The Fibre Full Study

This study will systematically investigate the effects of a diet with decreased energy density, reduced glycaemic index, and significantly increased dietary fibre, on post-prandial glycaemic response, satiety, gastrointestinal tolerability and gut microbiota composition and function in individuals with excess body weight (Body Mass Index (BMI) 25-35kg/m2). Hypothesis: The investigators hypothesise that a diet enriched in fibre will be beneficial to post-prandial glycaemic response, well tolerated and satiating, as compared to the standard Western-style diet.

Participants: Healthy men and pre-menopausal, non-pregnant and non-lactating women, 18-45 years of age, with a Body Mass Index (BMI) between 25-34.9 kg/m2 will be recruited (n=20). Study Design: This exploratory study aims to investigate the effects of a fibre-enriched (FR) diet in adults with excess body weight in comparison to a control diet. This randomized, single-blinded, placebo-controlled intervention/trial with a crossover design compares the effects of consumption of fibre-enriched food staples delivered within a full meal plan (fibre-enriched diet plan) with a matched control meal plan (control diet plan). Participants stratified by age and BMI, will be randomly assigned to receive either the control diet or fibre-enriched (FR) diet for 8 days. After these 8 days, a washout period (13 day minimum) will commence, and participants will then crossover to the opposite diet. All foods and prepared meals within the menu plan will be provided to participants for both the control and FR diets. Participants are required to strictly adhere to their assigned meal plan for the 8-day period. Given the higher dietary fibre intake of the FR-diet, the study design incorporates a dose escalation of the fibre content to allow participants on the FR diet to adjust to the increase in dietary fibre intake (4-day reduced dose, wherein study foods contain only a portion of the required dose of fibre, and 4-day full dose, high fibre intake). The effect of the FR diet on satiety and overall food intake will be assessed. Participants on the FR diet and the control diet will be provided with non-fibre enriched snacks which they may consume at designated times each day, if they wish to and in ab libitum. These snacks will be an optional component of the menu plan. All food intakes will be monitored, and all leftovers will be returned to the research team. Additionally, dietary assessments will be completed at regular intervals. Study Treatments: * The FR diet consists of a full meal plan containing engineered common food products with decreased energy density and glycaemic index, in which a large proportion of refined carbohydrates are replaced with dietary fibre. * The control diet consists of a full meal plan with non-fibre enriched food products. Study Outcome measures will include post-prandial glycaemic response, satiety, gastrointestinal tolerability and gut microbiota composition and function in individuals with excess body weight (BMI 25-35kg/m2).