SIGGAARD, REGITZE, ANNE RABEN AND ARNE ASTRUP. Weight loss during 12 weeks' ad libitum carbohydrate-rich diet in overweight and normal-weight subjects at a Danish work site. Obes Res. 1996;4:347-356. The effect of 12 weeks' ad libitum carbohydrate-rich, low-fat diet on total body weight, lean body mass, and fat mass was studied in a group of healthy subjects at a Danish work-site (I) (n=50, BMI = 28.4 ± 0.7 kglm 2). Sixteen sublects served as controls (C) (BMI = 27.0 ± 1.0 kglm ). After 12 weeks the I subjects had decreased their fat intake from 39.0 ± 1.1 energy-% (E %) to 28.0 ± 1.2 E % and increased their carbohydrate intake from 46.0 ± 1.1 E% to 56.4 ± 1.1 E% (p<0.05 vs. C). Moreover, a significant loss of body weight (4.2 ± 0.4 kg) and fat mass (4.4 ± 0.6 kg) was observed in I (p < 0.05 vs. C). The weight loss in I was not regained at 24 and 52 weeks' follow-up (82% of I participating) compared to baseline. The cost per kg lost weight amounted to $14.7/person. In conclusion, instructions at a work site in ad libitum intake of a carbohydrate-rich, low-fat diet resulted in a significant loss of body weight and fat mass in overweight and normal-weight subjects.