Dietary fibers (DF) - non-digestible plant polysaccharides - have been shown to have important effects on human health, including preventing and alleviating constipation, reducing gastrointestinal cancer incidence and blood glucose levels, lowering blood cholesterol levels and blood pressure, and beneficially modulating gut microbiota. Yet most official food composition tables and food questionnaires do not provide enough data to assess fermentable DF.
A team of researchers therefore aimed to develop a new database and a food frequency questionnaire (FFQ) allowing detailed DF intake estimation including: soluble DF, insoluble DF and prebiotic (oligo)saccharides (inulin-type fructans, fructo-oligosaccharides and galacto-oligosaccharides).
In their report, published in Nutrients, they explain their development is a 12 month FiberTAG FFQ using a single frequency scale with six categories from ‘never’ to ‘more than once a day’. It consists three DF-containing food groups (vegetables, fruits, cereal products), subdivided into 18 subcategories and considers ‘bread/pastries/cookies/cereal breakfast/rice/pasta’ for cereal products as well as ‘raw/fresh’, ‘cooked’, ‘juice’, ‘spreadable’ or ‘tinned’ for vegetables or fruits.
A fourth section named “others” details condiments, chocolate, cooked meals, dairy products and beverages containing DF which account for DF in typical French and Belgian diets, due to that fact these were the two countries where the questionnaire's use was first intend.
These elements result in a FFQ that includes 302 food items. The question of seasonal consumption was also addressed for some vegetables and fruits.
Portion size was estimated using photographs from the published Belgian booklet (“Outil pour estimer la consommation alimentaire”, CIRIHA). An annex of this photobook was created for missing specific products. Space for comments were left at the end of each food subcategories. The time required to complete this FFQ was around one hour.
To test the efficacy of the questionnaire, the researchers recruited 15 healthy students. Subjects were asked to complete the FiberTAG FFQ. Detailed verbal and written instructions were provided by a dietician. An Excel tool was created from the FiberTAG repertoire and DF contents, including fructans, FOS, GOS, were calculated in all food products including composite foods and cooked meals (pastries, breads, etc.) by using food composition from classic recipes.
The daily intake of different types of DF over the 12 month period was then calculated, taking into account frequency, portion size and seasonal consumption. Mean and median (with minimum and maximum) values of DF intake were calculated for each DF types and for each subject since there were sometimes up to three values for some types of DF depending on the sources mentioned in the new repertoire.
The resulting data show a total DF intake of 38 g/day in the tested population. Vegetables was the largest contributor to total DF intake. Cereal products, and more specifically flour-based products, arrived in second position. Then, the fruit category, most often consumed as fresh fruits, contributed to 21% of total DF intake. Major food sources of naturally occurring ITF in Belgian diets were condiments (principally onions and garlic) which provided about 43%, whereas condiments and flour-based products provided each one third of daily FOS intake. Cooked vegetables were the major source of GOS daily consumption.
The report's authors note that an intake of 38g/day is higher than the estimated contribution for the average Belgian in the 2014–2015 Food Consumption Survey (18 g/day) and higher compared to previously reported intake for adults in Europe ranging from 16 to 24 g/day based on 24 h-recall or 3–7 days records. In fact, 38 g/day is closer to the European (EFSA) and Belgian (CSS) recommendations, which ranges from a minimum of 25 g to ideally 30 g of fiber per day, in order to have significant health benefits.
The authors suggest this difference might be explained by a "more adequate inclusion of fruits and vegetables intake in FFQ than with other methods, as previously reported".
The report concludes that the FiberTAG repertoire and FFQ are major tools for the evaluation of the total amount of DF including prebiotics. Their use can be helpful in intervention or observational studies devoted to analyse microbiota–nutrient interactions in different pathological contexts, as well as to revisit DF intake recommendations as part of healthy lifestyles considering specific DF.
The FFQ used in the study is applicable for the Belgian adult population but might also be relevant for adult populations in other European countries with similar food patterns, in particular neighbouring countries (Germany, France, Luxembourg, The Netherlands).
As prebiotics are now used as functional ingredients in yogurts and breakfast cereals, the formulation, use and availability of such food products vary between different countries so those wishing to use the FiberTAG FFQ should first identify this kind of fortified food products and record their intake to ensure accurate assessment of prebiotic (oligo)saccharides intakes.
The report notes knowledge gaps which could be addressed in future studies: "An exhaustive literature search has been performed to deeply complete the database with prebiotic (oligo)saccharide levels (ITF, FOS, GOS) in food products using published scientific data. However, even though we found values of total DF for most of the food items, this repertoire highlighted several gaps for some categories of fiber (mostly FOS and GOS) and encouraged further additional analysis of prebiotic (oligo)saccharides."
Delzenne. N. M., et al
"Development of a Repertoire and a Food Frequency Questionnaire for Estimating Dietary Fiber Intake Considering Prebiotics: Input from the FiberTAG Project"