Food plays a crucial role in determining blood glucose levels, especially in people with type 2 diabetes. Precision nutrition, which involves individually tailored dietary interventions, can be a powerful tool in managing blood glucose levels in people with type 2 diabetes. Previous studies found that changes in gut microbiota resulted from the dietary intervention, such as plant-based diet, might subsequently lead to different glycemic responses, and then different health outcomes.

In this study, the investigators will characterize the blood glucose dynamics and gut microbiota of individuals with type 2 diabetes. They aim to assess the influence of plant-based diet on gut microbiota; they will also investigate the influence of gut microbiota on glycemic responses. Additionally, a series of individual N-of-1 trails will be integrated to compare the effects of a white bread breakfast and a whole wheat bread breakfast on glucose metabolism at the individual level.

Choice of design: The study is a two-arm intervention study integrated with N-of-1 design.

Study population: Patients with type 2 diabetes.

Screening Assessment: Prospective participants will be selected based on the pre-defined inclusion and exclusion criteria. Recruitment will be done over the phone and via the social media.

Study duration: Each participant will take part in the study for a period of up to 1 month at baseline and have follow-up visits every 1-2 years.

Dietary intervention:

The PRECISION-T2D is a dietary intervention study. Upon admission, patients will be randomly assigned to two groups: plant-based diet and conventional diabetic diet. Throughout the hospitalization, all participants (n=200) will be given standardized meals. A dietitian will design the diet for both plant-based and conventional diabetic diet groups following 2023 Chinese Diabetes Society guidelines. Both diets comprised approximately 50-65% of energy from carbohydrates, 20-30% of energy from fat, 15-20% from protein. The plant-based diet had higher fiber content (25-30g) compared to the conventional diabetic diet (15-20g). Participants will be asked to consume the entire amount of food indicated for the standardized meals and to record any leftover food. All participants will be asked to track their meals, snacks and drinks with instructions on how to record their daily dietary information. Participants will also be advised not to modify their exercise habits during the course of the study. Upon discharge, Participants in the plant-based diet arm will be recommended to consume more fiber-rich foods, including whole grains, fruits, legumes and vegetables; to moderate their intake of fish, eggs and dairy products; and to avoid other animal products. Participants in the conventional diabetic diet arm will be recommended to have a diet following 2023 Chinese Diabetes Society guidelines. Individual N-of-1 trial design will be employed to all participants during day one to day twelve to compare the difference of postprandial glucose response to white bread or whole wheat bread. These two standard breakfasts will appear in pseudo-random order. During the participants' first baseline visit day, they will be asked to complete a baseline questionnaire to collect information on their lifestyle, dietary habits, history of medications, sleep quality and appetite. Anthropometric measurements, ultrasonography evaluation, and laboratory tests will be taken using standard protocols. Participants will then be asked to wear a continuous glucose monitor (CGM) for 14-day blood glucose monitoring, which will be done by a nurse. On day 14, participants will be asked to come in for a clinical visit where they will receive their CGM report and provide blood, saliva, urine and stool samples. On day 30, participants will be asked to come in for another clinical visit where they will provide blood, saliva, urine and stool samples.

Inclusion Criteria:

• Diagnosed with type 2 diabetes;
• Living in Hangzhou for at least five years;
• Have the willingness or ability to complete the intervention and sample collection

Exclusion Criteria:

• Mental and physical disability;
• Already is a vegetarian;
• Cancer and serious complications from type 2 diabetes, such as renal failure;
• Using insulin for more than 5 years;
• Unstable medical/medication status;
• Current alcohol or drug abuse;
• Taking antibiotics in the last three months