Participants with both prediabetes and obesity who undergo physical examinations at the
Health Management Center of Nanjing First Hospital will be recruited for this study. The
details of this study design are as follows:
Inclusion and exclusion criteria for participants. Inclusion criteria are as follows: 1)
Age between 18 and 59 years old; 2) Body mass index (BMI) ≥ 28 kg/m2; 3) No consumption of
coffee in the past month; 4) Provide written informed consent; 5) Abnormal glucose tolerance,
as per the 1999 WHO diagnostic criteria for prediabetes, includes impaired fasting glucose
(IFG), impaired glucose tolerance (IGT) or a combination of both, with blood glucose
fluctuations within an abnormal range (fasting blood glucose ≥6.1 mmol/L but <7.0 mmol/L,
and/or 2-hour glucose tolerance blood glucose ≥7.8 mmol/L but <11.1 mmol/L). The exclusion
criteria for participants include individuals who 1) have been diagnosed with diabetes or are
taking anti-diabetic drugs; 2) have a history of diseases such as cancer, liver and kidney
dysfunction, existing cardiovascular and cerebrovascular diseases, and other diseases that
may affect glucose and lipid metabolism; 3) self-report gastrointestinal reaction or
intolerance to coffee and reject coffee consumption; 4) are pregnant or planning to become
pregnant in the near future; 5) are deemed unsuitable to participate in this study by
researcher believes that they are not to participate in this study.
Sample size calculation: Based on the estimation of research purpose, research design,
expected effect size, and statistical analysis method, the sample size is determined to be
100 cases, including fifty cases in the intervention group and fifty cases in the control
group.
Definition of the intervention group and placebo group: the intervention group serves as
the coffee capsule group, and will receive 3.6 g of coffee capsules per day (0.3 g/capsule, 6
capsules/time, 2 times/day, once in the morning and once in the middle of the day). The
placebo group (control group) is required to consume 3.6 g of cornstarch capsules per day
(0.3 g/capsule, 6 capsules/time, 2 times/day, once in the morning and once in the middle of
the day).
Follow-up and data collection: this follow-up period will span three months. Before and
after the 3-month intervention the participants will partake in:
regular assessments. Demographic characteristics and medical information will be
collected, including age, gender, occupation, education level, income, medication
history (hormones, contraceptives, etc.), and family history of chronic diseases.
Besides, using questionnaires, we also collect lifestyle information such as smoking,
drinking, diet intake, physical activity, and sleep of participants. Specifically, the
Simplified Food Frequency Questionnaire (FFQ25) and 24-hour Diet Record Questionnaire
(DR) are employed to assess the dietary intake of participants in the past six months
and the previous 24 hours (one day each in the middle of the week and on the weekend),
respectively. International Physical Activity Questionnaire (IPAQ) is utilized to assess
various aspects of physical activity, including time, frequency, and intensity. The
sleep information (sleep time, sleep quality, etc.) is evaluated by Pittsburgh sleep
quality index (PSQI).
A 75 g oral glucose tolerance test (75 g-OGTT). Blood samples are taken fasting and 30,
120 minutes after the glucose load. Blood samples are analyzed for glucose, insulin,
C-peptide, and glucagon.
2-week continuous glucose measurement using blinded continuous glucose monitor/sensor on
upper arm.
Fasting blood samples: glycated hemoglobin (HbA1c), total cholesterol, high-density
lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C),
triglycerides, high sensitivity C-reactive protein (CRP), interleukin 6 (IL-6).
Furthermore, blood pressure, transient hepatic elastography for the assessment of fatty
liver degree, body composition analysis, and heart rhythm variation analysis are
collected using corresponding instrument and equipment inspection. Additionally, blood,
urine, and stool samples will be collected for further analysis.