Fat tissue in different parts of the body has different characteristics. Several studies have associated abdominal fat to an increased risk for multiple metabolic diseases, such as type 2 diabetes and cardiovascular disease, compared with fat located under the skin at the hips and thighs. However, the investigators do not know how the abdominal fat causes or contributes to the development of these diseases or how the development of these disease may in turn cause or contribute to changes in the fat tissue. The general objective of this study is to understand these mechanisms. To investigate these questions, the study will recruit 140 participants, both men and women aged 18-65 years. The participants will be divided into three groups: 40 people with obesity, 40 with diabetes, and 60 lean individuals. Participants will be recruited from patients at the CIUSSS du Nord-de-l'Île-de Montréal - Hôpital du Sacré-Coeur de Montréal who are awaiting bariatric or general abdominal surgery, as well as from the general population in the Montreal area.