Cognitive disorders increase with age and in the presence of metabolic diseases such as Type 2 Diabetes Mellitus (T2DM). In addition, digestive disorders, changes in dietary pattern and decreased activity negatively influence the microbiome. The hypothesis is that pharmacological intervention with metformin will modify the composition of the gut microbiota and cognition. The study has a pilot longitudinal design, where each patient with T2DM will be followed for one year. Two groups will be recruited: 1. Group A: The aim will be to evaluate the associations between glucose (measured by continuous glucose monitoring (CGM)), cognitive function (by means of cognitive tests and magnetic resonance imaging (MRI)), physical activity (recorded by activity and sleep tracker devicer), metformin, diet (evaluated by nutritional survey) and composition of the microbiota (evaluated by metagenomics), during 12 months (6 months without metformin and 6 months with metformin treatment). 2. Group B: The aim will be to evaluate the associations between glucose, diet (evaluated by nutritional survey), cognitive function (by means of cognitive tests), physical activity (measured by activity and sleep tracker device), the treatment and composition of the microbiota (evaluated by metagenomics), during 12 months.