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The fibre gap: The importance of dietary fibre for health
Professionals from all sectors of the food, nutrition and health space have been urging consumers for decades to include more fibre in their diet.
Despite all the attention and buzz around healthy food in general, and fibre in particular, most consumers fall short in including enough fibre in their diets.
Although there is growing evidence for the need to increase our fibre intake, and a considerable consumer awareness around the importance of dietary fibre, only a relatively small proportion of consumers eat the recommended amount of daily fibre and a ‘fibre gap’ persists.1 This is concerning for health experts in clinical practice, public health, and academic realms and even the World Health Organization (WHO).
Intake and recommendations
Dietary fibre is included in nutrition guidelines because of its positive health effects. The guidelines for dietary fibre intake vary across European countries and range from 25 to 40g per day for adults. The British Government, French Agency for Food, Environmental and Occupational Health & Safety, and the German Nutrition Society recommend a daily intake of 30g per day. European Food Safety Authority (EFSA) recommends ingesting 25g of fibre each day.
However, on average, intakes for adult men in Europe range from 18 to 24g per day and from 16 to 20g per dday for women, with little variation from one European country to another and all below the recommended daily intakes.
The Dietary Guidelines for Americans, written by the US Department of Agriculture and the US Department of Health and Human Services, recommend 14g per day of fibre for every 1000 kcal ingested. This translates to 28g per day for adults. Americans also consume too little fibre, typically about half (15g) of the recommended daily amount. There is a serious fibre gap in the Western world.
Reaching the daily recommended intake would require a substantial change in dietary habits for many individuals. For example: 5 grams of fibre equals 12 spoons of rice, three apples, or two slices of wholemeal bread. Increasing dietary fibre consumption provides an opportunity to lower the overall caloric intake while providing additional health effects such as lowering blood glucose levels and supporting cardiovascular health.
Types of fibre
Dietary fibre is the collective term for non-digestible carbohydrates that are not degraded by the digestive enzymes in the human small intestine. As they are not immediately digested, they reach the colon relatively intact, where some of them, namely soluble fibre, are partially or completely fermented by microbiota indigenous to the colon.
This results in a wide range of health benefits, including improved gut barrier function and microbiota composition, both of which have positive health implications across digestive health, general bowel function, immune system function, hormonal regulation, and heart health.
Dietary fibre can be either soluble or insoluble, both of which are important for maintaining good digestive health. However, each has different properties and effects on the body.
Insoluble fibre
Insoluble fibre does not dissolve in water and remain relatively unchanged (little or no fermentation) as they pass through the digestive system. Insoluble fibre helps to add bulk to the stool and promote regular bowel movements, which can help prevent constipation and other digestive problems. Insoluble fibre also provides a feeling of fullness, which can help with weight management. This type of fibre is found in foods such as wheat bran, whole grains, nuts and vegetables.
Soluble fibre
Soluble fibre dissolves in water, forming a gel-like substance which slows down digestion. Furthermore, soluble fibre may be fermented; the human colonic microbiota use fibre as energy source while generating microbial biomass, short chain fatty acids (SCFAs) and gases; much of the SCFAs and gases are absorbed and utilized by the human body to maintain health. Some bacteria are able to use SCFAs as a source of energy for their growth. This type of fibre is found in foods such as oat bran, beans, peas, lentils, apples, and citrus fruits. Some soluble fibre, like inulin and oligofructose, also has a prebiotic effect. This means it is fermented by a selective group of microbiota and are associated with certain health benefits.
Benefits of fibre
The benefits of dietary fibre are well studied. One of the most important effects is its effect on stools: fibre decreases the time for food to pass through the gastrointestinal tract and increase fecal bulk. Fibre also contributes to satiety and lower blood glucose response. In the long term, fibre is associated with a decreased risk of cardiovascular diseases, type 2 diabetes and colon cancer.2,3,4,5
Research is increasingly showing how important the bacteria in our gut are for our health.6,7 We all have millions of bacteria in our gut, also called microbiota. There are numerous species of bacteria and these can be beneficial or harmful for our health. The balance of these ‘good’ and ‘bad’ bacteria can be affected by several factors, including diet and lifestyle.
For example, soluble fibre such as inulin, fructooligosaccharides (FOS) and galactooligosaccharides (GOS) is fermented by Bifidobacteria and Lactobacilli. These beneficial bacteria increase while they ferment soluble fibre and they produce SCFAs, which are associated with health benefits. This is the so-called prebiotic effect. Furthermore, a good balance of beneficial bacteria in the gut is related to improved gut health, immunity, and possibly even brain function.
Fibre enrichment of food products
More and more consumers are aware that they need to increase their fibre intake to fill the gap between the recommended daily intake and their actual intake. Most might find it difficult to do this by increasing food products that are well known for their high fibre content, like fruit, vegetables and wholemeal products. For this group of consumers, food products with added fibre will provide a convenient and easier way to increase their fibre intake.
Depending on the type of food, adding fibre to the recipe might be challenging to develop final products with a pleasing taste and texture. Insoluble fibre provides physical particles often with high-water binding capacity. This might help to stabilize the food products, but when (too) high levels are added it can negatively affect the texture and mouthfeel. Soluble fibre, on the other hand, does not have the disadvantage of introducing physical particles into the formulation.
Some soluble fibre has additional benefits for food applications as well. For example, chicory root fibre, with its slightly sweet taste, can act as a sugar replacer as well as increasing the amount of fibre. Depending on the type of food application, the best choice of insoluble fibre, soluble fibre or even a combination of both can be made. The choice can be based on the technological functionalities of increasing fibre, as described, but also on additional nutritional benefits such as sugar and/or fat reduction.
Conclusion
Although consumers know that fibre is important for digestive and overall health, the fibre gap persists. This brings opportunities for food manufacturers to develop added-fibre products to create a more convenient and easier way for consumers to increase their fibre intake. Adding certain fibre will even introduce additional benefits, for example, in terms of flavour and texture and their potential to reduce sugar.
References
1. Jones, JM. CODEX-aligned dietary fiber definitions help to bridge the ‘fiber gap’. Nutr J 13, 34 (2014).
2. Anderson JW.; Baird P.; Davis RH.; et al. (2009) Health benefits of dietary fiber. Nutr Rev 67, 188–205.
3. Bingham SA.; Day NE.; Luben R.; et al.(2003) Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet 361, 1496–1501.
4. Kim Y and Je Y. (2014) Dietary fiber intake and total mortality: a meta-analysis of prospective cohort studies. Am J Epidemiol 180, 565–573.
5. Threapleton DE.; Greenwood DC.; Evans CE.; et al. (2013) Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ 347, f6879.
6. Hadrich D. Microbiome Research Is Becoming the Key to Better Understanding Health and Nutrition. Front Genet. 2018 Jun 13;9:212. doi: 10.3389/fgene.2018.00212.
7. Gilbert JA.; Blaser MJ.; Caporaso JG.; et al. Current understanding of the human microbiome. Nat Med. 2018 Apr 10;24(4):392-400. doi: 10.1038/nm.4517.