The effect of one week of supplementation with a water-soluble fibre (guar gum) was studied in obese women who had lost weight. In study 1 (N=17; mean+/-SEM: age 38.5+/-2.3 yrs; weight 86.8+/-2.3 kg; BMI 32.2+/-0.9 kg.m-2) energy intake and hunger and satiety scores were assessed under free-living conditions. In study 2 (N=14; age 44. 5+/-1.8 yrs; weight 78.8+/-3.1 kg; BMI 29.0+/-0.9 kg.m-2) energy intake was fixed at 6 MJ.day-1 (their normal energy intake at that time) or 4 MJ.day-1 (low energy intake). In both studies, the effect of one week of fibre supplementation (40 g in study 1 and 20 g in study 2) was compared with no supplementation. In study 1, mean energy intake decreased significantly from 6.7+/-0.4 MJ to 5.4+/-0.2 MJ daily after fibre supplementation, while hunger and satiety scores did not change. At a low energy intake level of 4 MJ given in study 2, hunger scores were significantly decreased after fibre supplementation. No changes were seen in hunger and satiety scores during fibre supplementation at 6 MJ. The reduction in energy intake by soluble fibre under free living conditions and the hunger-reducing effect of fibre at the low energy intake level (4 MJ) suggests that fibre may be useful in the treatment of obesity, by facilitating compliance to low energy intake.