A new study published in Neurogastroenterology and Motility aimed to demonstrate the utility of magnetic resonance imaging (MRI) in detecting the differences in colonic volumes, transit, chyme consistency, and response to psyllium – an effective constipation treatment, among healthy and constipated subjects. The present study involved two crossover studies. In the first instance, adults without constipation, including 9 controls, took three treatments in a randomized order for 6 days; vis, maltodextrin (placebo), psyllium 3.5 g t.d.s and 7 g t.d.s. In the second case, 20 patients with chronic constipation took placebo and psyllium 7 g t.d.s. for 6 days. MRI was performed fasting and postprandially, on day-6. The results revealed that the 7 g psyllium t.d.s. increased fasting colonic volumes in controls from median 372 mL to 578 mL, and in patients from median 831 mL to 1104 mL. Mean postprandial small bowel water was higher in controls and patients after 7 g psyllium t.d.s. relative to placebo. Additionally, whole gut transit was slower in patients than controls. On MR relaxometry, T1 of the descending colon chyme (fasting) was lower in patients than in controls, but increased by 7 g psyllium t.d.s. Meanwhile, descending colon T1 correlated with baseline stool water content and stool frequency on treatment. From the findings, it was inferred that MRI measurements can objectively demonstrate the mode of action of therapy targeting intestinal fluid content in constipation.