Irritable Bowel Syndrome (IBS) is a highly prevalent condition of the gastrointestinal tract that has significant impact on sufferer's quality of life. The diarrhoea variant (IBS-D) makes up around one third of all IBS sufferers. There is currently a lack of both effective pharmacological and non-pharmacological treatments for IBS-D. Three food supplements: Green tea, vitamin D and curcumin have all been shown to demonstrate benefit in either reducing symptoms in IBS or diarrhoea as individual ingredients, but have never been tested in combination to assess their effectiveness in IBS. This research study aims to examine the effectiveness of green tea, vitamin D and curcumin in combination compared to a placebo capsule in individual suffering from IBS-D. The study will aim to enroll 78 participants with IBS-D and utilise a placebo-controlled double blind design. The study will consist of a 2 week screening period, a 4 week randomised treatment period (50% participants to receive placebo, 50% to receive active treatment), followed by a 4 week open label treatment period (all participants to receive the active study product).