Seventeen obese adolescents were treated with the protein-sparing modified fast (PSMF), a high-protein, low-carbohydrate, low-calorie diet, for approximately 3 mo and then followed for a total of 12 mo. The diet provided a mean of 880 kcal.kg-1. d-1 and 2.5 g protein. kg IBW-1. d-1. Body composition was determined using four skinfold measurements, total body potassium (TBK), and total body nitrogen (TBN) at baseline, 3 mo, and 12 mo. Twelve subjects returned for follow-up at 1 y (71%) and 48% had sustained weight loss with the percentage ideal body weight for height decreased from 154 to 125 over the year. Six subjects had TBK and TBN measured and TBK decreased 13.0% and TBN decreased 14.3% over the year. This reflected a change toward normalization of the predicted TBK from 121 to 102% and TBN from 119 to 102%.