Abstract Ninety-seven mildly obese females (BMI = 27.4 kg/m2) were in a randomized, double-blind, placebo-controlled trial treated for 52 weeks. The treatment consisted of a hypocaloric diet providing 5000 kJ/day (1200 kcal) and a dietary fibre supplement of 7 g/day for 11 weeks, (part I), followed by a diet providing 6720 kJ/day (1600 kcal) and a dietary fibre supplement of 6 g/day for 16 weeks (part II). Finally placebo was withdrawn and all still adhering subjects were given a dietary fibre supplement of 6 g/day and an ad libitum diet for the rest of the period (part III). Initial body weights were comparable, 76.9 +/- 0.8 kg in the fibre group versus 77.7 +/- 1.3 kg in the placebo group. During part I the weight reduction in the fibre group of 4.9 kg was significantly higher compared to that of 3.3 kg in the placebo group (P = 0.05). Accumulated weight reduction during part II was still significantly higher in the fibre group, 3.8 kg, compared to 2.8 kg in the placebo group (P less than 0.05). Total weight loss in the fibre group after 52 weeks was 6.7 kg. Probability of adherence to the treatment regimen was significantly higher in the fibre group from week 13 and onwards (P less than 0.01). Initial blood pressures were comparable. A significant reduction of systolic blood pressure occurred in both groups. A significant reduction of diastolic blood pressure occurred in the fibre group only, from 85.4 +/- 1.2 mmHg to 81.7 +/- 1.1 mmHg (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)