Innovative food design to support a healthier diet – exploring the effects of dietary fibre enrichment on functional characteristics, physiological and microbiome effects, and consumer acceptance of staple foods

Introduction: Inadequate dietary fibre intake is a public health concern and has been linked to increased risk of noncommunicable chronic diseases. Food reformulation using isolated fibres offers a practical tool to develop palatable fibre-rich foods with a lower glycaemic index, energy density, and increased microbiome accessibility. However, it is unclear whether isolated fibres can substitute high proportions of refined carbohydrates in foods without compromising functionality or acceptability. Additionally, to our knowledge, no randomised controlled trial (RCT) has evaluated the metabolic and microbiome effects of such foods within a fully controlled diet. The overarching aim of this thesis was to apply innovative food design to systematically replace refined carbohydrates with isolated fibres in three commonly consumed foods, test their techno-functional, nutritional and sensory qualities, and conduct a strictly controlled RCT to determine the effects of a fibre-rich diet including developed products on glycaemia, energy intake, satiety, and the gut microbiome. Methods: Chapters 2-3 present comprehensive reviews of fibre-based nutritional strategies and critically evaluate the evidence supporting the use of isolated fibres, including resistant starch (RS) for improving metabolic health and food functionality. Chapter 4 details the development and characterisation of reformulated bread, pasta, and scones produced by substituting digestible carbohydrates with diverse fibre blends, using two doses (high- and very-high) of dietary fibre. Their nutritional composition, techno-functional properties, and consumer acceptability were evaluated. These products were subsequently incorporated into whole-diet meal plans with matched controlled diets. Chapters 5-6 detail the design and conduct of The Fibre Full Study, a strictly controlled human feeding trial using a single-blinded, randomised crossover-controlled whole-diet approach among adults with excess body weight (BMI 25-35 kg/m2). The intervention comprised of two 8-day dietary periods including a fibre-rich diet and a control diet separated by a ≥13 day washout. The fibre-rich diet included a dose increase, beginning with a high-fibre phase (38-45 g/day) for the first 4-days followed by a very-high-fibre phase (57-67 g/day) for the last four intervention days, while the control diet provided 21-25 g/day of fibre. Ad libitum snacking was allowed at predefined times. The primary outcome was postprandial glycaemic response to study meals measured by incremental area under the curve (iAUC) using continuous glucose monitoring (CGM). Secondary outcomes included energy intake, perceived satiety, glycaemic variability, gastrointestinal symptoms, and microbiome composition and function. Results: Our literature reviews highlight the variability in function and efficacy of the different fibre sources across fibre-based nutritional strategies. Although intrinsic fibre from whole-plant foods demonstrated the most consistent clinical benefits, emerging research illustrates the use of isolated fibres such as RS to improve metabolic markers and support reformulation initiatives. In Chapter 4, very-high-fibre products were developed which substituted 52% (bread), 27% (pasta) and 47.5% (scones) of flour with isolated fibres, with high-fibre recipes using half of these replacement levels. Reformulation reduced the energy contents, in vitro digestibility, and increased the fibre contents of fibre-rich products in comparison to controls. While very-high-fibre products showed a decrease in quality characteristics and overall acceptability compared to controls, the high-fibre formulations showed consistent high overall consumer acceptability. Incorporating fibre-rich products into study meal plans led to decreases in daily energy content and increases in fibre content to 38-45 g/day and 57-67 g/day for the high and very-high-fibre diets respectively. The RCT demonstrated that the fibre-rich diet was well tolerated and accepted, with no overall increases in gastrointestinal symptoms. The fibre-rich diet significantly reduced postprandial glycaemic responses. Postprandial iAUC significantly decreased at breakfast and lunch with greatest effects on the very-high-fibre phase. Average daily mealtime iAUC was lower on the very-high-fibre diet than on the control (p<0.05). Twenty-four-hour glycaemic variability (CV) also decreased across both fibre-rich phases versus control (all p<0.05). Total daily energy intake was lower on the fibre-rich diet (p<0.001), with no compensatory increase in snacking. Microbiome analyses showed a reduction of branched-chain fatty acid (BCFA) concentrations and the BCFA:SCFA ratio and increases in fibre-degrading taxa with the fibre-rich diet compared to the control. Regression analysis indicated that postprandial glycaemic response did not predict energy intake. Instead, greater abundances of fibre-degrading taxa, and lower BCFA:SCFA ratios predicted lower energy intake. Conclusions: This thesis highlights that innovative food design using isolated fibres offers a pragmatic strategy to produce palatable, nutritionally improved foods capable of altering metabolic and microbiome outcomes. When incorporated into a whole-diet, very-high-fibre reformulated foods reduced postprandial glycaemia, lowered energy intake, maintained satiety, and shifted microbial metabolism. These findings provide new mechanistic and clinical evidence supporting fibre-reformulation as a practical and scalable public health strategy to help close the population fibre gap and support metabolic health.

Grantor dc:publisher

University College Cork

Year dc:date.issued

2026

Author dc:creator

• Walsh, Sarah Kate

Advisors dc:contributor.advisor

• Lucey, Alice
• Walter, Jens

• Dietary fibre
• Food reformulation
• Resistant starch
• Glycaemic response
• Energy intake
• Satiety
• Gut microbiome
• Randomised crossover trial

Statement dc:rights

• © 2026, Sarah Kate Walsh.

Licence dc:rights.uri

• https://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10468/18908

OAI identifier oai:identifier

oai:cora.ucc.ie:10468/18908