The Effect of the Low FODMAP Diet and Dietary Oligofructose on Gastrointestinal Form, Function and Microbiota

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.

Inclusion criteria

• Aged 18 or older
• Able to give informed consent

Exclusion criteria

• Self-declared vegetarian, vegan or kosher/ halal diet who cannot eat carmine red dye
• Pregnancy declared by candidate
• History declared by the candidate of pre-existing gastrointestinal disorder that may affect bowel function
• A positive diagnosis of irritable bowel syndrome based on the Rome III criteria questionnaire
• Reported history of previous resection of the oesophagus, stomach or intestine (excluding appendix)
• Intestinal stoma
• Any medical condition making participation potentially compromising participation in the study e.g. diabetes mellitus, respiratory disease limiting ability to lie in the scanner
• Contraindications for MRI scanning i.e. metallic implants, pacemakers, history of metallic foreign body in eye(s) and penetrating eye injury
• Will not limit alcohol intake to ≤ 35 units/ week and ≤ 8 units per day during trial
• Unable to stop drugs known to alter GI motility including mebeverine, opiates, monoamine oxidase inhibitors, phenothiazines, benzodiazepines, calcium channel antagonists for the duration of the study (Selective serotonin reuptake inhibitors and low dose tricyclic antidepressants will be recorded but will not be an exclusion criteria)
• Antibiotic or prescribed probiotic treatment in the past 8 weeks
• Inability to lie flat or exceed scanner limits of weight <120kg
• Poor understanding of English language
• Participation in night shift work the week prior to the study day. Night work is defined as working between midnight and 6.00 AM
• Participation in any medical trials for the past 3 months
• Anyone who in the opinion of the investigator is unlikely to be able to comply with the protocol e.g. cognitive dysfunction, chaotic lifestyle related to substance abuse