The study will describe the composition of weight loss in diabetic subjects at the tissue/organ level of body composition; specifically, to determine whether and to what degree different tissues and organs are conserved or lost in comparison to total fat free mass (FFM) change during weight loss. The study will also assess the effects of aging on organ and tissue mass in 50+ year old diabetic men and women in a control group. The study will test whether a portion of weight loss related changes in resting energy expenditure (REE) can be explained by changes in the relative fractions of body mass as high (brain, heart, liver, kidney) and low (skeletal muscle, adipose tissue) metabolic activity tissues with respect to oxidative metabolism in 50 plus year old diabetic men and women. A secondary aim is to assess the effects of weight loss on cardiac structure and function using cardiac gated MRI. Consenting, eligible Look AHEAD participants at St. Luke's and at the University of Pittsburgh will participate in MRI and REE tests. Seventy men and women will be measured, equally distributed between the two sites, and equally distributed between Lifestyle Intervention group and a Community Care group. Measures will be acquired at baseline, following one year of intervention (Year 1), and following one year of maintenance (Year 2), to produce a 2 X 3 factorial design.