Effect of Standardized Large Yellow Tea Extract on Triglyceride Response After a High-Fat Meal in Healthy Adults

The study will enroll healthy adults aged 18 to 45 years who meet predefined clinical and laboratory eligibility criteria. Participants will be randomized in a 1:1 ratio to one of two crossover sequences: Tea-Water (TW) or Water-Tea (WT). Each participant will therefore receive both interventions during the study.

In the tea intervention period, participants will consume a single dose of 3 g of standardized large yellow tea extract dissolved in 250 mL of warm water. In the control period, participants will consume 250 mL of warm water. Both interventions will be administered immediately after completion of a standardized high-fat meal. The two intervention periods will be separated by a washout period of at least 7 days.

On each study day, participants will arrive after an overnight fast. A baseline blood sample will be collected before consumption of the standardized high-fat meal. The meal will be completed within 20 minutes, followed immediately by the assigned study beverage, which will be consumed within 10 minutes. Additional blood samples will be collected at 0.5, 1, 1.5, 2, 4, and 6 hours after the meal.

The primary outcome is the 0- to 6-hour incremental area under the curve for plasma triglycerides. Secondary outcomes include postprandial triglyceride kinetics, triglyceride peak concentration and time to peak, and selected lipid-related measures. Exploratory analyses will assess additional metabolic measures and plasma and urine metabolomic profiles to identify potential exposure biomarkers and metabolic pathways associated with the triglyceride response.

Although the study is open-label to participants and study staff, biological samples will be coded, and laboratory personnel and statistical analysts will remain blinded to treatment assignment when feasible. Safety and tolerability will be assessed through adverse-event monitoring, vital signs, and relevant laboratory assessments.

Inclusion criteria

• Voluntary participation in the study, with full understanding of the study objectives, procedures, and potential risks, and provision of written informed consent.
• Healthy adults aged 18 to 45 years, male or female.
• Body mass index (BMI) of 18.5 to 24.0 kg/m², with relatively stable body weight (change <5% during the previous 3 months).
• Generally normal physical examination and vital signs, including:

• Systolic blood pressure: 90-139 mmHg;
• Diastolic blood pressure: 60-89 mmHg;
• Resting heart rate: 50-100 beats/min;
• No clinically significant abnormal physical findings.
• Baseline laboratory results meeting the following criteria:

• Complete blood count within the reference range, or minor deviations considered clinically insignificant by the investigator;
• ALT, AST, ALP, GGT, and total bilirubin within the upper limit of normal (ULN), or no more than 1.2 × ULN and considered clinically insignificant by the investigator;
• Serum creatinine and blood urea nitrogen within the reference range and estimated glomerular filtration rate (eGFR) ≥90 mL/min/1.73 m²;
• Fasting plasma glucose approximately 3.9-6.1 mmol/L, without a diagnosis of diabetes or prediabetes;
• Triglycerides <2.3 mmol/L and LDL-C <4.1 mmol/L, or according to the reference ranges of the local laboratory and investigator judgment.
• No history of serious cardiovascular, hepatic, renal, gastrointestinal, respiratory, neurological, hematological, endocrine, or other major systemic disease, or only mild chronic conditions considered by the investigator not to substantially affect study safety or outcomes.
• No known allergy to tea or its components, including tea polyphenols or caffeine, and no history of serious adverse reactions after tea or caffeine-containing beverages.
• No regular use during the previous month of lipid-lowering drugs, glucose-lowering drugs, antihypertensive drugs, glucocorticoids, high-dose antioxidant supplements, weight-loss products, or other medications or supplements that may affect glucose or lipid metabolism or pharmacokinetic outcomes.
• Moderate intake of tea, coffee, and other caffeine-containing beverages during the previous week, and willingness to restrict other tea and caffeine-containing beverages from 3 days before the study until completion of the study.
• No alcohol abuse or drug abuse.
• Ability and willingness to comply with all study procedures, including scheduled visits, blood and urine sampling, and recording of medications and adverse events.

Exclusion criteria

• Known or suspected allergy to tea, tea polyphenols, caffeine, theanine, or any component of the study product, or a history of severe allergic reactions.
• History or current presence of clinically important cardiovascular, hepatic, renal, gastrointestinal, endocrine/metabolic, neurological, psychiatric, or other systemic disease that, in the investigator's judgment, may affect participant safety or study outcomes.
• Any history of malignant tumor or current treatment for malignancy.
• Clinically significant baseline laboratory abnormalities, including but not limited to:

• ALT or AST >1.5 × ULN;
• Total bilirubin >1.5 × ULN;
• Serum creatinine above the upper limit of normal or eGFR <90 mL/min/1.73 m²;
• Clinically significant abnormalities in complete blood count;
• Fasting plasma glucose ≥6.1 mmol/L or HbA1c ≥6.5%.
• Use within the previous 3 months of lipid-lowering drugs, glucose-lowering drugs, long-term systemic glucocorticoids, anticoagulants, antiarrhythmic drugs, or strong enzyme-inducing or transporter-modifying drugs that may interfere with study outcomes.
• Regular use within the previous month of high-dose antioxidants, dietary supplements, herbal preparations, green tea extract, grape seed extract, ginseng, Ganoderma lucidum, or other lipid- or glucose-modifying supplements considered likely to interfere with the study.
• Participation in another clinical trial or healthy-volunteer study within the previous 3 months, receipt of an investigational drug or device, or blood donation/blood loss ≥400 mL within the previous 3 months.
• Alcohol or drug abuse, or marked caffeine sensitivity causing symptoms such as palpitations, insomnia, tremor, or anxiety after small amounts of coffee, strong tea, or other caffeine-containing beverages.
• Pregnancy, breastfeeding, planned pregnancy within the next 3 months, or refusal by women of childbearing potential to use reliable contraception during the study.
• Significant circadian rhythm disturbance, long-term night-shift or rotating-shift work, severely irregular sleep, or anticipated travel/work scheduling likely to interfere with study visits or sampling.
• Any condition considered by the investigator likely to result in poor compliance or inability to complete study procedures.
• Any other condition that, in the investigator's judgment, makes the individual unsuitable for participation.