consider exclusion if heavy use Screening Caffeine Checklist Caffeine dose & timing;shifts EE/RQ & sleep 5‐6 items / <2 min >400 mg/day or intake after 12:00 Instructtaper/timing; reschedule if noncompliant Screening ESS (Epworth Sleepiness Scale) Daytimesleepiness; correlate with nocturnal EE 8 items / <2 min Score ≥ 10 Flag; consider OSAworkup; covariate Screening Menstrual Cycle History (brief) Cycle phase/regularity;hormones/HRT; key covariate for EE/RQ 6‐10 items / 2‐3 min Irregular cycles; CHC/HRT useRecord phase; schedule consistently; covariate Screening Gastrointestinal Severity RatingScale Lactose/FODMAP/spice triggers; avoid protocol‐related GI confounds 8‐12 items / 2‐3min Any major intolerance reported Adjust standardized meals; document All PHQ‐9Depressive symptoms; context for sleep/appetite changes 9 (or 8) items / 2‐3 min Score ≥10; item 9 > 0 Provide resources; may defer if unstable Screening GAD‐7 Anxiety symptoms;stress‐related metabolic variance 7 items / 2‐3 min Score ≥ 10 Provide resources;covariate Screening Berlin Obstructive sleep apnea 10 items / 5‐10 min 2+ positive scoresout of 3 categories Flag; consider OSA workup; covariate ScreeningBluetooth Scale and Healthie Provision and Orientation:At the in‐person screening visit, following completion of informed consent, study staffissue each participant a study‐owned Bluetooth‐enabled digital scale (precision ±0.1 kg)that has been verified against a laboratory reference standard prior to distribution.Staff pair the device on the participant's Healthie account on‐site and confirm asuccessful transmission before the participant leaves the visit. Participants areoriented to the daily self‐weighing procedure. Weight is taken under standardizedconditions, immediately after waking, post‐voiding, before food or fluid intake, wearingminimal clothing (same thing each time), throughout the 14‐day run‐in periods. Weightstability is defined as (1) total change < 1.0 kg across 14 days; (2) day‐to‐day change ≤100 g during days 11‐14; and (3) slope of log‐transformed weights < ±0.5 kg/week.Participants who do not meet all predefined weight‐stability criteria after 14 days maycomplete an additional two‐week stabilization period with enhanced dietary support.Participants unable to achieve stability within four weeks will be withdraw beforecalorimeter admission. For the 72 hours before each calorimeter visit, participantsfollow a polyphenol‐light diet (avoiding berries, grapes, tea, cocoa, red wine, juices,and high‐polyphenol spices) to minimize background polyphenol exposure.Healthie is a secure, HIPAA‐compliant electronic health record (EHR) and telehealthplatform designed for use by healthcare and wellness providers to support patient care,data collection, and communication. The platform integrates multiple functions, includingappointment scheduling, secure messaging, clinical documentation, and patient engagementtools, within a single system. Participants will access Healthie through a mobileapplication or web‐based portal to record study‐related information, including daily bodyweight, dietary intake, physical activity, and sleep logs. The platform also allowsparticipants to complete questionnaires and communicate with study staff as needed. Dataentered by participants are stored within a secure, encrypted environment and areaccessible only to authorized study personnel. Healthie supports real‐time data sharingbetween participants and study staff and will integrate with the study provided bluetooth scale to capture health‐related metrics. The platform complies with HIPAA privacyand security standards, including data encryption and secure data transmission, to ensurethe confidentiality and protection of participant information.Habitual Dietary Intake (ASA24) Habitual dietary intake is assessed using the AutomatedSelf‐Administered 24‐Hour Dietary Recall (ASA24®, National Cancer Institute). Thisvalidated web‐based platform guides participants through a multiple‐pass 24‐h recallusing standardized food probes, portion‐size images, and linked nutrient databases.Participants complete recalls on non‐consecutive days, including at least one weekendday. Built‐in consistency checks minimize under‐ and over‐reporting, and automatedprompts capture frequently forgotten items. Data output includes total energy intake,macronutrient distribution, micronutrient content, and timing of eating occasions,enabling harmonization with calorimetry‐derived measures.Sleep and Physical Activity Diary During run‐in and washout periods, participantscomplete a standardized daily physical activity and sleep diary documenting exercisebouts, occupational activity, sedentary behavior, and sleep‐wake timing, using structuredtime blocks with categorical activity codes, intensity ratings, and duration. Entries arecross‐validated against accelerometry and calorimeter motion sensors when available.Diaries are collected electronically through REDCap, with submissions time‐stamped toenhance compliance monitoring; completeness is reviewed weekly by study staff.Accelerometry Sleep and activity will be assessed throughout each run‐in and study periodusing wrist actigraphy (ActiGraph GT3X+, Pensacola, FL). Raw data from the device(acceleration and ambient light) will be scored using validated algorithms in theActiLife software for estimation of sleep and different levels of physical activity aswell as inactivity. ActiLife is a secure, HIPAA compliant platform; the ActiGraph devicesdo not have Bluetooth enabled or geolocation capabilities. Information from daily sleepdiaries will be used to enhance the accuracy of bed and waketime estimates derived fromscoring algorithms applied in ActiLife. Neither raw nor scored data will be stored onActiLife.Home Weight Scale Participants are provided a study‐issued smart scale (precision ±0.1kg) verified against a laboratory reference standard prior to distribution. Participantsweigh once daily under standardized conditions (after waking, post‐void, prior to food orfluid intake, minimal clothing, same time each day). Weights transmit automatically to asecure study database (Healthie platform) for monitoring by the study dietitian.Timestamped uploads monitor compliance, and outliers (±3 SD from rolling average) areflagged for verification. These data ensure weight stability prior to calorimeter entryover the 14‐day run‐in. In cases of device malfunction, participants notify study staffimmediately and a replacement scale is provided; all deviations and imputed values aredocumented.In Person Procedures:Standardized Meals ‐ Standardized run‐in and calorimeter day 0 meals: 30% fat / 55% carbohydrate / 15%protein. ‐ Mini‐meals meals: 30% fat / 55% carbohydrate / 15% protein. ‐ High‐fat test meal: Approximately 12 kcal/kg fat‐free mass (maximum 1000 kcal),containing 07:55) andpostprandial (Day 1, 21:30, 3 h after the high‐fat meal) ‐ at 36 mL each (72 mL perstay; 144 mL per participant across both stays), drawn from an antecubital vein by atrained phlebotomist or nurse. Each draw consists of: four 4 mL CPT tubes (16 mL) forStream A PBMC culture; and four 4 mL tubes (16 mL) for Stream B mitochondrialrespirometry. PBMCs are isolated by standard density‐gradient centrifugation andprocessed for high‐resolution mitochondrial respirometry (Oroboros O2k) to assessfatty‐acid‐supported respiration and spare respiratory capacity. Plasma is retained foracylcarnitine profiling. Samples are labeled with a unique study code and stored at ‐80°C in the restricted‐access Metabolism Core Lab (Webb 337). Remaining biospecimens arebiobanked for future hypothesis‐driven analyses contingent on additional funding.Postprandial blood draw timing rationale: The postprandial draw is anchored to thehigh‐fat test meal ( 3 h post‐meal), not to grape/placebo powder administration, becausethe study's primary interest is whether grape polyphenols alter the metabolic flexibility(MetFlex) response to the meal itself, not polyphenol pharmacokinetics per se. Ameal‐anchored 10‐15 min); resting energy expenditure via metabolic cart.The participant then re‐enters the calorimeter, where 24‐hour urine collection andaccelerometry begin, a fasting blood draw ( 07:55) is obtained, a standardized breakfastis provided, the grape or placebo powder (72 g) is administered 30 minutes before thehigh‐fat test meal, and a postprandial blood draw ( 21:30) is obtained 3 hours after themeal. The RAID‐FN and General Food Cravings Questionnaire‐Trait are completed. Lights andscreens are turned off at approximately 10 PM; sleeping RER and energy expenditure aremeasured overnight. The intervention product will be provided in pre‐weighed packets andreconstituted with water immediately before administration. Participants will consume theentire dose before the high‐fat test meal.Day 2: Following a 6:15 AM wake‐up call, participants remain still for a resting energyexpenditure measurement, after which the 24‐hour urine collection ends and they exit thecalorimeter.Calorimeter Activity Timing Grid Times are approximate and depend on the start time oflaboratory procedures; minor variations are acceptable.Table 2:Day Time Activity Biospecimen / Notes 0 1730 Participant enters calorimeter (VO₂/VCO₂sampled at 1‐min intervals; continuous activity monitoring) ‐ 0 1800 Measure starts;standardized evening meal (consumed within 30 min) ‐ 0 2200 Prepare for bed ‐ 0 2230Lights off; no screens (overnight sleep RER) ‐1 0630 Wake; exit calorimeter for DXA and cart REE ‐1 0755 Re‐enter calorimeter Fasting blood draw ( 40 mL); start 24‐h urine1 0800 Measure starts; standardized breakfast (within 30 min) ‐1 1200 Standardized lunch ‐1 1800 Grape or placebo powder (72 g) ‐1 1830 High‐fat test meal (within 30 min) ‐1 2130 Postprandial sampling ( 3 h after meal) Postprandial blood draw ( 65% fat / 25% carbohydrate / 10% protein. ‐ Grape or placebo powder (72 g) administered 30 minutes before the high‐fat testmeal.All meals are prepared to fixed energy and macronutrient specifications by the UABMetabolic Kitchen and consumed within a standardized ingestion window under observation.No outside food is allowed. Water intake is ad libitum but recorded; caffeine and alcoholare prohibited during calorimeter periods. For the calorimeter stays, energy balance willbe determined via the Lam equation; calorie prescription will allow for additionalcalories to be added in order to maintain energy balance within 100 calories.Participants will be fed the energy balance prescription via the Metabolic Kitchenprovided meals described above; titration will happen at the 7 hour mark to allow for thehigh caloric content of the MetFlex meal.Whole‐Room Indirect Calorimetry Whole‐room indirect calorimetry enables continuous,high‐resolution quantification of human energy expenditure and substrate oxidation withina controlled metabolic environment. The system operates as an open‐circuit indirectcalorimeter in which ambient air is drawn into the calorimeter at a precisely regulatedflow rate, typically controlled by mass flow controllers with sub‐percent errortolerance. Exhaust air is continuously sampled and analyzed for fractional concentrationsof O₂ and CO₂ using paramagnetic and nondispersive infrared analyzers, with analyzerdrift corrected by periodic calibration against precision gas mixtures traceable to NISTstandards. Dynamic energy expenditure is calculated from VO₂ and VCO₂ using the Weirequation, corrected for calorimeter volume, barometric pressure, and water vapordilution. Temporal resolution of VO₂ and VCO₂ is typically 1‐2 min, allowing detection ofrapid metabolic transitions such as the thermic effect of food. Calorimeter leakintegrity is verified prior to each study using infusion tests, ensuring stoichiometricrecovery of CO₂ and O₂. Derived parameters include resting energy expenditure, 24‐hourenergy expenditure, thermic effect of food, and the respiratory exchange ratio (RER) timeseries.Prior to calorimeter stays, participants are screened for alcohol/substance use. They maynot bring in alcohol, caffeine, gum, mints, or any outside contraband that may altermetabolism. Prior to calorimeter entry, study staff inspect participants' belongings forcontraband. Electronic devices may be used during daytime hours but must be silencedduring sleep measures.Participants will follow a standardized posture and activity script throughout chambertesting. Physical activity intensity will be limited to low‐intensity movement, includingwalking within the chamber and stretching, to minimize variability in metabolic outcomes.Room Calorimeter Physical Activity Monitoring In addition to the accelerometer,spontaneous and structured activity are quantified using a multimodal approach. Infraredmotion sensors embedded in the calorimeter provide positional and movement counts, whiletri‐axial accelerometry worn by participants records activity intensity and duration.Activity counts are time‐synchronized with VO₂/VCO₂ to attribute energy expenditure tolocomotor versus non‐locomotor components.Room Calorimeter Sleep Monitoring In addition to the accelerometer, sleep is monitoredcontinuously during calorimeter stays (approximately 22:00‐06:00). Participants may notnap during the day and are given clear lights‐out and lights‐on instructions viaintercom. Participants are asked to silence cellular devices (e.g., smartwatches, TV off)and close privacy curtains to mitigate sleep disruption. Continuous overnight VO₂ andVCO₂ are used to derive sleep EE and RER.Biospecimens Two venous draws are obtained per 40‐hour stay ‐ fasting (Day 1, 3‐hour timepoint is consistent with published postprandial monocyteactivation and lipemia studies, which commonly sample in the 3‐4 hour post‐meal window tocapture peak circulating lipid exposure and monocyte/PBMC activation. Continuouswhole‐room calorimetry data separately capture the full RER trajectory (meal‐stimulatedpeak, overnight sleep nadir) per the validated MetFlex approach (McDougal et al., 2025),so the single postprandial blood draw timepoint is not relied upon to capture theRER‐based MetFlex outcome itself.Method validation note: The PBMC isolation and high‐resolution respirometry (OroborosO2k) workflow is undergoing internal method validation (comparing CPT‐tube versusEDTA/density‐gradient separation for cell yield, viability, and compatibility with O2kchamber volume) prior to full‐scale sample processing. Validated,standard‐operating‐procedure‐documented methods will be used for all study specimens oncefinalized.Urine Twenty‐four‐hour urine collections are obtained from a urine collection deviceplaced in the in‐calorimeter restroom. Privacy curtains are closed at every void.Participants void into pre‐weighed, acid‐washed, opaque collection containers; containersare pre‐treated with boric acid (10 g/L) to stabilize pH and maintained at 4 °Cthroughout collection. Total volume is recorded gravimetrically, and completeness isverified by creatinine excretion normalized to body mass. Nitrogen excretion isquantified by elemental combustion methods, enabling calculation of protein oxidationrates when combined with indirect calorimetry data and improving the accuracy ofsubstrate oxidation partitioning (non‐protein RER adjustment).Calorimeter Day‐by‐Day Procedures (40‐hour stay) Arrival (Day 0, evening): Participantsarrive at the Webb Calorimetry Facility the evening before the full calorimeter day.Diaries and weights are reviewed for completeness. A standardized evening meal isprovided, and participants sleep in the calorimeter overnight so that sleeping RER andenergy expenditure can be measured.Day 1 (full calorimeter day): Following a wakeup call: height/weight assessment; DXA scan(fat mass and fat‐free mass, 40 mL) 1. 2230 Lights off; no screens (overnight sleep RER) ‐ 2. 0615 Wake; void; sip water ‐2 0630‐0700 Resting energy expenditure measure ‐ 2 0705 Exit calorimeter End 24‐h urinecollection Biospecimens Peripheral blood mononuclear cells (PBMCs) will be isolated from32 mL of venous whole blood collected at the specified time points during the chamberprotocol (See Table 2). Baseline and post ingestive PBMCs will be isolated using standarddensity‐gradient centrifugation methods. Isolated cells will be cryopreserved in multiplesub‐aliquots and stored in liquid nitrogen to support downstream mitochondrialrespiration assays and exploratory molecular analyses.Twenty‐four‐hour urine collections will be obtained during chamber stays using acollection device located within the in‐chamber restroom. Participant privacy will bemaintained using privacy curtains during all voids. Total urine volume will be recordedgravimetrically, and completeness of collection will be verified using creatinineexcretion normalized to body mass.Urinary nitrogen excretion will be quantified using chemiluminescence or elementalcombustion‐based methods (e.g., Kjeldahl), enabling estimation of protein oxidation rateswhen integrated with indirect calorimetry data. Incorporation of urinary nitrogen withVO₂ and VCO₂ measurements will allow adjustment for non‐protein respiratory exchangeratio (RQ), thereby improving the accuracy of whole‐body substrate oxidationpartitioning. This biospecimen strategy enables mechanistic assessment of mitochondrialbioenergetics that can be directly aligned with whole‐body metabolic outcomes, whilepreserving sample integrity for future analyses. Primary cellular outcomes will includefatty‐acid‐supported mitochondrial respiration and spare respiratory capacity measured byhigh‐resolution respirometry in cryopreserved PBMCs. These phenotypes were selected fortheir robustness to cryopreservation, biological interpretability, and relevance to lipidoxidation during a high‐fat challenge. Exploratory respirometric parameters will beanalyzed to generate mechanistic hypotheses and inform future study design. PBMCmitochondrial phenotypes will be evaluated as secondary mechanistic endpoints tocontextualize changes in sleep and postprandial respiratory exchange ratio. Remainingbiospecimens will be biobanked for future hypothesis‐driven analyses contingent onadditional funding.Washout and Crossover After the first calorimeter stay, participants resume a eucaloricdiet, avoid polyphenol‐containing supplements, and maintain weight stability (±1.0 kg)during washout. The 14‐day weight‐stabilization run‐in, polyphenol‐light diet, andcalorimeter procedures are then repeated for the second visit with the alternate powder.After the first calorimeter stay, participants resume a eucaloric diet, avoidpolyphenol‐containing supplements, and maintain weight stability (±1.0 kg) duringwashout. During the 72 hours preceding the crossover visit, participants repeat thepolyphenol‐light diet. The 14‐day weight stabilization run‐in and all calorimeterprocedures are repeated before the second chamber stay with the alternate intervention.Sampling Methods Convenience sampling is used to recruit eligible lean adults and adultswith overweight/obesity meeting inclusion criteria from the UAB/Birmingham catchmentarea.Sample Size Calculation The sample size is based on detecting a clinically meaningfulabsolute difference in postprandial RER (ΔRER = 0.02) between grape and placeboconditions in a 2‐period crossover. Assuming a within‐person SD of approximately 0.03, α= 0.05, and 80% power, 18 completers are required; the study enrolls 20 to allow forattrition.