The goal of this study is to compare metabolic response to variations in dietary glycemic index in healthy participants. The main questions it aims to answer are:

• What are the metabolic hunger and food intake responses to different levels of glycemic index on the background of otherwise constant macronutrient composition? Participants will come to the lab after an overnight fast and body composition will be tested by bio-impedance analysis and magnetic resonance imaging. They will then be randomized to eat one of three standardized breakfasts varying in the glycemic index. Circulating glucose levels will be monitored using a continuous glucose monitor and blood samples will be collected to measure metabolic and hormone factors in the serum. Participants will also rate their hunger at 0, 30, 60, 120, 180, 240 and 300 minutes. After 5 hours they will eat a free choice meal from a standardized selection buffet (test meal).

The primary variable in this study is the food energy intake at the test meal consumed 5 hours after the dietary intervention meal on day1 of the experiment, compared to the intake of the same test meal consumed on day 0. The investigators performed a power analysis using this outcome measure to inform the sample size if the data were analysed using one-way ANOVA. The number of levels in the study is 3, the investigators set the effect size as a difference between means of the groups of 265 kJ. From a pilot study of repeated measurements across individuals the investigators observed the standard deviation of the difference between repeated intakes was 372 kJ. The investigators set the power value of the study at 80 %. This analysis suggested a sample of 39 individuals per group. To account for individuals potentially not completing the study, the investigators aimed to recruit 135 participants in total.

The experiment includes the pre-test, the dietary intervention and postprandial monitoring.

Pre-test. The participants will be fed a test meal (free choice from buffet) at noon the day before the experiment (day 0). The food preference and total energy intake will be assessed. On the experimental day (day 1), the participants will be asked to attend the laboratory in the morning after an overnight fast (10 hours fasting). The body composition will be measured using a bio-impedance and magnetic resonance imaging, Then the participants will be guided to wear a continuous glucose monitoring system (CGMS) and the CGMS is under initialization for 2 hours. Also, a peripheral venous catheter (PVC) will be placed in the back of the hand, upper arm or elbow socket and 6 ml of fasting peripheral blood will be drawn (0 min).

Dietary intervention. 60 male and 60 female participants will be randomly divided into three groups: low, moderate and high glycemic index groups. Each group consists of 20 males and females. They will be feed by standardized meal with constant fat, protein and carbohydrate % but differing in the source of the carbohydrates.

Postprandial test. The test includes the testing of physiological indices during and after the intervention meal. In addition to continuously recording the changes in blood glucose by CGMS, the hunger rate will be accessed at 30 minutes intervals and peripheral blood will be collected by PVC (6 ml each time) at 30, 60, 120, 180, 240 and 300 min after the meal. When the participants have finished the tests during 300 min, a test meal will be provided identical to that provided on day 0. The effect of the standard meal on the total energy intake and macronutrient (carbohydrate, protein, fat) supply will be accessed in absolute amounts and the change between day 0 and day 1.

Inclusion Criteria:

• Healthy adults (both men and women)
• 18-40 years old
• 18.5 ≤ BMI (body mass index)<24 kg/m2

Exclusion Criteria:

• Those who have undergone surgery in the past 6 months.
• People are requiring long-term medication.
• People have metabolic diseases, like diabetes, hypoglycemia, gout, osteoporosis, et al.
• Those who have recently lost weight for various medical reasons (e.g. cancer, etc.).
• People are losing weight by tablets.
• People are suffering from infectious diseases (e.g. HIV, etc.)
• People have blood phobia, pathological hypo or hyper tension.
• People with impaired glucose tolerance.
• Pregnant and lactation women.
• Those who are afflicted with claustrophobia.