Fasting vs. counting calories: which works better for weight loss?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Female or Male * Age 18-60 years * Body Mass Index 27-46 kg/m2 * Sedentary: defined as \<150 minutes per week of voluntary exercise at moderate intensity or greater and \< 60 min per day of total habitual physical activity (i.e. work related, transportation related) at moderate intensity or greater, over the past 3 months. * No self-report of acute or chronic disease (cardiovascular disease (CVD), diabetes, gastrointestinal disorders and orthopedic problems in particular) * No plans to relocate within the next 12 months * No plans for extended travel (\> 2 weeks) within the next 12 months * No nicotine use * Live or work within 30 minutes of the Anschutz Health and Wellness Center (AHWC) (exceptions may be made at the discretion of the Study PI on a case by case basis for highly motivated subjects). * Capable and willing to give informed consent, understand exclusion criteria, and accept the randomized group assignment. * Have a primary care physician (or are willing to establish care with a primary care physician prior to study enrollment) to address medical issues which may arise during screening or study procedures/interventions. * For Females * Not currently pregnant or lactating * Not pregnant within the past 6 months * Not planning to become pregnant in the next 12 months; * Sexually active women of childbearing potential may be enrolled if they have had a tubal ligation or use a reliable means of contraception Exclusion Criteria * Diastolic blood pressure \> 100 mm of Mercury (HG) or systolic blood pressure \> 160 mm HG. * Resting heart rate \>100 * Diabetes (fasting glucose ≥126 mg/dL or Glycated Hemoglobin (A1C) ≥6.5%) * Undiagnosed hypo- or hyper-thyroidism (TSH outside of the normal range) or history of uncontrolled thyroid disorder. History of thyroid disease or current thyroid disease treated with a stable medication regimen for at least 6 months is acceptable. * Hematocrit, white blood cell count or platelets significantly outside the normal reference range. * Triglycerides \> 400 mg/dL * LDL cholesterol \> 200 mg/dL * Abnormal resting electrocardiogram (ECG): serious arrhythmias, including multifocal Premature Ventricular Contractions (PVC's), frequent PVC's (defined as 10 or more per min), ventricular tachycardia (defined as runs of 3 or more successive PVC's), or sustained atrial tachyarrhythmia; 2nd or 3rd degree A-V block, QTc (Q-T Corrected) interval \> 480 msec or other significant conduction defects. * Presence or history of any metabolic or chronic health problems which would affect appetite, food intake, energy metabolism, or ability to optimally participate in the exercise component including: CVD, peripheral vascular disease, cerebrovascular disease, significant cardiac arrhythmias or cardiac valve disease, diabetes, uncontrolled hyper- or hypothyroidism, uncontrolled hypertension, cancer (within the last 5 years, except skin cancer or other cancers considered cured with excellent prognosis), HIV infection, significant gastrointestinal disorders (described below), significant pulmonary disorders (described below), significant renal, musculoskeletal, neurologic, hematologic, or psychiatric disease. * Significant gastrointestinal disorders including: chronic malabsorptive conditions, peptic ulcer disease, Crohn's disease, Ulcerative Colitis, chronic diarrhea, or active gallbladder disease. * Significant pulmonary disorders including: chronic obstructive pulmonary disease (COPD), interstitial lung disease, cystic fibrosis, or uncontrolled asthma. * Symptoms suggestive of CVD: chest pain, shortness of breath at rest or with mild exertion, syncope. * Regular use of prescription or over-the-counter medications known to significantly impact appetite, weight, or energy metabolism * Regular use of systemic steroids (other than Oral Contraceptive Pills). * Regular use of obesity pharmacotherapeutic agents within the last 6 months. * Previous obesity treatment with surgery or weight loss device, except: (1) liposuction and/or abdominoplasty if performed \> 1 year before screening, (2) lap banding if the band has been removed \> 1 year before screening, (3) intragastric balloon if the balloon has been removed \> 1 year before screening (4) duodenal-jejunal bypass sleeve, if the sleeve has been removed \> 1 year before screening or 5) AspireAssist or other endoscopically placed weight loss device if the device has been removed \> 1 year before screening. * Current alcohol or substance abuse * Nicotine use (past 6 months) * History of clinically diagnosed eating disorders including anorexia nervosa, bulimia, binge eating disorder. * Current severe depression or history of severe depression within the previous year, based on Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) criteria for Major Depressive Episode. * History of other significant psychiatric illness (e.g. psychosis, schizophrenia, mania, bipolar disorder) which in the opinion of the Study MD would interfere with ability to adhere to dietary or exercise interventions. * Currently participating in or planning to participate in any formal weight loss or physical activity programs or clinical trials. * Weight loss \>5kg in past 3 months for any reason except post-partum weight loss, weight gain \>5kg in past 3 months requires assessment by PI to determine reason for weight gain and if it is appropriate for the subject to participate in the study.