Twenty-five RCTs, with a total of 1,477 participants, were included in the review.
In terms of study quality, about half (13 out of 25) of the included studies were double-blind, nine were single-blind and the others were considered to be open.
There was no statistically significant difference in SBP between high and low fibre intake (25 trials; -1.15 mmHg, 95% CI: -2.68, 0.39).
High dietary fibre intake significant reduced DBP compared to low fibre (25 trials; -1.65 mmHg, 95% CI: -2.70, -0.61).
Subgroup analyses.
For patients with hypertension (5 trials), there was a statistically significant decrease in both SBP and DBP in the increased fibre group compared with the control group (respectively: -5.95 mmHg, 95% CI: -9.50, -2.40; -4.20 mmHg, 95% CI: -6.55, -1.85). There was no significant heterogeneity between the 5 trials. There was no statistically significant difference between treatments for SBP or DBP in the trials of patients without hypertension (n=20).
Studies with a duration of 8 weeks or longer (13 trials) reported a statistically significant decrease in both SBP and DBP in the increased fibre group compared with the control group (respectively: -3.12 mmHg, 95% CI: -5.68, -0.56; -2.57 mmHg, 95% CI: -4.01, -1.14). There was no statistically significant difference between fibre intakes in SBP or DBP in trials with a duration of less than 8 weeks (12 trials).
In studies with a fibre supplementation of 7.1 g/day or less (11 trials), only DBP was statistically significantly reduced with the high fibre intake (-1.77 mmHg, 95% CI: -3.32, -0.21). In studies with a supplementation of 7.2 to 18.9 g/day (8 trials), both SBP and DBP were statistically significantly reduced (respectively: -3.40 mmHg, 95% CI: -6.14, -0.67; -1.97 mmHg, 95% CI: -3.79, -0.14). In studies with a supplementation of 19 g/day or more (6 trials), there was no statistically significant difference between the increased fibre group and the control group.
When studies were subgrouped by the type of fibre, there was no statistically significant difference between the increased fibre group and the control group in studies that were supplemented with fruit and vegetables (4 trials) and cereal (9 trials). Studies in which fibre was provided by means of a pill (n=8) found a statistically significant decrease in DBP (-2.44 mmHg, 95% CI: -4.26, -0.62), but there was no statistically significant difference in SBP.
There was a statistically significant decrease in DBP in trials in which weight reduction was noted in the intervention group (9 trials; -2.56 mmHg, 95% CI: -4.69, -0.42), but there was no statistically significant difference in SBP.
There was a statistically significant decrease in DBP in parallel group trials (n=17; -1.96, 95% CI: -3.31, -0.62), but there was no statistically significant difference in SBP.
The funnel plots did not indicate the presence of publication bias.