The aim of this study is to evaluate the effect of precision nutrition education using continuous glucose monitoring system (CGMS) in longterm glycemic control in patients with type 2 diabetes mellitus. Glucose levels in subjects who received diet education using CGMS will be compared to those in subjects who received conventional diet education.

Fifty subjects with type 2 diabetes will be recruited. Every subject will be randomized in two groups, which are CGMS education group and conventional education group. The study will be conducted for 12 weeks for each participants. Intervention group will receive diet education based on CGMS data, using post prandial glucose response, calculated by incremental area under curve of glucose level. Control group will receive conventional diabetes diet education without CGMS data. Primary outcome is change of HbA1c from baseline for 12 weeks, and secondary outcomes are changes of fasting blood glucose level, body weight, waist circumference, blood lipid level, homeostatic model assessment of insulin resistance (HOMA-IR) , c-peptide, microbiome, 7-point self monitoring of blood glucose (SMBG), and compliance/satisfaction questionnaire from baseline for 12 weeks.

Inclusion Criteria:

• Type 2 diabetes patients (Fasting blood glucose ≥ 126 mg/dl or HbA1c ≥ 6.5% or Subjects who were previously diagnosed with type 2 diabetes and who have been treated with lifestyle modification only, oral anti-diabetic drugs or basal insulin)
• HbA1c 6.5%~10%
• Body weight change less than 5% in 3 month
• Subjects who agreed to the study protocol

Exclusion Criteria:

• Type 1 diabetes patients
• Subjects using insulin other than basal insulin
• Subjects who have newly started or have changed anti diabetic drugs within 3 months
• Subjects who have been received diabetes diet education within 6 months
• Females who are pregnant or doing breast feeding
• Subjects with alcohol addiction or drug abuse
• Subjects who are using drugs that can influence blood glucose levels (e.g. steroid)
• Subjects who are currently using acetaminophen or who should use acetaminophen during CGMS attach period
• Subjects who have skin problems on CGMS sensor insertion site (e.g. burn, excessive body hair, inflammation, rash, tattoo)
• Subjects who have newly started, changed, or stoped probiotics or prebiotics within 2 weeks
• Subjects who have used antibiotics (oral or intravenous) within 2 weeks
• In addition, if it falls under the exclusion criteria according to researchers discretion