FOGA Randomised Controlled Trial of the Effect of the Low FODMAP Diet and Dietary Oligofructose on Gastrointestinal Form, Function and Microbiota in Healthy Volunteers

Oligofructose (OF) is a fructose- based oligosaccharide and defined in the European Union as a dietary fibre. Enzymatically derived from the longer chain inulin in chicory, it is commonly used in processed food to improve mouth feel in fat-free products. OF is poorly digested and absorbed in the small bowel so passes to the colon where it is fermented by the bacteria usually resident in the colon, termed the microbiota. This process produces gases such as hydrogen and sometimes methane, and short-chain fatty acids (SCFAs) which have a variety of roles including nutrition to colonocytes, immunological effects and modulation of intestinal motility. Its presence in the colon alters the composition of the microbiota, with reported potential benefits to health, leading to its description as a 'prebiotic'. Recently, however, such poorly digested carbohydrates grouped together by the term FODMAP (fermentable oligo-, di-, mono-saccharides and polyols) have been proposed to exacerbate symptoms of irritable bowel syndrome (IBS) such as abdominal discomfort and bloating. Dietary exclusion of foods containing FODMAPs, such as wheat, dairy and certain fruit and vegetables, has been proposed as a treatment for IBS, with some evidence to support this. FODMAPs are thought to induce symptoms either by drawing water into the small bowel by osmosis, or through gaseous distension of the large bowel or a combination of these along with metabolite effects on motility. The Nottingham GI MRI group has been at the forefront of elucidating the actual effects of FODMAPs on gastrointestinal (GI) physiology. We have published techniques to measure small bowel water content, colonic volume and gas volume and whole gut transit time. We have recently demonstrated that a single, large (40g) dose of inulin leads to an increase in colonic volume, mainly through an increase in colonic gas. Such a dose is beyond the usual range of dietary variation, however. Last year we piloted a model more similar to dietary practice. Participants supplemented their usual diet with 5g OF twice daily for a week. The most striking result was an 18% increase in fasting colonic volume. This could not be explained by changes in colonic gas and may represent proliferation, and increased mass, of the microbiota. That study was an open label, uncontrolled case series so we now wish to test the hypothesis in a double-blind, randomised controlled trial. For explanatory purposes we will also measure whole gut transit, colonic gas volume and hydrogen and methane expired in the breath. For exploratory purposes we will also collect stool and urine samples to allow assessment of the effect on microbiota and their metabolic output.