Dietary fibres are indigestible parts of plants that are incredibly important for intestinal health. But did you know that these plant fibres have a role to play outside of your gut too? Our gut bacteria can transform fibres into potent signalling molecules that can potentially delay the aging of the brain. Pretty clever, right?

Fibre-digesting gut bacteria produce short-chain fatty acids

As humans cannot digest dietary fibres, they enter your large intestine typically intact. Here they are eagerly anticipated by a hungry bunch of bacteria. As your gut bacteria feast on the fibre they start to produce short-chain fatty acids (SCFAs) – the main ones being acetate, propionate and butyrate (1-3).

Unlike fibre, your body can actually absorb and use these SCFAs. They provide energy for the body (which would otherwise remain inaccessible) delivering 2 kcal per gram of fibre and about 5-10% of daily energy needs. SCFAs positively affect intestinal physiology in many other ways; in fact, they are now considered to underlie many of the long-recognized benefits of high-fibre diets (1, 4-6) .

SCFAs impact the brain via various routes and in various ways

Interestingly, SCFAs are thought to play a key role in the gut/ brain connection by triggering the nerves in your gut, enabling it to ‘talk’ to the brain directly. SCFAs can also reach your brain via your blood, where they can support with reducing inflammation, aiding the growth and repair of brain tissue, and controlling levels of serotonin and other neurotransmitters (important messenger molecules within the central nervous system) (2, 3, 7, 8).

In addition, SCFAs can indirectly interact with immune cells, and also potentially impact on emotion, cognition and even mental disorders. And these hero fatty acids can also trigger the secretion of gut hormones and neurotransmitters that regulate satiety and food intake as well as learning, memory and mood (3, 9, 10).

Food for thought – how to boost your production of SCFAs

Now you know how powerful SCFA’s can be – it’s time to turn to an effective strategy to boost your body’s production of them! One big step forward is to eat more fibre-rich foods such as fruits, vegetables, nuts and cereals (11, 12). For normal intestinal function you should aim for at least 25g of fibre per day (4) but some experts think you may need to double that amount to reap the full health benefits of SCFAs (13). You can also take supplements that provide live and beneficial bacteria or yeast (known as probiotics) and/or specific dietary fibres, that feed these friendly bacteria in your gut (known as prebiotics) (14-16).

Despite research into SCFAs and their impact on brain health being in its infancy (3), a fibre-rich diet is inevitably good for all of us – providing a sound return for our health and wellbeing that goes way beyond the lining of our guts.

References

1. Gentile CL, Weir TL. The gut microbiota at the intersection of diet and human health. Science. 2018;362(6416):776-80.
2. Cryan JF, O'Riordan KJ, Cowan CSM, Sandhu KV, Bastiaanssen TFS, Boehme M, et al. The Microbiota-Gut-Brain Axis. Physiol Rev. 2019;99(4):1877-2013.
3. Dalile B, Van Oudenhove L, Vervliet B, Verbeke K. The role of short-chain fatty acids in microbiota-gut-brain communication. Nat Rev Gastroenterol Hepatol. 2019;16(8):461-78.
4. EFSA Panel on Dietetic Products N, Allergies. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre. EFSA Journal. 2010;8(3):1462.
5. Blaak EE, Canfora EE, Theis S, Frost G, Groen AK, Mithieux G, et al. Short chain fatty acids in human gut and metabolic health. Benef Microbes. 2020;11(5):411-55.
6. Roager HM, Dragsted LO. Diet-derived microbial metabolites in health and disease. Nutrition Bulletin. 2019;44(3):216-27.
7. Schächtle MA, Rosshart SP. The Microbiota-Gut-Brain Axis in Health and Disease and Its Implications for Translational Research. Front Cell Neurosci. 2021;15:698172.
8. Banerjee S, McCracken S, Hossain MF, Slaughter G. Electrochemical Detection of Neurotransmitters. Biosensors (Basel). 2020;10(8).
9. Romaní-Pérez M, Bullich-Vilarrubias C, López-Almela I, Liébana-García R, Olivares M, Sanz Y. The Microbiota and the Gut-Brain Axis in Controlling Food Intake and Energy Homeostasis. Int J Mol Sci. 2021;22(11).
10. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25.
11. Bolte LA, Vich Vila A, Imhann F, Collij V, Gacesa R, Peters V, et al. Long-term dietary patterns are associated with pro-inflammatory and anti-inflammatory features of the gut microbiome. Gut. 2021;70(7):1287-98.
12. Koponen KK, Salosensaari A, Ruuskanen MO, Havulinna AS, Männistö S, Jousilahti P, et al. Associations of healthy food choices with gut microbiota profiles. Am J Clin Nutr. 2021;114(2):605-16.
13. Makki K, Deehan EC, Walter J, Bäckhed F. The Impact of Dietary Fiber on Gut Microbiota in Host Health and Disease. Cell Host Microbe. 2018;23(6):705-15.
14. Sandhu KV, Sherwin E, Schellekens H, Stanton C, Dinan TG, Cryan JF. Feeding the microbiota-gut-brain axis: diet, microbiome, and neuropsychiatry. Transl Res. 2017;179:223-44.
15. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014;11(8):506-14.
16. Gibson GR, Hutkins R, Sanders ME, Prescott SL, Reimer RA, Salminen SJ, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol. 2017;14(8):491-502.