Look AHEAD: Action for Health in Diabetes

Inclusion Criteria: * Type 2 diabetes * Overweight * BMI of 25 kg/m2 or greater * If on insulin, BMI of 27 kg/m2 or greater * Blood pressure less than 160/100 mmHg * HbA1c less or equal to 11% * Triglycerides less than 600 mg/dl * Willingness to participate Exclusion Criteria: * Unable or unwilling to give informed consent or communicate with local study staff. * Current diagnosis of schizophrenia, other psychotic disorders, or bipolar disorder. * Hospitalization for depression in past six months. * Self-report of alcohol or substance abuse within the past twelve months. * Current consumption of more than 14 alcoholic drinks per week. * Current acute treatment or rehabilitation program for these problems. * Plans to relocate to an area not served by Look AHEAD or travel plans that do not permit full participation in the study. * Lack of support from primary care health provider or family members. * Failure to complete the two-week run-in for dietary intake and exercise. * Weight loss exceeding 10 lbs. in past three months. * Current use of medications for weight loss. * Self reported inability to walk two blocks. * History of bariatric surgery, small bowel resection, or extensive bowel resection. * Chronic treatment with systemic corticosteroids. * Another member of the household is a participant or staff member in Look AHEAD. * Currently pregnant or nursing. * Cancer requiring treatment in the past five years, except for non-melanoma skin cancers or cancers that have clearly been cured. * HIV positive (self-report), due to effects on weight and body composition of HIV and medications used to treat HIV. * Active tuberculosis (self-report). * Cardiovascular disease (heart attack or procedure within the past three months). * Participation in a cardiac rehabilitation program within last three months. * Stroke or history/treatment for transient ischemic attacks in the past three months. * Pulmonary embolus in past six months. * Unstable angina pectoris or angina pectoris at rest. * A history of cardiac arrest. * Complex ventricular arrhythmia at rest or with exercise (e.g., ventricular tachycardia). * Uncontrolled atrial fibrillation (heart rate of 100 beats per minute or more). * New York Heart Association (NYHA) Class III or IV congestive heart failure. * Acute myocarditis, pericarditis or hypertrophic myocardiopathy. * Clinically significant aortic stenosis. * Left bundle branch block or cardiac pacemaker unless evaluated and cleared for participation by a cardiologist. * Cardiac defibrillator. * Heart transplant. * History of aortic aneurysm of at least 7 cm in diameter or aortic aneurysm repair. * Resting heart rate less than 45 beats per minute or greater than 100 beats per minute. * Any abnormality during the maximum exercise stress test that indicates that it would be unsafe to participate in the Lifestyle Intervention. * Angina pectoris. * Significant ST segment depression at low levels of exercise. (ST segment is the flat, isoelectric section of the ECG between the end of the S wave (the J point) and the beginning of the T wave) * Exercise induced ventricular arrhythmias. * Abnormal hemodynamics, such as flat or decreasing systolic blood pressure with increasing workload. * Those at moderate to high risk for cardiac complications during exercise. * Those who are unable to self-regulate activity or understand the recommended activity level. * Renal disease or dialysis. * Chronic obstructive pulmonary disease that would limit ability to follow the protocol. * Self-reported chronic hepatitis B or C or cirrhosis. * Inflammatory bowel disease requiring treatment in past year. * Cushing's syndrome. * Acromegaly. * Amputation of lower limbs as result of non-traumatic causes. * Any major organ transplant.