The role of dietary fibre and prebiotics in the paediatric diet

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Important health benefits are attributed to adequate dietary fibre intake. However, most Canadians adults consume only half the recommend daily intake of dietary fibre. Studies on the fibre intake of Canadian children are lacking, but American data have suggested that the median fibre intake for 1- to 8-year-olds is also about half of recommended daily intake ^[1]. Health care providers are ideally situated to promote the early establishment of a diverse, fibre-rich diet. This practice point reviews fibre-related definitions, the physiological effects of intake, known health benefits, and strategies for achieving recommended intakes. While current knowledge of dietary fibre is based largely on adult studies, paediatric studies have been highlighted here whenever possible.  

Dietary fibres include non-digestible carbohydrates, such as cell wall components, oligo-saccharides (e.g., fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS)), and resistant starches ^[2][3]. Dietary fibres are fermented predominantly in the colon, producing short-chain fatty acids (SCFA) that are absorbed and metabolized. Dietary fibres have been sub-classified as water soluble or insoluble ^[4], and while both types of fibre are fermentable, the former are more completely fermented by micro-organisms in the gastrointestinal (GI) tract. “Prebiotic” refers to fermentable fibres that confer health benefits by stimulating the growth and activity of typically beneficial intestinal microbiota ^[5]. The most studied prebiotics include oligosaccharides such as inulin, FOS, and GOS.

Fibre, physiology, and health effects

The various physical properties of dietary fibre, such as water solubility, viscosity, and fermentability, cause a wide range of physiological effects ^[4][6] (Table 1). Viscous soluble fibres slow gastric emptying, prolong small intestinal transit, and soften stools, contributing to bowel motion regularity. Soluble fibres have hypocholesterolemic effects, and reduce postprandial glycemia and insulinemia. Insoluble fibres tend to increase stool bulk and shorten intestinal transit, promoting laxation. Several health benefits are mediated by the production of SCFA. For example, prebiotics contribute to a healthier intestinal microbiome by increasing Bifidobacteria and Lactobacilli, and by inhibiting the growth of pathogenic bacterial populations by reducing fecal pH via SCFA production ^[5]-[7]. Prebiotics influence immune system maturation and improve immunity by enhancing intestinal barrier function ^[5]. One SCFA, butyrate, is particularly beneficial, producing anti-inflammatory, anti-oxidant, and anti-carcinogenic effects in the colon ^[6].

LDL Low-density lipoprotein; Na Sodium

The industrialization of food production has resulted in lowering fibre intake, raising sugar and animal protein intakes, and reducing microbial diversity in the human GI microbiome. These effects can alter microbiome function and SCFA production, and thus cause a shift in the inflammatory milieu that is believed to be associated with the appearance of chronic inflammatory diseases ^[8].

Therapeutic applications of dietary fibre

The importance of fibre in maintaining bowel function and microbiome health are well known, but most studies of the therapeutic uses of dietary fibre in specific diseases have been conducted in adults ^[3][9]. A low fibre diet is an important risk factor for chronic constipation in children ^[10]-[12]. However, there is limited and conflicting evidence for treating constipation with dietary fibre ^[10,13]. Therapeutic recommendations for chronic functional constipation include a normal fluid and fiber intake, and the use of laxatives ^[13][14]. Long-term control is facilitated by adapting dietary practices to increase fibre intake, promote bowel regularity, and prevent relapse ^[11][14][15]. Increasing fibre intake in children with special health needs can be challenging but effective. The use of fibre-containing enteral formula in tube-fed children is well-tolerated and has been shown to increase bifidobacteria ^[16] and decrease laxative use ^[17].

Fibre intake is inversely associated with energy-dense dietary choices, increased levels of body fat ^[18] and developing metabolic syndrome ^[19]. Epidemiological data generally support the role of fibre in body weight regulation ^[2]. Early evidence suggests that low glycemic diets (i.e., diets rich in dietary fibre resulting in reduced post-prandial glucose and insulin levels) may positively influence weight control and metabolic response in children, adolescents, and young adults ^[20][21]. Systematic reviews of adult studies have found prebiotic consumption to be associated with subjective improvements in satiety and metabolic parameters ^[22] and in body weight reduction ^[23]. Two studies in children have suggested that prebiotics help to decrease body weight and subjective measures of appetite ^[24][25]. Further intervention studies are needed to establish a potential role for high-fibre diets and of specific fibre intakes in preventing and treating paediatric obesity. Two cross-sectional studies in children and adolescents have suggested that high-fibre intakes are associated with lower odds of having metabolic syndrome ^[19][26]. Paediatric obesity often persists into adulthood and preventing obesity is the single most important strategy for lowering future metabolic syndrome rates ^[18]. In obese adults, prebiotics can help to regulate postprandial glucose and insulin concentration ^[22][27], and in adults with type 2 diabetes, high fibre diets lower serum glucose levels and improve insulin sensitivity and glycemic control ^[3]. The effect of fibre on the risk for and management of type 2 diabetes mellitus in children has been understudied.

Decreased intestinal microbiome diversity has been associated with functional paediatric GI disorders, such as colic and irritable bowel syndrome ^[4]. However, evidence for causality is lacking and effective interventions for prevention or treatment will require more focused research.

Are any risks associated with increasing dietary fibre intake?

In vitro studies have suggested that a high-fibre diet may negatively impact intestinal mineral bioavailability (e.g., calcium, zinc, and iron). However, this concern is not well supported by in vivo studies. Decreased mineral absorption may occur due to mineral binding or physical entrapment in the small bowel, but subsequent colonic fermentation may liberate minerals and enhance their absorption ^[28]. Mineral status may be more concerning in children who consume mineral-deficient diets and/or with GI conditions that compromise absorptive capacity ^[1]. Further research, including mineral balance studies of high-fibre foods and bioavailabilty, are needed.

Studies from 40 to 50 years ago in vegetarian and/or vegan children raised concerns about growth delay associated with high fibre intake. Lower dietary protein intake may have been a confounding factor in many of these studies, however ^[29][30]. The impact of high fibre intake on growth has not been well studied, but growth should be monitored closely in children on strict vegan diets ^[31]. When assessing a child with poor weight gain, the possibility that inadequate protein intake and low caloric density is associated with a ‘bulky’ high fibre intake should always be considered. In Canada, where fibre intake is suboptimal for about half the population, increasing fibre to ranges recommended in Canada’s latest food guide are unlikely to affect growth or mineral status adversely.

Encouraging fibre-rich diets for parents and children

American data have suggested that the median fibre intake for 1- to 3-year-olds is 10 g /day, and 13 g /day for 4- to 8-year-olds ^[1]. Canadian recommendations have been extrapolated from adult data and are based on an adequate intake (AI) of fibre of 14 g /1000 kcal for all age groups over one year ^[32] (Table 2).

Children whose diets focus on low fibre-containing foods should be encouraged to consume some foods that are high in fibre (>4 g/serving is considered high and >6 g/serving very high).

Whole foods contain different proportions of soluble and insoluble fibres. Legumes (e.g., lentils, chickpeas, beans) are high in total, soluble, and insoluble fibre, and are also a rich source of protein, iron, and folic acid. Psyllium and some isolated fibres, such as pectin, guar gum or inulin, are high in soluble fibres, while wheat bran, for example, is high in insoluble fibres. Plant-based foods containing prebiotics, such as FOS and inulin, include onions, garlic, leeks, banana, chicory, asparagus, wheat, and some cereals. Aiming for a diverse diet will facilitate the inclusion of a variety of fibre types and thus the spectrum of physiologic benefits. Counselling families to diversify their diet can include reviewing which foods contain more or less fibre—some foods can be surprising. Rather than focusing on “gram counting”, discussing healthier choices with parents and children should raise awareness of the physiological benefits of eating a variety of fibre-rich foods (Table 3)^[33]-[35].

Some parents and health professionals still believe that children will refuse to eat high fibre foods. In many parts of the world, children consume fibre-rich diets much earlier (and more enthusiastically) than in Canada. Studies have demonstrated the acceptability of dietary fibre ^[15][34]. While it is true that some high-fibre cereals, fresh fruits, and vegetables are relatively expensive, and availability can be a challenge in remote or disadvantaged communities, legumes are an inexpensive source of fibre and plant-based protein. Increasing legumes in the family diet is a low-cost high-yield nutritional change. Many families can benefit from information on legume preparation, cooking, and creative inclusion into meals. There are quality online resources that promote fibre intake. In Canada, there is great opportunity to diversify family diets by experiencing and incorporating foods and dishes from traditional Asian, Indian, Mediterranean, and Middle Eastern cuisines.

Acknowledgements

This practice point was reviewed by the Canadian Paediatric Society’s Community Paediatrics Committee.

CANADIAN PAEDIATRIC SOCIETY NUTRITION AND GASTROENTEROLOGY COMMITTEE
Members: Linda M. Casey MD, Eddy Lau MD (Board Representative), Catherine M. Pound MD (Chair), Ana M. Sant’Anna MD, Pushpa Sathya MD, Christopher Tomlinson MB, ChB, PhD
Liaisons: Becky Blair MSc RD, Dietitians of Canada; Patricia D’Onghia MPH RD, Health Canada; Tanis R. Fenton PHD RD, Dietitians of Canada; Laura Haiek, Breastfeeding Committee for Canada; Deborah Hayward, Bureau of Nutritional Sciences, Health Canada; Sarah Lawrence MD, Canadian Pediatric Endocrine Group
Principal author: Dana Boctor MD

References

Disclaimer: The recommendations in this position statement do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. Internet addresses are current at time of publication.