Fibre: The Forgotten Carbohydrate in Sports Nutrition Recommendations

Abstract

Although dietary guidelines concerning carbohydrate intake for athletes are well established, these do not include recommendations for daily fibre intake. However, there are many scenarios in sports nutrition in which common practice involves the manipulation of fibre intake to address gastrointestinal comfort around exercise, or acute or chronic goals around the management of body mass or composition. The effect of fibre intake in overall health is also important, particularly in combination with other dietary considerations such as the elevated protein requirements in this population. An athlete's habitual intake of dietary fibre should be assessed. If less than 20 g a day, athletes may consider dietary interventions to gradually increase intake. It is proposed that a ramp phase is adopted to gradually increase fibre ingestion to ~ 30 g of fibre a day (which includes ~ 2 g of beta-glucan) over a duration of 6 weeks. The outcomes of achieving a daily fibre intake are to help preserve athlete gut microbiome diversity and stability, intestinal barrier function as well as the downstream effects of short-chain fatty acids produced following the fermentation of microbiome accessible carbohydrates. Nevertheless, there are scenarios in which daily manipulation of fibre intake, either to reduce or increase intake, may be valuable in assisting the athlete to maintain gastrointestinal comfort during exercise or to contribute to body mass/composition goals. Although further research is required, the aim of this current opinion paper is to ensure that fibre is not forgotten as a nutrient in the athlete's diet.

Fig. 1

Dietary fibre classification based on molecular weight. Categories of the different types of non-digestible carbohydrates according to molecular weight. Non-starch polysaccharides, resistant starches (RS) [types 1–5] and lignin are high-molecular-weight dietary fibres. Resistant oligosaccharides (including short-chain inulin degree of polymerisation [DP] ≤ 10, as fructooligosaccharides and oligofructose) and natural inulin (DP value in range 2–60) are low molecular weight. Fructooligosaccharides and galactooligosaccharides are considered as well as Fermentable Oligosaccharides, Disaccharides and Monosaccharides and Polyols (FODMAP) compounds and included within the FODMAP group

Fig. 2

Fermentation capacity of dietary fibre and associated positive (+ ive) and negative (− ive) impact of the athlete’s gut. GI gastrointestinal, IBS irritable bowel syndrome, SCFAs short-chain fatty acids

Fig. 3

Guideline of increasing dietary fibre intake in athletes. Practical theoretical framework for athletes to achieve dietary fibre intakes. General fibre recommended daily amount quantities for men and women are used [96]. Top: a schematic aimed at achieving adequate dietary fibre ingestion. Following an initial evaluation of dietary fibre intake (ASA 24 h) and gastrointestinal symptoms (Gastrointestinal Symptom Rating Scale [GSRS]), a 4-week “ramp phase” period is recommended. Athletes should gradually increase the intake of fibres from ~ 20 to ~ 30 g with the aim of adding at least 10 g of fibre to their baseline consumption followed by a 2-week “maintenance phase”. Middle: a daily distribution of dietary fibre according to the main meals. Each main meal includes by ~ 7 g of fibre, while a snack throughout the day contains ~ 3 g. Daily adequate intakes of dietary fibres (microbiota accessible carbohydrates [MACs]) provide benefits for gastrointestinal health and gut microbiota composition and function (production of short-chain fatty acids [SCFAs]. Bottom: general recommendations for fibre management around exercise training and competition