The fibre story we’ve been told is incomplete. For years, we’ve been told a simple message in articles, books and social media: eat more fibre. While that advice isn’t wrong, it misses something very important. Fibre isn’t just a number on a nutrition label or grams per day, and it certainly isn’t all the same.
What if the real issue isn’t that we’re eating too little fibre, but that the fibre we’re eating isn’t what it used to be? To understand why and what that means, we must go back to where fibre begins, which is not in your gut, not on your plate, but in the soil.
From soil to plant: where fibre is built
Plants don’t grow in isolation. Their roots exist within a living underground network, a vast microbial ecosystem which interacts with fungi and other life in the soil and is known as the rhizosphere.
In this space, which can be thought of as similar to the microbiome in the digestive tract, billions of microbes interact continuously with plant roots. The plant releases carbon compounds and sugars into the soil. These are signals to the microbes to unlock nutrients such as nitrogen, phosphorus and trace minerals from organic matter that the plant cannot access alone. Microbes then enable the nutrients from the organic matter to be absorbed into the plant.
This relationship not only determines how well a plant grows. It determines how that plant is built, how many nutrients, minerals and polyphenols a plant has and the complexity of the fibres that will eventually feed your microbiome.
Research consistently shows that soil microbial diversity – the health of the biology in soil - drives nutrient cycling, enzyme activity and organic matter breakdown (Wang et al., 2017; Guo et al., 2025). In other words, the richer the microbial ecosystem within the soil, the more complex the biochemical environment surrounding the plant and this complexity really matters.
Fibre is not one thing; it’s a living architecture
When we talk about fibre, we are really describing a complex architecture of plant cell walls made up of cellulose, hemicellulose, pectins, resistant starches, lignin and polyphenol-bound fibres. These structures are built from carbon, but they are shaped by the conditions in which the plant grows.
Different environments produce different fibres. Different fibres feed different microbes. This is where soil biology becomes critical.
What happens when soil microbial diversity declines?
Over the past century, agricultural systems have shifted dramatically. Synthetic fertilisers have replaced biological nutrient cycling, monocultures have reduced ecological diversity, and soil disturbance has disrupted microbial networks. The result is a measurable decline in soil microbial biodiversity.
This causes subtle but important changes. Microbes are no longer able to break down complex organic matter as effectively. The biochemical richness of the soil declines, and plants begin to rely more on simpler, more readily available nutrients.
Studies show that diverse microbial communities are essential for breaking down complex plant materials like cellulose and lignin (Tom et al., 2022). Without this diversity, the system loses its ability to process complexity, and that loss ripples upward.
Simpler soils may produce simpler fibres
Plants grown in biologically active soils are exposed to a wide range of microbial signals and nutrients. This encourages the production of more complex biochemical structures, including diverse and functionally rich fibres. In contrast, plants grown in degraded soils often grow faster, contain more water and starch, and show reduced biochemical diversity.
While fibre content may appear similar on paper, the structure and complexity of that fibre can differ significantly. Research in food chemistry shows that plant cell wall composition varies widely, and that these differences directly influence how fibres behave biologically (López-Malvar et al., 2022). So, two carrots, two grains of wheat or two apples may both contain fibre, but not the same kind of fibre.
Why this matters for your gut microbiome
Your gut microbiome does not just need fibre. It needs diverse, complex fibre. These fibres are fermented by gut microbes in the lower intestine to produce short-chain fatty acids such as butyrate, which support gut lining integrity, immune function, inflammation regulation and even brain signalling.
However, not all fibres ferment in the same way. Research shows that more complex fibres, such as pectin-rich structures, produce very different microbial and metabolic responses compared to simpler fibre types.
If fibre complexity declines, the consequences are real for our health. Microbial diversity can be reduced, beneficial metabolite production can fall, and the gut ecosystem can become less resilient. This means someone can be eating “enough fibre” and still be microbially undernourished.
Most nutritional advice focuses on macronutrients, calories and fibre intake in grams. It rarely considers where that fibre came from, how it was grown, or what kind of microbial system produced it. This is the missing link. We are connected to the biology in our soils through the food that we eat. You can’t see this biology, but you can see the impacts when it is missing.
A new way to think about fibre
If we step back, a clearer picture begins to emerge. Healthy soil supports diverse microbes. These microbes drive complex nutrient exchange, which shapes richly structured plants. Those plants provide diverse fibre, which feeds a thriving gut microbiome.
The reverse is also true.
Degraded soil leads to reduced microbial diversity. This simplifies plant chemistry, reduces fibre complexity and ultimately limits the diversity of the gut microbiome. The result is various human health issues which are worsening and becoming chronic.
Where do we go from here?
We are only just beginning to understand how deeply intertwined these systems are. There are still gaps in the science, and researchers are actively exploring how soil biodiversity shapes plant chemistry and, ultimately, human health.
But the direction is clear. The future of nutrition will not simply be about eating more fibre or taking isolated supplements. It will be about restoring our connection to the earth, regenerating the biological complexity in which nutrient-rich foods are grown and reconnecting with the microbial world.
We believe that health does not start in the gut. It starts in the soil. The microbes that build life in the ground are the same ones that support life inside you.
When we lose microbial diversity in the soil, we do not just lose nutrients. We lose complexity, resilience and connection. Rebuilding that system is not about adding one thing back. It is about restoring the ecosystem.
References
Buchkowski, R.W., Benedek, K., Bálint, J., Molnár, A., Felföldi, T., Fazakas, C., Schmitz, O.J. and Balog, A. (2023) Plant chemical variation mediates soil bacterial community composition. Scientific Reports, 13, 6088. https://doi.org/10.1038/s41598-023-32935-4
Chauhan, A. et al. (2023) Role of soil microorganisms in plant health and nutrition. Sustainability. https://doi.org/10.3390/su151914643
Guo, W., Li, M.-H. and Qi, L. (2025) The contrasting roles of fungal and bacterial diversity and composition in shaping the multifunctionality of rhizosphere and bulk soils across large-scale bamboo forests. BMC Microbiology, 25, 252. https://doi.org/10.1186/s12866-025-03962-0
López-Malvar, A., Santiago, R., Souto, X.C. and Malvar, R.A. (2022) Cell wall composition impacts structural characteristics of the stems and thereby biomass yield. Journal of Agricultural and Food Chemistry, 70(10), pp.3136–3141. https://doi.org/10.1021/acs.jafc.2c04380
Tom, L.M., Aulitto, M., Wu, Y.-W., Deng, K., Gao, Y., Xiao, N., Rodriguez, B.G., Louime, C., Northen, T.R., Eudes, A., Mortimer, J.C., Adams, P.D., Scheller, H.V., Simmons, B.A., Ceja-Navarro, J.A. and Singer, S.W. (2022) Low-abundance populations distinguish microbiome performance in plant cell wall deconstruction. Microbiome, 10, 183. https://doi.org/10.1186/s40168-022-01377-x
Wang, R., Zhang, H., Sun, L., Qi, G., Chen, S. and Zhao, X. (2017) Microbial community composition is related to soil biological and chemical properties and bacterial wilt outbreak. Scientific Reports, 7, 343. https://doi.org/10.1038/s41598-017-00472-6
Mishra, S.K. and Bhatia, S. (2016) Emerging role of gut microbiota in health and disease. Journal of Translational Medicine, 14, 236. https://doi.org/10.1186/s12967-016-0975-7
