<qa>  How many participants will be enrolled in this study?Approximately 22 participants will be enrolled in this study at the Chronic Viral Illness Service of the McGill University Health Centre, the Ottawa Hospital and the Maple Leaf Medical Clinic Toronto. This study will last about 24 weeks; metformin treatment will be for 12 weeks. In order to be eligible for the study, the participants must be 18 years of age or older, have an undetectable viral load the quantity of the HIV virus in the blood must be less than 50 copiesml for at least 3 months and have a CD4CD8 ratio of less than 0.7. All participants will also be asked to give blood and stool samples and optional colon mucosal biopsy samples before and after metformin supplementation to study the size of the viral reservoir and the amount of T cell activation and changes in gut microbiota composition. 