Weight Loss and Hunger

Inclusion Criteria: 1. 18-55 years of age; 2. non-smoking; 3. obese class I-II (30 kg/m2 ≤ BMI \< 40 kg/m2); 4. weight stable (± 2 kg during the 6 months prior to enrollment); 5. Sedentary (\<2 times/week of 30 min of continuous exercise) In addition, Females will be included if: 1\) premenopausal (2 menses in the 3 months preceding testing, no increase in cycle irregularity in the 12 months preceding testing). Exclusion Criteria: 1. have a current diagnosis of an axis 1 psychiatric disorder (i.e. mood, anxiety and eating disorders); 2. currently use antidepressants, thyroid medication, or any medication that could affect appetite; 3. have a history of cardiac problems or symptoms suggestive of any cardiac condition; 4. have a current diagnosis or history of diabetes, confirmed by a measure of HbA1c during the screening visit; 5. have alcohol intake that exceeds recommendations or alcoholism, or current addictions to opiates, cocaine or stimulants; 6. currently taking monoamine oxidase inhibitors, pressor agents, warfarin, anticonvulsants, phenylbutazone, or tricyclic antidepressants; 7. have uncontrolled thyroid disease; 8. have any osteoarticular condition, or other reasons that would prevent them from achieving the proposed walking targets. In addition, Females will be excluded if they: 1. are pregnant or planning to become pregnant over the course of the study; 2. are peri- or post-menopausal or have had surgically induced menopause.