Original ResearchKnowledge about sources of dietary fibres and health effects using a validated scale: a cross-country study
Introduction
Dietary fibre (DF) is a broad category of non-digestible food ingredients originating from plant materials that includes non-starch polysaccharides, oligosaccharides, lignin, and analogous polysaccharides.1, 2, 3
The most widely spread classification of DF some years ago was related to its solubility in water. However, other classifications are presently accepted and include microbial fermentation in the large intestine as well as viscosity, since these have shown to greatly influence the physiologic effects of DF.4, 5 Cellulose, hemicellulose and lignin are the structural parts of plant materials and belong to the category of insoluble fibre because they do not dissolve in water and are not metabolized by intestinal bacteria. On the other hand, pectins, gums and polysaccharides exist within and around the plant cells and belong to the category of soluble fibre since they are water soluble (acquiring a gel-like structure) and fermentable by colonic bacteria.1, 2
However, the definition of DF has extended to include oligosaccharides with properties similar to soluble DF and resistant starches that escape enzymatic digestion in the small intestine and, hence, act as DF in the large intestine.6 Contrarily to common DF, prebiotic DF is not classified in terms of solubility or viscosity, being defined in terms of resistance to digestion and absorption in the small intestine, partial or complete fermentation by microbiota in the large intestine, and the ability to stimulate growth of select bacteria.2, 7 Inulin and transgalactooligosaccharides fill the three criteria mentioned, and hence are considered prebiotics. According to Roberfroid et al.8 in the future other oligosaccharides and polydextrose may also come to be classified as prebiotics.
A very significant number of scientific studies confirm the important role of DF consumption in reducing many diseases like cancer, diabetes, obesity and coronary heath diseases.9, 10 According to Huang et al.11 and based on several recent meta-analyses including a large number of subjects and prospective studies, a high intake of whole grains and cereal fibre showed significant and consistent protective effects on diseases such as type 2 diabetes, cardiovascular disease and certain cancers (e.g. colorectal cancer).
A study by Threapleton et al.12 investigated the intake of DF and any potential dose–response associations both with coronary heart disease and cardiovascular disease, and concluded that DF consumption is in fact associated with a lower risk of both diseases.
Yokoyama et al.13 conducted a systematic review and meta-analysis of controlled clinical trials and observational studies that have focused on the association between vegetarian diets, composed of fibre rich foods, and blood pressure, and they concluded that consumption of vegetarian diets is associated with lower blood pressure, and hence could constitute a useful non-pharmacologic approach for this problem.
Murphy et al.14 studied the DF intake and the risks of cancers of the colon and rectum, along a period of 11 years and considering 4517 documented cases of colorectal cancer. They observed that total DF was inversely associated with colorectal cancer, as well as with colon and rectal cancers. Furthermore, the association between total DF and risk of colorectal cancer risk did not differ by age, by sex, or by anthropometric, lifestyle and dietary variables. Still they observed that while both fibre from cereals and fibre from fruits and vegetables were similarly associated with colon cancer; for rectal cancer, the inverse association was only evident for fibre from cereals.
Encarnação et al.15 highlights the role of DF in lowering the risk of developing colorectal cancer through the fermentation of the DF by intestinal microbiota, which produces butyrate, which in turn has been reported as a chemopreventive agent. Furthermore, they reviewed recent new insights that focus on butyrate role not only in preventing colorectal cancer but also in treating it. Similar reports were made by Bordano and Lazarova16 and by Le Leu et al.17
According to Norat et al.18 there is evidence that high intakes of fruits and vegetables may reduce the risk of cancers of the aerodigestive tract.
Constipation is a common, often chronic, condition that is a health concern for providers of care. The regular consumption of DF, together with the ingestion of fluids and exercise constitute a first-line treatment of constipation.19, 20 Tabbers and Benninga21 conducted a systematic review to investigate constipation in children, including 12 studies. They present evidence of the effectiveness and safety of two interventions in particular, which are the use of DF and probiotics. DF supplements have been reported as useful for the management of chronic constipation and irritable bowel syndrome.22
Insulin resistance syndrome, especially with diabetes, is becoming increasingly prevalent worldwide, due to increased consumption of low-fibre and refined-carbohydrate diets.23 The study by Balk et al.24 studied the association of diet and lifestyle with glycated haemoglobin in type 1 diabetes. A 7-year prospective cohort analysis was performed in 1659 patients participating in the EURODIAB Prospective Complications Study, and the results obtained suggest that low intake of vegetable protein and DF is associated with worse glycaemic control in type 1 diabetes.
Seal and Brownlee25 report an increasing evidence, based both on observational and intervention studies, that increased intake of less-refined, whole-grain foods has positive health benefits, among which stand type 2 diabetes. The InterAct Consortium study on DF and incidence of type 2 diabetes in eight European countries followed 11,559 participants with type 2 diabetes along 10.8 years. The results of the study evidence that the intake of total and cereal fibre is inversely related to the risk of type 2 diabetes.26
Whincup and Donin27 highlight diet and nutrition as being strongly implicated in the aetiology of type 2 diabetes, and report specially low DF intake as an important factor. Furthermore, the authors demonstrate the diet patterns associated with the low intake of DF. In fact, prospective observational studies show that there appears to be low cereal fibre intake, rather than low fruit and vegetable fibre intake. The results presented strengthen the evidence implicating cereal fibre as an important determinant of type 2 diabetes risk and suggest that randomized controlled trials aimed at examining the effect of cereal fibre supplementation on type 2 diabetes risk should be conducted.
Although DF is a theme thoroughly investigated in terms of their quantification, analysis and their effects on the human being, little is known about the perceptions of people about DF or their levels of knowledge. Hence a study was conducted by Guiné et al.28 aimed to develop and validate an instrument to evaluate the knowledge of the general population about DFs. In that study, a group of questions were evaluated and two factors resulted from the structural equation modelling (SEM) applied: one related to dietary fibre and promotion of health (DFPH) and the other related to sources of dietary fibre (SDF).
The aim of the present work was to use the validated scale developed by Guiné et al.28 to assess the knowledge about dietary fibre (KADF) in terms of the two variables defined (sources and effects on human health) so as to evaluate the relations between some sociodemographic variables such as age, gender, level of education, living environment or country on the levels of knowledge.
Section snippets
Data collection
The methodological study of psychometric validation was conducted by means of a questionnaire survey, applied in 10 different countries situated in different parts of the globe for the evaluation of geographical influence on the level of KADF, among other factors. Hence the participants resided in several countries from different continents (Europe, America, Africa), which integrated a project of the CI&DETS Research Centre (IPV, Viseu, Portugal).
The participation in the survey was voluntary,
Sample characterization
The methodological study of psychometric validation was conducted with 6010 participants, from which 65.7% were female and 34.3% male, aged between 17 and 84 years, with an average age of 34.5 years (±13.74 SD), distributed as follows: one third stand in the class from 17 to 24 years, inclusive; another third stand in the class from 25 to 40 years, inclusive; and finally the last third stands in the class from 41 to 84 years, inclusive.
The participants resided in 10 countries from three
Discussion
This study used a validated tool, KADF, previously developed by the authors28 and validated by SEM. This scale included eight validated questions, four in each of two factors: SDF and DFPH. This model was, therefore, the basis for the present work, which evaluated the knowledge about DF in a global way and also regarding each of the factors, based on the questions that composed each of them. Furthermore, the differences were evaluated between groups, considering several sociodemographic
Acknowledgements
This work was prepared in the ambit of the multinational project from CI&DETS Research Centre (IPV, Viseu, Portugal) with reference PROJ/CI&DETS/2014/0001.
Ethical approval
No ethical approval was necessary for undertaking the present work, by means of questionnaire. The participation in the survey was voluntary, and done only to adult citizens. Verbal informed consent was obtained from all participants and it was ensured that the data provided were kept strictly confidential.
Funding
None declared.
Competing interests
None declared.
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