Fibre in a plant-based diet

All you need to know about the role of fibre in a plant-based diet, from science to practice in helping citizens achieve their fibre recommendation.

Summary

• Dietary fibre is the non-digestible part of plant foods that is linked to a range of health benefits. Research continues to deepen our understanding of its impact on human health.

• In Europe, fibre intake is below recommendations, likely due to increasingly Western-style diets. This is considered a public health concern due to the link between low fibre diets and chronic disease.

• Dietary fibre has two main functions that support health: increasing faecal bulk and promoting healthy populations of bacteria in the human gut microbiome including short chain fatty acid (SCFA) production. These functions are linked to a reduction in diseases such as bowel cancer, heart disease, and type 2 diabetes.

• Fibre is naturally found in plant-foods, which is considered to be one of the reasons for beneficial health outcomes for those on plant-based diets. Plant-based diets also contain an abundance of other protective substances such as antioxidants and phytochemicals.

• Due to the positive impact on both human health and the environmental footprint of our food, plant-based diets are promoted by many national and organisational dietary guidelines and the World Cancer Research Fund Cancer Prevention and Survival Continuous Update Project.

• Behaviour change towards increasing dietary fibre presents a challenge, but personal motivations and realistic and practical dietary tweaks are helpful when supporting patients. Unified support from government and industry is also required.

• When counselling patients, it is important to address barriers such as fear of gastrointestinal changes, affordability, cooking skills, taste and meeting other nutrient needs and to identify practical opportunities to incorporate high fibre foods at each meal occasion.

Introduction (classification and properties)

Dietary fibre is a broad term used for the portion of plant matter, more specifically complex, non-starch carbohydrates and lignan(1), that resists enzymatic breakdown in the human digestive system and therefore remains intact upon entry to the large bowel.

As plant foods are an exclusive source of fibre, a plant-based or plant predominant diet is, by default, higher in fibre.

Health benefits of dietary fibre have been long-established and widely recognised.

Nevertheless, the continuing investigation into fibre is furthering our understanding of its profound impact on human health along with the mechanisms that underpin it.

The interaction between dietary fibre and bacteria of the colon, known as the gut microbiome, is where many of the observed benefits originate.

Fibre has historically been categorised as either ‘soluble’ (e.g., pectin, beta-glucan), or ‘insoluble’, (e.g., cellulose, lignin), but these categorisations are now thought to have limited links to functionality in the human gut(2).

Categorising fibre according to fermentability, viscosity, and other physiological properties might be more appropriate(3).

The fibre gap challenge

The European Food Safety Authority (EFSA) recommended at least 25g of fibre per day for healthy adults, and most European dietary guidelines recommend between 25 and 35g per day with lower amounts recommended for children from 2 years(4,5).

These recommendations are based on strong evidence that fibre is associated with a lower risk of many of our most common non-communicable diseases including cardiovascular disease, type 2 diabetes and bowel cancer(6).

In addition, low fibre diets are listed as a dietary risk factor for disease in 195 studied countries worldwide(7).

Fibre intakes fall short of recommendations across all age groups in Europe, as shown in table 1, with male adults reaching a daily average of 18-24g and females just 16-20g(5).

These figures are of public health concern based on the wide range of health benefits observed for those with diets high in fibre.

Table 1. Example of adult fibre intake from the UK and European countries(8,5)

Table 2. Percentage (%) contribution to fibre intake from food groups in adults across some European countries(5)

The main sources of dietary fibre across Europe are grains and grain products, as shown in table 2.

Intake from vegetables, potatoes and fruit varies, with warmer southern countries appearing to have a higher contribution from fruit.

In UK data, 18% of fibre intake is from white bread, chips and potato products, biscuits, buns, cakes, pastries and fruit pies(9). These are lower fibre food products, and this data demonstrates a reliance on foods that are generally not considered health promoting.

Health benefits of fibre in the diet

Research consistently links increased intakes of dietary fibre to beneficial health outcomes in humans(10, 11). Many of the benefits are found as a result of the interaction between fibre and the human gut microbiome. The gut microbiome refers to the large population of microorganisms that live within the human digestive system, predominantly in the large bowel, that impacts our health. Two key mechanisms have been proposed to underlie the health advantages of dietary fibre:

1. Fibre promotes gut motility by increasing stool volume and facilitating passage through the digestive tract. Microbial fermentation of dietary fibre by the human gut microbiome leads to an increase in bacterial mass and therefore faecal mass. Larger stool volume is associated with a reduced risk of colon cancer(12). Specific soluble fibres, such as beta glucan, also increase stool volume through the absorption and retention of water, resulting in the formation of a gel-like structure. This gel binds to excess cholesterol in the bowel and promotes excretion, lowering circulating cholesterol levels and therefore reducing risk of heart disease(13).

2. In addition, fibre has a prebiotic effect in the gut impacting the gut microbiotia. Prebiotic fibres such as inulin, galacto-oligosaccharides and fructo-oligosaccharides support the growth of healthy gut bacterial populations including bifidobacteria, lactobacilli and other short-chain fatty acid producing bacteria such as Faecalibacterium prausnitzii, whilst limiting growth of potential pathogens(14, 15). Short-chain fatty acids (SCFAs) produced by bacteria, specifically butyrate, acetate and propionate, support energy production, immunity and gut barrier function. In addition, SCFAs can alter the epigenome through metabolic regulatory receptors in organs throughout the body, reducing risk of diseases including obesity, diabetes, atherosclerosis, allergy, and cancer (16,17,18). In recent years more research has focused on the impact of dietary fibre on mental health, with some studies demonstrating a dose-dependent relationship between fibre intake and risk of depression(19). One study even found plant-based diets to protect against risk and severity of COVID 1920.

Why plant-based eating is key to meeting fibre recommendations and so much more

Fibre is found naturally exclusively in plant foods, and plant-based diets are therefore key to supporting increased fibre intakes at both an individual and population level.

‘Plant-based’ is a broad term to describe diets that are either predominantly or exclusively reliant on plant foods for energy and nutrients.

The term ‘plant-based’ can therefore encompass omnivorous, pescatarian, vegetarian and vegan dietary patterns that are high in whole plant foods such as beans, legumes, whole grains, fruits, vegetables, nuts, seeds and plant-based alternatives to dairy such as bean, nut and grain-based yogurt and milk alternatives.

Studies have found that diets characterised by high-quality plant-based foods and lower intakes of animal products (predominantly meat and meat products) may be beneficial for health, irrespective of established chronic disease risk factors and genetic predisposition(20, 21).

The widely studied Mediterranean diet is an example of a plant-based dietary pattern and has been associated with considerable benefits to health(22).

It is not just the increase in fibre that leads to positive health outcomes on plant-based dietary patterns. Additional beneficial components include a variety of vitamins, minerals and non-nutritive plant compounds such as antioxidants and bioactive compounds.

In addition to the health benefits, more plant-based diets are also shown to be advantageous in reducing the negative impact of our food system on greenhouse gas emissions, land use, water use, eutrophication and biodiversity.

Moving towards more plant-based foods therefore not only supports human health but provides an opportunity to substantially reduce our environmental footprint(23). Due to the wealth of evidence, plant-based dietary patterns are supported by a variety of national(24) and international dietary guidelines, and guidance from other health organisations such as the World Cancer Research Fund(25), the Eat Lancet Planetary Health Diet(26), and the World Health Organisation(27).

Helping people to change

Translating the science of fibre into practical recommendations that support behaviour change remains a challenge for health professionals. To meet fibre recommendations of at least 25g per day, intake on a population level will need to increase by 25-50%. Despite this significant disparity, it's important to note that even small increases in dietary fibre intakes yields health benefits, and therefore relatively minor and perhaps more realistic dietary changes remain of value.

Personal motivations will vary between individuals and populations, and therefore adapting the information provided appropriately will be supportive of behaviour change.

Communication that focuses on plant foods, rather than fibre itself, is also important in light of their advantages over isolated fibre supplements(28). Discussing foods, rather than single nutrients, provides more relatable and practical approach for dietary change.

Other barriers to go more plant-based may include concern over taste differences, fear of not reaching nutrient requirements and cooking skills.

Focusing on simple recipes utilising tasty ingredients and plant-based alternatives is key for a wide audience, and education and reassurance is required around the nutritional adequacy of plant-predominant diets.

A western-style diet that is low in fibre is of cultural and societal norm in many European countries and change is likely to be more successful when supported by unified strategies from government and industry(29).

Overcoming fear factor of gastro-intestinal symptoms

Some people, fear that increased dietary fibre can result in unwanted digestive side-effects including bloating, excess flatulence and a change in bowel habit. These symptoms that arise are due to increased fermentation of fibre in the large bowel. Increasing fibre gradually allows for the gut microbial populations to adapt.

Increased quantities of fibre also requires an increase in fluid intake to support digestive function. These recommendations are key when counselling patients and clients on moving to an increasingly plant-based diet.

For those with irritable bowel syndrome (IBS), a personalised approach is recommended. In some circumstances a diet that supports a reduction in fermentable carbohydrates known as oligo-, di-, mono-saccharides and polyols, also called the low FODMAP diet, may be of benefit, however this is only recommended with the support of a FODMAP-trained registered dietitian to ensure efficacy and safety(30).

Cost

Affordability is a key driver of dietary choices, and fibre consumption has been found to be inversely associated with socioeconomic status.

Results of the Low Income Diet and Nutrition Survey (LIDNS) found a positive association between level of education and intake of fruit and vegetables, and 36% of respondents reported they couldn’t afford to eat balanced meals(31).

It is vital not to overlook the inclusion of cost-effective solutions and budget recipes, as well as non-cooking-based strategies to support increased intakes of fibre and improved food quality in low-income populations.

How to achieve fibre recommendations

Example day meeting 30g of fibre

High-fibre meal ideas

Fibre boosters throughout the day

• Look for a high fibre breakfast cereal like those based on whole grains or oats

• Add plant based drink or plant based alternative to yoghurt to your breakfast (e.g. on cereals or with fruit)

• Add some extra crunch and sweetness to your porridge or cereal with nuts and dried fruit

• Add some spinach, tomato, mushrooms and beans to your next fry up

• Leave the skin on fruits, vegetables and potatoes where you can to save time and fibre

• Fancy a salt crunch? Switch from crisps to popcorn

• Switch from white bread to bread made with wholemeal flour

• Swap the chicken in your curry for chickpeas, or swap to half and half

• Keep a bag of frozen vegetables in your freezer to throw into any meal

• Throw extra beans into your next stew, soup or Bolognese

• Serve your sauce with wholemeal pasta instead of white

• Snack on fresh fruit with nuts or vegetable crudites and hummus

• Make the simple swap to brown rice instead of white

Factsheet

Download our fibre factsheet - a series of five infographics covering the fibre gap challenge, health benefits of fibre in the diet, and behaviour change tips.

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