Healthy diets for a healthy weight: exploring physiological mechanisms related to dietary fibre and non-nutritive sweeteners

Challenges

A key challenge for researchers and policymakers is to produce and implement evidence-based guidelines for the UK food system to reduce obesity trends. Some 65% of the Scottish adult population is classified as living with overweight or obesity. In general, the Scottish diet is poor quality being too high in calories, processed foods, fats, sugar, and salt; it is equally too low in fibre, oily fish, and vegetables. Poor diets are a major contributory factor driving diet and health inequalities. Diet inequalities are notably socially patterned according to socio-economic status, where overweight and obesity prevalence is higher in socially disadvantaged groups.

Dietary fibre is found inherently in plant derived foods and is indigestible in the small intestine but can be a substrate for fermentation by the microbiota that primarily inhabits the lower gut. This can result in a rise in fermentation products such as short-chain fatty acids which are thought to confer several health benefits, including appetite control and suppression of food intake. Although increased fibre intake can be helpful, it is still a relatively underexploited dietary approach to tackle obesity. Therefore, foods containing fibre, that promote satiety and reduce energy intake, may be promising tools in weight management.

Further, food additives, such as artificial sweeteners or non-nutritive sweeteners, could influence the response to dietary fibre via the gut microbiota, which are tiny bacteria that live in the gut.  There is emerging evidence that some sweeteners could disturb the normal balance of the gut microbial ecosystem. Replacing sugar with non-nutritive sweeteners may inhibit the growth of bacteria for a healthy gut microbiome and may even promote harmful bacteria and/or metabolites. For humans to benefit from dietary fibre, fermentation is essential. This will not happen effectively if additives reduce the beneficial bacteria needed for this process. Furthermore, some non-nutritive sweeteners may prevent weight loss if microbiota disruption adversely affects satiety signalling from the gut. Indeed, reports suggest that some non-nutritive sweeteners are associated with weight gain and obesity as well as disrupted blood sugar control, thereby being potentially as harmful as the sugary drinks they replace.

In Scotland, there is a ‘fibre gap’, with the population consuming well below the recommended levels for good health. It is crucial to explore the reasons for inherently low fibre intake by considering the attitudes of Scottish consumers to dietary fibre and its link to health using a consumer survey approach. Furthermore, there is a need for a move away from a meat-based diet towards increased fibre intake for health reasons, as well as to transition towards a sustainable, environmentally friendly food supply. These issues appear to be being largely missed or ignored by consumers in Scotland.

Questions

Solutions

This project aims to understand the physiological role of dietary fibre in the regulation of appetite and its role in achieving a healthy weight and also the potential interference of food additivities (non-nutritive sweeteners) on this physiological response.

Attitudes of Scottish consumers to dietary fibre and non-nutritive sweeteners 

We are exploring public attitudes towards artificial sweeteners and dietary fibre. To achieve this, we conducted a consumer survey to draw upon respondents' attitudes, feelings, beliefs, experiences and reactions to questions on both dietary fibre and non-nutritive  sweeteners. The range of respondents reflected consumers across Scotland and England and was biased towards individuals living with overweight and obese from all geographical areas. We are investigating responses with a view to highlight relevant and potentially modifiable interventions and leverage points likely to effect changes. The results will be disseminated to obesity and poverty alleviation advocacy groups, also food system and public health policy stakeholders.

Exploring the efficacy and physiological responses to a high-fibre (pectin) diet

We initiated a controlled diet trial with healthy but overweight/obese individuals to investigate the key dietary components of physiological mechanisms associated with appetite control for a healthy weight, mediated by gut hormone release. This approach addressed the impact of dietary fibre on people living with obesity and food inequalities. The outcome of this study was to highlights the importance of habitual fibre intake as a potential modulator for gut microbiome activity and composition. This study was terminated due to funding cuts.

Effects of a non-nutritive sweetener with a high-fibre diet on metabolic health and composition of gut microbiota

We are focussing on conducting a controlled dietary intervention study to assess the impact of a non-nutritive sweetener (sucralose, a common synthetic food additive) on a high-fibre diet, on gut microbiota activity and composition and makers of metabolic health. We are also exploring how the inclusion of high-fibre and non-nutritive sweeteners influence blood sugar or glycaemic control.

Overall, this project will potentially provide policymakers with important insights related to increasing fibre consumption across the population - a key public health target. Additionally, fibre is a naturally high component of plant-based foods such as fruits and vegetables, grains, nuts and legumes, which ought to be increased at the expense of meat to address the issue of sustainable diets. Lastly, sugar replacers are being widely used by the food industry to overcome the sugar levy, so it is important to ensure there are no unintended consequences.

Project Partners

Progress