Effect of Short-Term Beta-Cell Rest in Adolescents and Young Adults With Type 2 Diabetes Mellitus

This study will determine whether resting beta cells (cells in the pancreas that produce insulin) for 2 weeks will improve the ability of patients with Type 2 diabetes mellitus (T2DM) to make insulin. Beta cells can rest by giving patients insulin shots. The study will also examine how teenagers with T2DM feel about having diabetes and explore differences between young people with and without T2DM. This study includes patients 12 to 25 years of age with T2DM who are overweight and who were diagnosed within 2 years of enrolling in the study. Healthy individuals of normal weight or who are overweight are also eligible. Candidates are screened with a medical history, physical examination and laboratory tests. Participants with T2DM are assigned to one of two groups. Group 1 takes an anti-diabetes medicine called metformin and follows a diet prescribed by a study staff dietitian for 2 weeks. Group 2 takes metformin, follows the prescribed diet, and receives insulin through a pump under the skin for 2 weeks. During these two weeks, all participants have the following tests: * Frequent blood sugar checks. * Oral glucose tolerance test (routine diabetes test in which blood samples are drawn before and several times after the subject drinks a sugary solution). * Arginine stimulation to test the response of the body to arginine, a normal ingredient of food that stimulates the release of insulin. Two catheters are placed into veins in the arms, one to administer a liquid containing arginine, the other to draw the blood samples. * Ultrasound of the blood vessels in the neck to check for hardening of the arteries. * Metabolism test to measure the amount of oxygen used during rest. The subject breathes normally during rest while wearing a canopy over his or her head for about 20 minutes. * MRI scans of the abdomen to examine the amount of fat in the belly (at the beginning and end of the study) * DEXA scan to determine percent body fat. * Tests to explore quality of life and feelings about health, work or school, friends and family. * Exercise testing on a treadmill or stationary bicycle. * Genetic studies for information on diabetes and obesity. Normal volunteers have blood draws, oral glucose tolerance testing, MRI scan, DEXA scan, psychological testing, exercise testing, and genetic testing.