The findings of previous experiments suggested that alpha linolenic acid (ALA) has been linked to anti-hyperglycemic, and reducing the risk of diabetes.This is a randomized double-blind cross-over trial, aims to study the effect of ALA on glycemic status and human metabolism. Firstly, the investigators will investigate the efficacy of ALA on improving the indexes of glucose metabolism. Secondly, next generation sequencing (NGS), ultra-high performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) and gas chromatography-mass spectrometry detection will be conducted to explore the role of ALA on gut microbiota as well as metabolites. Thirdly, single nucleotide polymorphism will be genotyped by Time-of-flight mass spectrometry to find the gene-environment interaction effect.

Inclusion Criteria:

• Fasting blood glucose 6.1-8.4mmol /L;
• HbA1c 5.7-7.0%;
• Patients with previously diagnosed type 2 diabetes with stable drug hypoglycemic treatment and blood glucose controlled well.

Exclusion Criteria:

• Under 30 years old or over 75 years old;
• Suffering from severe metabolic disorders, malignancies, psychiatric conditions;
• undergoing insulin therapy, or antibiotic/probiotic use for more than three consecutive days in the last month.
• Daily cooking oil is flaxseed oil, rapeseed oil or other α -linolenic acid rich vegetable oil;
• Intake more than 20g walnuts per day or more than 100g fatty fish per week in the last month;
• Take nutritional supplements, such as fish oil capsules, perilla seed oil and flaxseed oil capsules, for nearly one month;
• Allergic to the content of intervention;
• Failure to eat the tested sample as prescribed and affect the efficacy or safety judgment.