Under the supervision of a registered dietitian, subjects will receive an individualized dietary prescription that incorporates a methionine-free amino acid-modified medical food (Hominex- 2, Abbott Nutrition) supplemented with low-methionine foods. Hominex-2 contains a mixture of L-amino acids but lacks methionine. Subjects will be instructed in the preparation of Hominex-2 beverages (4-5 per day) to deliver 100% of daily protein requirements (0.8 g/kg/day) and 40-45% of the caloric requirements. The remaining calories will be met with low-methionine foods, including fruits, vegetables, grains (e.g., specified cereal and bread), margarine and cooking oils. Subjects will be provided with a list of foods that are low in methionine. Calories will not be restricted. Subjects will be encouraged to follow their usual level of physical activity and instructed to maintain a daily diet and exercise diary that will be reviewed weekly by the dietitian.