The goal of this randomised controlled trial (RCT) is to compare the efficacy of the newly developed 5Ad diet against the widely researched low fermentable oligo-, di-, monosaccharide and polyols (FODMAP) diet in reducing gastrointestinal symptoms associated with functional bowel disorders/food intolerances.

The primary aims of this RCT are to determine:

• Whether the 5Ad diet is at least as effective as the low FODMAP diet in reducing gastrointestinal symptoms associated with FBDs/food intolerances.
• Whether either the 5Ad diet or the low FODMAP diet are effective in reducing mental and physical fatigue.

To achieve the above aims, an RCT will be conducted with the 5Ad diet in one arm vs the active phase of the low FODMAP diet in the other arm, in a cross-over design with a 7 days washout phase in between. Both dietary protocols will be followed by each participant for 7 days.

Researchers will compare the results from the 2 dietary protocols in order to ascertain the superiority of one over the other in regards to 6 gastrointestinal symptoms (abdominal pain, bloating, flatulence, bowel urgency, straining and incomplete defecation), stool form and frequency of defecation.

Functional Bowel Disorders (FBDs) are characterised by chronic gastrointestinal symptoms including abdominal pain, constipation, bloating, diarrhoea, alternating abdominal symptoms, and irregular frequency of bowel movements among others in the absence of any intestinal abnormality. The prevalence of FBDs ranges from 15 - 20% worldwide, with remarkable economic burden on health systems and significant impact on the quality of life of sufferers. It is estimated that between 60% - 89% of individuals that suffer from FBDs find that foods exacerbate their symptoms. Therefore, dietary therapies are frequently implemented to assist with symptom relief in these individuals.

Although the low FODMAP diet is the most commonly followed diet for the treatment of FBDs, there are concerns regarding it's complexity, restrictiveness, nutritional adequacy, and effectiveness. Therefore, the 5Ad diet was designed to fill a gap in the existing research and to overcome the limitations associated with existing dietary approaches.

Preliminary findings from the first study in 2019 suggested that the 5Ad diet might be a promising universal approach for varying forms and severities of FBDs. Therefore, an RCT is needed to substantiate these previous results. Thus, this RCT aims to determine whether the 5Ad diet is at least as effective as the low FODMAP diet in reducing gastrointestinal symptoms associated with FBDs/food intolerances.

Inclusion Criteria:

Individuals are eligible for the study if all of the following criteria are met:

• Suffers chronically from either constipation, diarrhoea, or an alternation of both, bloating, flatulence or abdominal pain, incomplete defecation, straining and bowel urgency.
• Symptoms must be present for ≥ 2 times per week, with symptom onset occurring at least 3 months prior to participation.
• Participants taking prescribed medications which may affect bowel function are included only if the intake is maintained throughout the entire intervention period.

Exclusion Criteria:

Individuals are excluded from the study if any of the following criteria are met:

• Pregnant.
• Known underlying pathology (e.g., Crohn's disease, ulcerative colitis, celiac disease).
• History of abdominal/gastrointestinal surgery within 1 year prior to participation.
• History of antibiotic use in the last 6 weeks prior to participation.
• Allergic to the foods specified in both the 5Ad diet and the low FODMAP diet.