BACKGROUND: Potentially, a binding of 5-aminosalicylic acid (5-ASA) to dietary fibres could reduce the systemic absorption and increase the intraluminal amount [corrected]. The purposes of the study were to investigate if: (1) dietary fibres can bind 5-ASA in vitro, and (2) consumption of dietary fibres is related to disease activity in patients with ulcerative colitis (UC) treated with 5-ASA.

METHODS: In vitro: 15 g of Ispaghula Husk, wheat bran, citrus-pectin, or wheat flour were incubated in a 37°C buffered solutions of 5-ASA (1 g/l) for 3 hours at pH 6 and 7. The concentrations of 5-ASA were determined before and after the incubation using HPLC. In vivo: patients with UC were interviewed two to three times during 6 months. The fibre consumption was estimated and related to the disease activity (CAI, CRP, Faecal-calprotectin) and quality of life (IBDQ).

RESULTS: In vitro: 5-ASA was bound to Ispaghula Husk (5.3-10.0 mg/g) and wheat bran (4.6-5.5 mg/g), and to a minor degree to citrus-pectin. No differences were found in relation to pH. In vivo: 29 patients completed the scheduled interviews. No significant changes in fibre consumption were observed over time; however, patients consuming a diet high in fibre (>20 g/day) had significantly lower CRP (p <0.01) and faecal-calprotectin (p <0.01) than those consuming less fibre (<20 g/dg).

CONCLUSIONS: Patients with a high intake of fibre had a lower disease activity than those with low intake. Ispaghula Husk bound 5-ASA in vitro, independent of pH. The effect might be clinically relevant in patients with UC treated with 5-ASA.