Twenty-four hour energy expenditure during a standard physical activity programme was investigated in 19 healthy volunteers in a randomized, double-blind, cross-over design, after supplementation with a soluble dietary fibre amounting 7 g/day for 2 weeks. Energy intake and food fibre intake were kept constant during the treatment period. Twenty-four hour energy expenditure decreased insignificantly during fibre treatment (1.3 +/- 1.7 per cent). The dietary fibre supplement also had no significant effect on body weight, faecal energy loss or heart rate. Systolic blood pressure was insignificantly reduced during both placebo and fibre treatment (P = 0.09). There was, however, no difference between the groups after treatment.