This is a dietary intervention study, which aims to explore different diet challenges for glucose metabolism, including carbohydrates and intermittent fasting (IF) dietary pattern. Considering the glucose responses to the same food are largely heterogeneous among people, this study integrates the concepts of precision nutrition and N-of-1 design. The study also aims to explore differences in brain structure and function between participants with different Body Mass Index (BMI) from the perspective of gut-brain axis.

This study aims for precision nutrition. Participants will be required to wear continuous glucose monitoring (CGM) for 14 days. The diet intervention will be carried out after wearing CGM on Day 1. Individual N-of-1 trial design will be employed during Day 2 to Day 7 to compare the difference of postprandial glucose response to white bread or plain oats. These two breakfasts will appear in alternating order every successive 2 days, and these successive 2 days will be defined as one set. There will be 3 sets during Day 2 to Day 7. Between lunch and dinner will be the wash out period for the remaining effect of the last breakfast intervention on blood glucose homeostasis. In this period, participants will be allowed to choose foods without restrictions, but dietary records are required. The period during Day 8 to Day 14 is defined as intermittent fasting (IF) period, and participants will experience moderate fasting on Day 9 and Day 13 with total energy intake restrained within 500-600 kcal. In these two fasting days, participants will be provided with daily three meals. Investigators will closely monitor participants' latent adverse response and compliance to ensure the intervention will be completed with adequate safety and high compliancy. Oral glucose tolerance test (OGTT) will be conducted in the morning of Day 8 and Day 14 to test the changes of glucose tolerance before and after one set of IF intervention. Electroencephalogram (EEG) and functional Magnetic Resonance Imaging (fMRI) scanning will be conducted as per standard procedure at baseline.

Inclusion Criteria:

• Participants reside in Hangzhou
• Participants have no traveling plans within 3 months

Exclusion Criteria:

• Refusing or unable to give informed consent
• Participants with chronic gastrointestinal diseases and take daily relevant medications
• Participants with metabolic diseases including diabetes, hypertension and cardiovascular diseases (CVD)
• Participants with craniocerebral trauma, cancer, liver disease, kidney disease, or other critical illness, or history of operation or medication
• Participants with bulimia nervosa, post-traumatic stress disorder (PTSD), chronic anxiety and depression or other critical neuronal disorder or history of relevant medication
• Being or to be pregnant or lactating.
• Participants with history of alcohol or drug addiction, or smoke above 15 cigarettes per day
• Concurrently participating other clinical trials.