Low-Fat Vegan Diet Versus a Mediterranean Diet on Body Weight

Inclusion Criteria: * Men and women age ≥18 years of age * Body mass index 28-40 kg/m2 Exclusion Criteria: * Diabetes mellitus type 1, history of any endocrine condition that would affect body weight, such as thyroid disease, pituitary abnormality, or Cushing's syndrome * Smoking during the past six months * Alcohol consumption of more than 2 drinks per day or the equivalent, episodic increased drinking (e.g., more than 2 drinks per day on weekends), or a history of alcohol abuse or dependency followed by any current use * Use of recreational drugs in the past 6 months * Use within the preceding six months of medications that affect appetite or body weight, such as estrogens or other hormones, thyroid medications (unstable dose within the preceding 6 months), systemic steroids, antidepressants (tricyclics, MAOIs, SSRIs), antipsychotics, lithium, anticonvulsants, appetite suppressants or other weight-loss drugs, herbs for weight loss or mood, St. John's wort, ephedra, beta blockers * Pregnancy or intention to become pregnant during the study period, as verified by self--- - Unstable medical or psychiatric illness * Evidence of an eating disorder * Likely to be disruptive in group sessions * Already following a low-fat vegan diet or Mediterranean diet * Lack of English fluency * Inability to maintain current medication regimen * Inability or unwillingness to participate in all components of the study * Intention to follow another weight-loss method during the trial