The objective of this study was to examine whether a protein-sparing modified fast diet and a hypocaloric balanced diet are effective in a clinic-based dietary intervention implemented in a school setting high-risk weight loss program for superobese (> or = 140% of their ideal body weight for height [IBW] children. A group of children from two suburban public schools in New Orleans, Louisiana were randomized to either dietary-intervention group and control group. Children were followed for 6 months. In the dietary-intervention-group, 12 of 44 superobese children [ages 8.8 to 13.4 years, weight 144% to 212% of IBW] volunteered to participate. In the control group, 7 of 19 superobese children [ages 9.4 to 12.9 years, weight 140% to 195% of IBW] volunteered to participate. During the first 9 weeks, 12 superobese children were placed on a 2520 to 3360 J (600 to 800 Cal) protein-sparing modified fast diet. Subsequently, the diets of all children were increased in a 3-month period 420 J (100 Cal) every 2 weeks until a 5040 J (1200 Cal) per day balanced diet was attained. In both groups, height and weight were obtained at baseline, 10 weeks, and 6 months; and biochemical measurements were performed at baseline and 6 months. At 6 months the 12 superobese children on protein-sparing modified fast diet had a significant weight loss from baseline (-5.6 +/- 7.1 kg, ANOVA p < 0.02); a significant decrease in percentage IBW (-24.3 +/- 20%, ANOVA p < 0.002); and had positive growth velocity Z-score (1.3 +/- 1.6, ANOVA p < 0.05). Six children were not superobese at 6 months. At 6 months eight of 12 children were active participants and 11 of 12 children were followed. Decrease in blood pressure, as well as, downward trends in serum lipids were observed at 6 months. No clinical complications were observed. At 6 months, the 7 control superobese children, when compared with baseline had gained weight (2.8 +/- 3.1 kg, ANOVA p < 0.008); but had no significant change in percentage IBW (-0.3 +/- 5.9%, ANOVA p = 0.61); and had no changes in growth velocity Z-score (0.1 +/- 1.3, ANOVA p = 0.83). These children did not have any change in blood pressure and an upward trend in serum lipids were observed at 6 months. Protein-sparing modified fast diet and a hypocaloric balanced diet appear to be effective in a group of superobese-school-age children in a medically supervised clinic-based program implemented in a school setting over a 6-month period. The efforts of committed clinic staffs, school officials, peers, and family involvement were crucial to the success of this intervention program in promoting and maintaining weight loss over a 6-month period. Further research with a specific comparison of the hypocaloric diets with longer follow-up periods in the school setting is necessary. In the meantime, these diets should be used only with close medical supervision.