Body mass index and quality of bowel preparation: Real life vs. clinical trials

Obesity is a recognised risk factor for poor bowel preparation in retrospective studies whilst corresponding data in prospective trials are marginally reported. Aims are to evaluate the relation between body mass index (BMI) and preparation quality in retrospective and interventional prospective settings and within a single centre.

Data from a recent colorectal cancer screening registry were retrospectively analysed for the relation between BMI and adequacy of preparation. Patients were categorised as underweight (BMI<20kg/m(2)), normal (20-25kg/m(2)), overweight (25-30kg/m(2)), and obese (>30kg/m(2)). Data from a recent prospective colon preparation trial were similarly analysed.

541 registry patients were included. Multivariate analysis showed BMI to be an independent risk factor for inadequate preparation. Obesity was associated with odds ratio (OR) of 5.3 [95% confidence interval (CI) 1.4-19.8; p=0.01] compared to normal BMI. A significant difference was also noted in underweight but otherwise healthy individuals (OR=11.1, 95% CI 2-60; p=0.005). In the prospective study of 195 patients, obese patients had comparable rates of inadequate preparation to normal-weight individuals (OR=0.7, 95% CI 1.1-3.96; p=0.68). Underweight patients had a significantly worse preparation compared to normal BMI individuals (OR=8, 95% CI 1.1-58; p=0.04).

In real life, bowel preparations in obese individuals have a lower quality in comparison to normal individuals. This finding is not replicated in clinical trials. This discrepancy is likely the result of focused patient education suggesting that this is primarily a dietary compliance phenomenon. Underweight individuals appear to have worse quality of preparation independent of study design or setting.