The study aims to study healthy men aged 18-40 to explore how different beverages affect hunger, blood sugar, insulin, and a hormone called GLP-1, which helps regulate appetite and blood sugar. The tested beverages include two prebiotic sodas (Olipop and Poppi), Diet Coke, and Coca-Cola Classic.

What's the study about? It aims to understand how these drinks influence how full participants feel and how the body handles sugar and hormones compared to each other. This could help us learn more about how prebiotic drinks, which may support gut health, compare to regular sugary or diet sodas.

What will participants do?

Participants will visit our lab at TCU (Rickel Building, rooms 256/259) four times over four weeks, with each visit lasting about 2-2.5 hours. Participants will need to fast for 8-12 hours before each visit. Here's what happens:

• First visit involves participants' consent, measurement of height and weight, and performing a finger-stick test to check blood sugar and HbA1C. Participants will also fill out questionnaires about health, diet, and beverage preferences.
• Visits 2-4: In visit 2, a DEXA scan will be performed to assess body composition. In visits 2-4, participants will drink one of the four beverages (in a random order, served in an unlabeled black container to prevent drink identification). Other variables measured at these time points include blood pressure, fasting glucose, insulin, and GLP-1. Participants will also complete questionnaires about hunger and how the drink tastes.

Each visit is spaced out by a week, and the total time commitment is about 10.5 hours. The study is expected to complete participant recruitment by December 10, 2025.

Who can join? Ten healthy men aged 18-40 who don't have diabetes, heart disease, kidney or liver issues, or other specific health conditions. Participants shouldn't smoke, vape, or have certain dietary habits like intermittent fasting. Participants will be screened to confirm eligibility.

What are the risks? The risks are low but include discomfort from blood draws or the IV catheter, a small chance of infection, and minimal radiation exposure from the DEXA scan (similar to everyday background radiation). There's also a small risk of a data breach, but participant information will be secured with password-protected systems and use ID numbers instead of names.

What do participants get? Participants will receive a DEXA scan, baseline blood sugar, and HbA1C tests. If participants have abnormal results (like high blood sugar), doctor visits would be recommended. There are no direct benefits to participants, but participation could help develop better dietary recommendations in the future.

How is privacy protected? Data will be stored securely on password-protected computers and in locked lab facilities, following HIPAA rules. Blood samples will be frozen for up to 10 years for possible future research (with participants' consent) and labeled with an ID number, not participants' names.

How to join? Participants will be recruited through flyers, emails, social media, and TCU classes. If interested, participants will complete an online screening form or scan a QR code on our flyer. If eligible, participants will be contacted to confirm details and explain the study further.

If participants have questions or want to join, contact Dr. Elisa Marroquin at e.marroquin@tcu.edu or Matthew Loritz at m.loritz@tcu.edu. Participation is voluntary, and participants can withdraw at any time, though data will be kept for analysis.

Study Overview This research study, conducted by the Texas Christian University (TCU) Department of Nutritional Sciences and Kinesiology, aims to investigate the effects of carbonated prebiotic beverages (Olipop and Poppi) compared to caloric (Coca-Cola Original) and non-caloric (Diet Coke) beverages on satiety, blood glucose, insulin, and glucagon-like peptide-1 (GLP-1) responses in healthy male participants aged 18-40. The study is a single-blind, randomized crossover trial designed to explore how these beverages influence metabolic and appetite-related outcomes, addressing gaps in understanding the physiological impacts of functional beverages containing prebiotics versus widely consumed caloric and non-caloric alternatives.

Objectives and Hypotheses The primary objective is to evaluate the acute effects of four beverages-Olipop, Poppi, Diet Coke, and Coca-Cola Classic-on satiety, plasma glucose, insulin, and GLP-1 levels. Secondary objectives include assessing body composition and beverage palatability and gastrointestinal (GI) symptoms. The hypothesis is that prebiotic beverages will enhance satiety and GLP-1 secretion due to fiber content, potentially via gut microbiota fermentation, without significantly increasing glucose or insulin levels compared to Coca-Cola. Diet Coke may elicit a modest GLP-1 and satiety response due to artificial sweeteners, but minimal glucose/insulin changes. Coca-Cola is expected to cause significant glucose and insulin spikes due to its high sugar content. Additionally, hunger is expected to be reduced across all conditions, with prebiotic beverages potentially showing superior satiety effects.

Study Design

• Type: Prospective, interventional, single-blind, randomized crossover trial.
• Participants: 10 healthy males aged 18-40, accounting for a 30% attrition rate.
• Duration: Four visits, each 2-2.5 hours, separated by a one-week washout period (total ~10.5 hours).
• Randomization and Blinding: Each participant consumes all four beverages in random order, served in unlabeled black containers to minimize bias.
• Data Collection: Anthropometric measurements, body composition (DEXA scan), biochemical markers (glucose, insulin, GLP-1), and survey data (satiety, GI symptoms, beverage preference) are collected.

Study Procedures

1. Screening and Visit 1:

   • Informed consent is obtained, followed by measurement of height, weight, and blood pressure.
   • A finger-stick test assesses fasting blood glucose and HbA1c.
   • Participants complete demographic, health, beverage preference, and 3-day food log questionnaires.

2. Visits 2-4:

   • A DEXA scan measures body composition (visit 2 only).
   • Participants fast for 8-12 hours before each visit.
   • Blood pressure is measured, and fasting status is confirmed via finger-stick.
   • An intravenous catheter is inserted for blood sampling at 0, 15, 30, 60, 90, and 120 minutes post-beverage consumption to measure glucose, insulin, and GLP-1.
   • Participants consume one beverage (355 mL) within 5 minutes.
   • Satiety Questionnaires are completed at baseline and specific intervals.
   • GI Symptomps Questionnaire are filled out 24h after each visit.
   • Beverage Rating QUesitonnaire will be applied at the end of each visit.
   • Total blood volume per visit is approximately 30 mL.

Beverages Tested

• Olipop and Poppi: Prebiotic sodas containing inulin and other fibers, low calories (~20-35 kcal).
• Diet Coke: Non-caloric, sweetened with aspartame (46 mg).
• Coca-Cola Original: Caloric (140 kcal, 39 g of sugar).

Recruitment and Screening

• Methods: Flyers, emails, social media, and in-person recruitment in TCU classes.
• Process: Potential participants complete an online screening form by following the QR code from the flyers and emails. Eligible candidates undergo phone screening to confirm inclusion/exclusion criteria and receive a study overview.

Data Collection and Analysis

- Anthropometric, body composition, biochemical, and survey data will be collected as indicated in Outcome Measures.

Risks and Mitigation

1. Blood Draw/IV Catheter: Low risk of discomfort, bruising, or infection; mitigated by trained personnel and sterile techniques.
2. DEXA Scan: Minimal radiation exposure (~0.1 mSv, equivalent to background radiation); limited to one scan.
3. Data Breach: Risk minimized by deidentification, secure storage, and restricted access to IRB-approved personnel.
4. GI Discomfort: Possible with prebiotic beverages; monitored via GI Symptoms Questionnaire.

Benefits

• Direct: Participants receive a $150 gift card, DEXA scan results, baseline glucose, and HbA1c levels (finger sticks)
• Indirect: No direct benefits, but results may inform evidence-based recommendations for beverage consumption.

Results Sharing

• Baseline finger-stick results (glucose, HbA1c, lipids) are shared at testing.
• Lab-measured glucose and insulin levels, analyzed in batches after all participants complete the study, will not be shared, as delayed analysis limits immediate clinical utility.

Inclusion Criteria:

• Gender: Male
• Age: 18-40 years
• Health Status: Healthy, with no significant medical conditions
• Body Mass Index (BMI): 18.5-24.9 kg/m²

Exclusion Criteria

• Diabetes: Diagnosed diabetes (Type 1 or Type 2)
• Gastrointestinal Disorders: Any diagnosed gastrointestinal conditions (e.g., irritable bowel syndrome, inflammatory bowel disease)
• Liver Disease: Any diagnosed liver conditions
• Kidney Disease: Any diagnosed kidney conditions
• Cardiovascular Disease: Any diagnosed cardiovascular conditions
• Hypertension: Diagnosed high blood pressure
• Recent Illness or Infection: Any illness or infection within the past 30 days that could affect study outcomes
• Tobacco or Nicotine Use: Current use of tobacco or nicotine products (e.g., smoking, vaping)
• Phenylketonuria (PKU): A genetic disorder affecting phenylalanine metabolism, due to the presence of aspartame in Diet Coke
• Medication Use: Use of medications or supplements that affect glucose metabolism, insulin response, or appetite
• Intermittent Fasting: Engagement in intermittent fasting or inconsistent time-restricted feeding patterns
• Other Health Conditions: Any other health conditions that, in the opinion of the investigators, could interfere with study participation or outcomes

Biological males only

Additional analyses may be conducted on our data following the conclusion of this study. However, if the study and the analyses described herein are completed and no further analyses are planned by our research team, the data may be made available upon request by contacting Elisa Marroquín