This project focused on investigating the importance of healthy diets. With the recent introduction of a sugar levy on soft drinks across the UK, the food and drink industry has sought to replace sugars with non-nutritive sweeteners (NNS). Improving the diet to contain less sugar may have unintended consequences, where replacement of sugar with NNS may inhibit the growth of bacteria for a healthy gut microbiome and/or may even produce/promote harmful bacteria and metabolites. Sucralose is one of several sweeteners that survives passage through the small intestine without absorption and reaches the large intestine largely unchanged, where it potentially can interfere with the fermentation processes.  

Our workplan included a consumer survey to capture attitudes and belief followed by a controlled diet study to assess the impact of dietary fibre and NNS on markers of gut health. 

A diet intervention study protocol included consecutive measurements for two weeks of baseline diet, two weeks of dietary fibre run-in, two weeks on high fibre supplemented diet, then finally, two weeks with high fibre plus sucralose. The aim of this research is to understand the physiological role of dietary fibre in the regulation of appetite and its role in achieving a healthy weight and the potential interference of food additivities (non-nutritive sweeteners) on this physiological response.

Our consumer survey, using Qualtrics XMTM software, examined reasons for low dietary fibre intake in Scotland. In total, 1119 adults aged over 18 years participated online, with 610 and 509 respondents from England and Scotland, respectively. Consumers were asked questions on their understanding of what constitutes dietary fibre, their intake habits, their perceptions and beliefs on the benefits to different dietary aspects of health, and intentions of changing their current habits with respect to dietary fibre and non-nutritive sweeteners (NNS) in their diet. The analysis indicated that most consumers are unaware of how much fibre they eat, how much they should eat or how much is in their food, irrespective of age or deprivation (Index of Multiple Deprivation, IMD) area. These data suggest that consumers need to understand or be educated in dietary fibre sources, and that dietary fibre is found in plant-based foods. Furthermore, the health benefits of increased fibre are being missed, thus education appears to be the single most important tool to promote these benefits. Around 50% of our consumers who were living with overweight or obesity regularly consume NNS. Overall, we discovered there is a general lack of awareness of actual consumption due to consumers failing to check labels. 

We successfully completed the human intervention study with the aim of this research being to understand the physiological role of dietary fibre in the regulation of appetite and its role in achieving a healthy weight and the potential interference of the non-nutritive sweetener (NNS), sucralose, on this physiological response. We recruited 10 men and 10 women (mean age 56.5 years [range 31-74] and BMI 34.6 kg/m2 [range 28.2 – 42.7]).  Faecal bacterial DNA was extracted and was sent for sequencing and bioinformatic analysis of the 16S ribosomal sequences, to provide information on bacterial changes in the different diets. At baseline, there was high abundance of Collinsella, which was maintained throughout the study and was highest during the high fibre period. This has previously been reported as a gut bacterium whose abundance is heavily influenced by diet, typically thriving on high-fat, low-fibre, and highly processed diets. During consumption of the dietary fibre and NNS there was a significantly higher abundance % of Bifidobacterium and Anaerostipes. Bifidobacterium in general is considered protective for gut health, because it breaks down complex carbohydrates. The addition of NNS in the diet did not reduce this beneficial bacteria. The study used fructo-oligosaccahrides (FOS) as a dietary fibre source, so this confirms the role of this dietary fibre. Anaerostipes are key cross-feeders that have an important role in short chain fatty acids (SCFA), to convert lactate and acetate into butyrate – both fermentation products. In summary, the dietary intervention study support that increasing dietary fibre in the diet promoted the production of beneficial metabolites and gut bacteria and that introduction of a NNS impacted on composition and activity within the gut microbiota– however, this was not all negative. Further, surprisingly, even with a modest sample size (10 per group), we detected significant sex effects, that are novel. 

The study has now finished and more information is available by downloading the End of Project report. 

The project team are working to complete the final objective, which is a controlled human diet study on non-nutritive sweeteners and dietary fibre; this project completes in March 2025. We have recruited half of the volunteers and on target to complete recruitment by the end of 2024. The study is set up to be conducted as a within-subject design, with all food and beverages provided, to assess interaction of a non-nutritive sweetener with a high-fibre diet, on markers of gut health in humans. This study will allow assessment of the effects of the non-nutritive sweetener (sucralose) with a high-fibre (soluble fibre, fructo-oligosaccharides, FOS) diet on metabolic health and activity and composition of gut microbiota, by a controlled human diet intervention study. We propose to recruit participants living with obesity and which will allow us to examine the time-course of adaptation of the gut microbiome (measured in faecal samples). We will also assess changes in free-living glycaemic control with addition of dietary fibre and bio-markers of health. The results for this study should become available in 2025.

This work is timely and novel with policy and public health interest in the role of ultra processed food (UPF) and health. The results will provide mechanistic information using controlled diets, on the role of food additives on gut microbiome and metabolite activity and composition.

The project team started working towards three objectives, over 3 years, which briefly relate to, (i) a consumer survey, (ii) controlled human diet study on dietary fibre, and (iii) controlled human diet study on non-nutritive sweeteners and dietary fibre. In the first year we obtained ethics approval for the consumer study on attitudes to dietary fibre and non-nutritive sweeteners, and the controlled human diet study on dietary fibre ensuring that our research is rigorous and meets high standards for safety and integrity. One of the main conclusions from the consumer study was the finding that most people are unaware of which foods contain dietary fibre and this may be part of the reason for the Scottish fibre gap, where fibre consumption generally is considerably lower than the daily recommended intake. 

Unfortunately, we terminated the fibre study in order to concentrate on the fibre and artificial sweetener trial. In our current study, our aim is to evaluate the effects of a non-nutritive sweetener with a high-fibre (FOS , fructo-oligosaccharides) diet on metabolic health and activity and composition of gut microbiota by a controlled diet intervention study (Year 2-3). This study is well underway with a full complement of volunteers recruited, and some have already completed the intervention.  The results should become available towards the end of this study in early 2025.

Further information from the survey can be found in the blog: Low consumer fibre intake may be due to confusion over which foods contain fibre