Nutrition Bulletin

Summary  Resistant starch (RS) refers to the portion of starch and starch products that resist digestion as they pass through the gastrointestinal tract. RS is an extremely broad and diverse range of materials and a number of different types exist (RS1–4). At present, these are mostly defined according to physical and chemical characteristics. RS may be categorised as a type of dietary fibre, as defined by the American Association of Cereal Chemists and the Food Nutrition Board of the Institute of Medicine of the National Academies. RS is measured in part by the methodology recommended by the Association of Official Analytical Chemists for measuring dietary fibre. Dietary intakes of RS in westernised countries are likely to be low. However, accurate comparative assessments of dietary intakes between countries, and subsequent epidemiological analysis, are absent due to the lack of consensus over of an agreed, repeatable and simple in vitro method for analysing the RS content of foods. At present, the recognised method is that of McCleary & Monaghan (2002). RS appears to confer considerable benefits to human colonic health, but has a smaller impact on lipid and glucose metabolism. Comparisons between studies are hampered by differences in study design, poor experimental design and differences in the source, type and dose of RS in the ingredients or diets used. It is likely that RS mediates some or all of its effects through the action of short chain fatty acids but interest is increasing regarding its prebiotic potential. There is also increasing interest in using RS to lower the energy value and available carbohydrate content of foods. RS can also be used to enhance the fibre content of foods and is under investigation regarding its potential to accelerate the onset of satiation and to lower the glycaemic response. Due to the difficulties in agreeing on a universal definition and method of analysis for dietary fibre, RS may be included within the term ‘fibre’ on the nutrition labels in some countries but not in others. Pressure to agree a legal definition and universal method of analysis is likely to increase due to the potential of RS to enhance colonic health, and to act as a vehicle to increase the total dietary fibre content of foodstuffs, particularly those which are low in energy and/or in total carbohydrate content.

Summary  The health benefits of including sufficient dietary fibre in the diet have been well described and have formed the basis of dietary recommendations around the world. However, dietary fibre is a complex dietary entity, consisting of many non‐digestible components of food. Debate surrounding the definition and measurement of dietary fibre has resulted in inconsistencies in labelling, description and recommendations set across the world. In the UK, dietary recommendations are made using the fraction of non‐digestible material described as non‐starch polysaccharide that is measured by the Englyst method. However, the Association of Official Analytical Chemists (AOAC) methods, used widely by the food industry, capture a much greater range of non‐digestible material, that some suggest should be included in any definition of dietary fibre. An attempt to resolve such discrepancies, possibly by taking an approach that considers the health effects of fractions not captured in the Englyst method, is probably overdue.

Additionally, it is clear that the effects of these various non‐digestible components of dietary fibre are not interchangeable, and it is important that fibre comes from a range of sources to ensure maximum health benefits from the fibre in the diet. Traditional ‘insoluble’ fibres are required to add bulk as well as rapidly fermentable, viscous fibres to bring about cholesterol lowering. There is also a convincing argument for including slowly fermented components, such as resistant starches, that are well tolerated in the digestive system and can bring about improvements in gut function. Currently there is insufficient data from well designed human intervention trials to make specific recommendations on the amounts of these fibre components in the diet, but it may be useful for health professionals to talk in terms of the different food sources of these types of fibre, as well as total fibre amounts.

The merits of a fibre‐rich diet are well documented. Resistant starch (RS) is a form of starch that resists digestion in the small intestine and, as such, is classified as a type of dietary fibre. RS can be categorised as one of five types (RS1–5), some of which occur naturally in foods such as bananas, potatoes, grains and legumes and some of which are produced or modified commercially, and incorporated into food products. This review describes human evidence on the health effects of RS consumption, with the aim of identifying any benefits of RS‐rich foods and RS as a functional ingredient. The reduced glycaemic response consistently reported with RS consumption, when compared with digestible carbohydrate, has resulted in an approved European Union health claim. Thus, RS‐rich foods may be particularly useful for managing diabetes. There appears to be little impact of RS on other metabolic markers, such as blood pressure and plasma lipids, though data are comparatively limited. Promising results on markers of gut health suggest that further research may lead to the classification of RS as a prebiotic. Microbial fermentation of RS in the large intestine to produce short‐chain fatty acids likely underpins some of its biological effects, including increasing satiety. However, effects on appetite have not resulted in notable changes in bodyweight after long‐term consumption. Emerging research suggests potential for RS as an ingredient in oral rehydration solutions and in the treatment of chronic kidney disease. Overall, RS possesses positive properties as a healthy food component.

Sustainable diets are proposed as a means to improve public health and food security and to reduce the impact of the food system on the environment. Guidance around sustainable diets includes a reduction of animal products in order to move towards a more plant‐based diet, meaning that plant‐originated foods are a predominant, but not the sole component of a diet. The main principles of a sustainable diet (as provided by the Food and Agriculture Organization of the United Nations/World Health Organization) are to consume a variety of unprocessed or minimally processed foods, mainly as wholegrains, pulses, fruits and vegetables, with moderate amounts of eggs, dairy, poultry and fish and modest amounts of ruminant meat, which are consistent with the current UK healthy eating recommendations (e.g. Eatwell Guide). The aim of this review was twofold: (i) to discuss public health challenges associated with consumers’ knowledge regarding protein sustainability, healthier protein sources and protein requirements, and (ii) to review potential approaches to facilitate the shift towards a more sustainable diet. Consumers would benefit from receiving clear guidance around how much protein is needed to meet their daily requirements. The public health message directed to a consumer could highlight that desired health outcomes, such as muscle protein synthesis and weight control, can be achieved with both sources of protein (i.e. animal and plant‐based), and that what is more important is the nature of the ‘protein package’. Health promotion and education around the benefits of plant‐based protein could be one of the strategies encouraging the wider population to consider a shift towards a predominantly plant‐based diet.

Personalised nutrition can be defined as developing unique nutrition guidelines for each individual; precision nutrition seeks to develop effective approaches based on the combination of an individual's genetic, environmental and lifestyle factors. The former infers variants that underlie traits are largely fixed (i.e. stable across time) and appeals to the notion that we are inherently different from one another. The latter opens up the possibility that what we do and where we are may be more important than what we are. While there are undoubtedly a specific minority of individuals who clearly require a more personalised approach to nutrition, several criteria must be fulfilled before we can justify or implement personalised nutrition for the general population. These would include identifying a desired health outcome and a valid predictor of how that outcome changes, which can be measured with sufficient accuracy and exhibit a robust correlation and/or causal relationship in the required direction (i.e. predictor‐response). Many attempts to personalise nutrition, such as profiling the genome or microbiome, do not currently meet all these criteria. Therefore, we argue that there is presently insufficient rationale for truly personalised nutrition for the majority of people based on the inter‐individual differences that separate them. Conversely, we propose that precision nutrition based on the environmental and/or behavioural ‘lifestyle’ variance within each person may provide a more effective basis for adjusting diet dynamically, with recognition of varying physiological demands and requirements over time.