Abstract
Constipation-predominant irritable bowel syndrome and functional constipation are common conditions that can have significant negative effects on individuals’ personal lives and social interactions. Treating these conditions can be quite challenging. First-line management typically involves incorporating high-fibre foods, such as fruits, vegetables, and whole-grain cereals, in a habitual diet. However, not all high-fibre foods have laxative properties. Furthermore, limited data is available regarding the effectiveness of specific high-fibre foods and the mechanisms behind their laxative effects.
This PhD thesis studied the role of two fibre foods, green kiwifruit and defatted rice bran fortified bread, in improving bowel habits and gastrointestinal symptoms and functions. Green kiwifruit can improve laxation, increase colonic water content, and potentially modulate human gut microbiota composition. Similarly, high-fibre bread has been shown to improve laxation and constipation symptoms. Defatted rice bran was chosen as a dietary fibre supplement due to its wide availability and low cost, making it an acceptable option for fibre fortification in baked goods. However, more studies are needed to assess the effectiveness and mechanism of green kiwifruit and defatted rice bran-fortified bread on gastrointestinal symptoms and functions.
Two intervention studies were conducted to test the hypotheses: A) that consumption of two green kiwifruit four weeks improves abdominal pain, constipation and other associated symptoms, normalises bowel habits and changes gastrointestinal motility, colonic volume and water content, and colonic hydrogen and carbon dioxide concentrations in individuals with functional constipation and constipation-predominant irritable bowel syndrome: B) that consumption of three to four slices of defatted rice bran-fortified bread for week regularises bowel habits, changes gastrointestinal symptoms, improve general health and well-being, changes gastrointestinal motility, and colonic hydrogen and carbon dioxide concentrations in healthy individuals with low fibre diet.
The consumption of two green kiwifruit daily was associated with improved abdominal pain in individuals with constipation predominant irritable bowel syndrome but not functional constipation. A trend towards improved constipation and increased frequency of complete spontaneous bowel movements per week was observed between interventions. The quality of life increased, but not the other mental health parameters. The relaxation time of colonic chyme in the ascending colon was higher, reflecting higher water content. No change was observed in the whole gut transit time, regional transit time and colonic volume.
Consuming three to four slices of defatted rice bran-fortified bread increased the daily dietary fibre intake, but no change was noted in the bowel habits, gastrointestinal symptoms, transit time, and colonic hydrogen and carbon dioxide concentrations of healthy individuals with low-fibre diets. There was an improvement in the plasma lipid concentration, specifically an increase in high-density lipoprotein cholesterol, also known as good cholesterol.
Consumption of green kiwifruit was linked to laxative effects, as shown by both subjective and objective measures. Consuming defatted rice bran-fortified bread increased dietary fibre intake and showed no changes in gastrointestinal parameters.
The results of this thesis offer additional evidence regarding the effects of high-fibre foods on gastrointestinal symptoms and function. It emphasises the importance of evaluating the effectiveness and mechanisms of specific food items before incorporating them into dietary recommendations.