The goal of this study is to understand if there are differences in the fat, muscle and metabolism of individuals who developed obesity during childhood versus those who developed obesity in adulthood. We will do this by having recruited participants undergo subcutaneous adipose tissue biopsies in the abdomen and thigh, a muscle biopsy in the thigh, collect blood and urine samples, a DEXA scan and 3 submaximal exercise tests. participants will also have their resting energy expenditure measured through indirect calorimetry to tailor a targeted weight loss protocol through caloric restriction and cardiovascular exercise (3 times a week). After 10% of weight loss is completed, study participants will repeat all tests during a 2 week weight stabilization period. At 12 weeks into the intervention, indirect calorimetry, DEXA scan and blood tests will be repeated.