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Fibre: the true health provider

Victoria J Burley
PhD
Principal Research Fellow
University of Leeds

Since the concept of dietary fibre was developed more than 60 years ago, the question of how much is needed for good health has continued to tax nutrition scientists. This article examines the health benefits of a high-fibre diet.

Dietary fibre is found in all plant foods, especially bran-based and some whole grain breakfast cereals, grains, breads, fruit, vegetables, legumes, lentils, nuts and seeds. Most foods high in fibre are low in fat and are rich sources of other nutrients, making them an important part of a balanced diet. Dietary fibre may be broadly separated into water-soluble fibre (which forms a gel helping with satiety, cholesterol and blood glucose control) and water-insoluble fibre (which can also support satiety and regulating bowel function). 

Since the concept of dietary fibre was developed more than 60 years ago, the question of how much is needed for good health has continued to tax nutrition scientists. Lack of consensus has been caused partly by uncertainties in the definition of the term dietary fibre,1 and partly by the various methods for dietary fibre analysis.

Globally, a number of different methodologies have been used to measure dietary fibre, with the Englyst and the Association of Analytical Chemists (AOAC) methods being the most common. The Englyst method measures only the non-starch polysaccharides (NSP) fraction, eg, cellulose, while the AOAC method also includes beneficial oligosaccharides, lignin and resistant starch, with the effect that AOAC values tend to be on average about 35% higher. While reference food tables in the UK report NSP, actual food labelling requirements use the AOAC method. The dietary reference value (DRV) for NSP recommends an adult intake of at least 18 g per day; however, to maintain a DRV in line with AOAC food fibre values, the GDA (guideline daily amount) is 25 g per day.

One thing is clear - fibre is a true nutritional deficiency within the UK, with National Diet and Nutrition Survey (NDNS) data illustrating that as many as eight in 10 adults and children are not getting enough.2,3 The significant contributors in the diet include wholemeal breads (6%), fruit and nuts (9-10%), vegetables (20%) high-fibre and some whole grain breakfast cereals (11%). People who eat high-fibre cereals are up to 80% more likely to achieve recommended fibre intakes.3

The original concept of dietary fibre as "roughage" was related mainly to faecal bulking,4 and the laxative effects of dietary fibre are now well documented. Cereal fibres are the most effective way to increase bulk and shorten transit time in the digestive tract, helping to avoid constipation. However, the health benefits of dietary fibre go beyond just digestive health. Several reviews have indicated that dietary fibre may help prevent weight gain.5-7

Further supportive evidence comes from a recent study, which found that women who increased their fibre intake over two years increased their likelihood of losing weight and those who decreased their intake were more likely to gain weight.8

Therefore, encouraging greater fibre intake is a key part of weight management strategies. High-fibre foods tend to be bulky with low energy density. This means they can take longer to chew, which may slow down eating rate and permit the brain to register the sensation of satiety before over-eating can occur. Soluble types of fibre may also prolong gastrointestinal transit time, slow glucose absorption and reduce blood glucose excursions, which stimulate hunger.6

Bowel cancer is the second highest cause of cancer death in  the UK, and is responsible for 16,170 deaths each year; consequently, even small effects on risk can have an impact on many people. The European Prospective Investigation into Cancer and Nutrition (EPIC) found that people eating low-fibre diets could dramatically reduce their risk of bowel cancer simply by eating more fibre rich foods.9 In weighing up all of the evidence, the World Cancer Research Fund concluded that foods containing dietary fibre probably protect against colorectal cancer.10

High-fibre diets can also play a role in improving cardiometabolic health. A large US study has shown that for every 10 g/day increase in fibre consumption by people with initially low intakes, the risk of heart disease can fall by 14%,11 and a Cochrane Systematic Review of evidence in 2008 found that people who regularly eat high-fibre diets are one-third less likely to develop diabetes than people who eat diets that contain few fibre-rich foods.12 

Epidemiological studies have also indicated that high fibre and  whole grain intake is protective against cancer, CVD, diabetes, and obesity.10,13-15 But, the definition of whole grains used within scientific studies varies widely and a consistent definition has not been applied. The cardiovascular health benefits of whole grain are supported only where whole grain definitions use foods containing significant fibre or bran. This is confirmed by new research conducted by the Life Sciences Research Institute Inc (www.LSRO.org).13 Using a panel of independent scientists, their extensive review strongly supports the view that dietary fibre is in fact the power-house within whole grain foods, driving beneficial effects for cardiovascular health. Therefore, fibre should be a consistent factor when assessing and communicating the benefits of whole grain and grain-based foods.

References
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