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.

Inclusion Criteria:

We are recruiting two groups of sedentary or untrained males and pre-menopausal females (age 25-40 years) with body mass indices (BMI) between 30.0-39.9 kg/m^2. All participants will be required to provide a medical record and/or photographic evidence of weight at childhood (around age of 10-17 years old). Individuals with BMI between 40.0-41.9 may be included in the case that an individual with a much shorter height falls within this range, as BMI does not always properly define obesity type. Once the participant completes their DEXA scan, we will be able to more accurately assess the participant's obesity level and re-evaluate their elgibility.

Exclusion criteria:

Participants will be excluded if they are pregnant or planning to become pregnant, breast-feeding, presently using nicotine containing products (e.g. cigarettes, chewing tobacco, nicotine gum etc.), taking certain anti-depressants and anti-hypertensives. More modern medications will not need to be excluded as they don't affect weight loss or weight gain. As medication use will be screened, if the participant is using medications that do not affect our outcomes they will be included in the study. Participants will also be excluded if they have had any surgery (e.g. gastric bypass, magnetic implants) or have any conditions (e.g. iron deficiency anemia) or diseases (e.g. diabetes, cancer, IBD, history of eating disorders or mental illness) that may affect immune function and thus study outcomes, or the ability to participate in the study.

Participants must also have been weight stable for at least 2 months.

Sedentary or untrained individuals with body mass index between 30.0-39.9kg/m^2 (see conditions above).