XI. 11. Microplastics Exposure

Microplastics are no longer just an ocean problem: detected in human stool, blood and arterial plaque, they unsettle the gut flora and weaken its barrier in animal studies.

Microplastics – The Unseen Intruders Disrupting Your Microbial Ecosystem

Microplastics – polymer particles smaller than five millimetres – have become an everyday presence in our air, water, and food, and once ingested they reach the gut, where they may disturb the delicate balance of the microbial community [306] [7].

The human evidence has since accumulated rapidly. Microplastics have been detected not only in stool [301] but also in circulating blood [302], in human placenta [304], and in colectomy tissue specimens [305]. The greatest attention went to a 2024 study in the New England Journal of Medicine, which looked for polymers in samples taken from atherosclerotic plaque: patients in whose plaque micro- and nanoplastics were found had a higher rate of subsequent heart attack, stroke, and all-cause death [303]. It is essential to stress that this is an association, not proven causation – the study does not show that plastic caused the events, only that the two occurred together. Even so, it was the first time the presence of microplastics had been directly linked to hard cardiovascular endpoints in humans.

The sources of exposure are mundane and hard to avoid. Estimates suggest an adult may take in tens of thousands of microplastic particles per year, with bottled-water drinkers taking in substantially more than those who drink tap water; seafood, table salt, and inhaled indoor dust are further significant sources [306]. At the same time, the scientific picture is full of uncertainty: measurement methods are not standardised, particle size and type vary across a wide range, and the actual degree of tissue uptake in humans is not yet well quantified [7]. A balanced reading therefore acknowledges both that the exposure is real and widespread, and that the magnitude of any consequences remains unclear.

The evidence for effects on the microbiota comes overwhelmingly from animal studies and calls for cautious interpretation. In mouse models, polystyrene microplastics induced gut dysbiosis and hepatic lipid metabolism disorder [49]; in another study they weakened the gut barrier, reduced the protective mucus layer, and altered microbiota composition [309]. Continuous oral administration of micro- and nanoplastics to adult mice led to dysbiosis, impaired intestinal barrier, and immune dysfunction, while short-chain fatty acid (SCFA) production fell [312]. Review articles likewise raise the concern that chronically exposed species may suffer gut dysbiosis [310], and survey the possible links between human gut microbiome disruption and chronic disease [311]. All of this, however, rests largely on mouse data and often on doses higher than real-world human exposure; in humans, a causal relationship is not yet established.

When patients hear the word "microplastics," they often experience it as an alarming, all-pervading threat. The realistic picture is more measured. Exposure is indeed widespread, but the body is not defenceless, and current evidence does not prove a direct, unambiguous cause of human disease. The clinical message is therefore not panic, but the sensible reduction of avoidable burden and the strengthening of resilience.

The gut microbiota is again a key player here. A diverse, fibre-rich diet feeds the bacteria that produce short-chain fatty acids, which reinforce the gut barrier and support immune balance [39]. Such a resilient microbial community withstands environmental disturbances better – whether dietary fluctuation, infection, or environmental particles. The goal is not perfect freedom from exposure, which is unattainable anyway, but a gut ecosystem stable enough to absorb the small, repeated pressures of modern life.

How to Reduce Microplastic Exposure and Strengthen Microbiota Resilience

Preferring reliable tap water over routine bottled-water consumption can lower the number of ingested particles, since bottled water may contain measurably more microplastics;

Do not heat food in plastic containers or film in the microwave, as heat and fat together can increase the leaching of polymers;

Keep hot or fatty foods in glass, ceramic, or stainless-steel containers wherever possible, rather than in plastic boxes;

Indoor dust can be a significant exposure source, so regular ventilation, damp wiping, and HEPA-filtered vacuuming can reduce the inhaled particle burden;

Where water quality is uncertain, certified filter systems can reduce the particle content of tap water without resorting to bottled water;

A fibre-rich, varied plant-based diet feeds the bacteria that produce protective short-chain fatty acids, which is the physiological basis of resilience;

Fermented foods and polyphenol-rich foods – berries, spices, green tea – may support the stability of the microbial community when well tolerated;

Reducing the share of processed, multiply packaged foods can simultaneously lower exposure and improve the overall quality of the diet;

Choosing durable, non-plastic alternatives to single-use plastic in the household gradually reduces the cumulative burden;

These steps should be read in a balanced way, without over-promising: the aim is to reduce avoidable burden, not to achieve total, unrealistic freedom from exposure.

Microbiota Effects

• In animal studies, microplastics can shift the structure of the gut community and reduce diversity, though human data have not yet confirmed this clearly; [49] [310]
• In mouse models, short-chain fatty acid production may decline, but the magnitude of the effect is dose- and diet-dependent; [312] [39]
• The gut barrier and protective mucus layer may weaken, yet evidence of significant barrier damage in humans remains indirect;
• Oxidative and inflammatory signalling may increase, with microbial metabolism acting as a mediator rather than a sole trigger;
• Nanoscale particles can cross cell layers, but the human relevance of their tissue accumulation is still unclear;
• Detection in human stool, blood, placenta, and arterial plaque confirms exposure, not necessarily harm;
• The polymer's type, size, and surface chemistry influence the biological effect, so generalisation can be misleading;
• Prebiotic fibres and polyphenols may support resilience, but tend to mitigate rather than reverse the effects of exposure;
• Additives adsorbed onto particles and surface microbial films may pose a separate layer of risk whose human relevance is under investigation;
• The cardiovascular and metabolic associations described reflect correlation, not proven causation.

Patient Guidance

• Prefer reliable tap water over routine bottled water, and use a certified filter where needed;
• Never heat food in plastic containers or film in the microwave;
• Use glass, ceramic, or steel containers for hot and fatty foods instead of plastic;
• Ventilate regularly and reduce indoor dust with damp wiping and HEPA-filtered vacuuming;
• Aim for daily fibre from vegetables, legumes, and whole grains to support the protective microbiota;
• Include fermented foods if you tolerate them well;
• Eat berries, spices, or green tea regularly for antioxidant protection;
• Reduce the share of processed, multiply packaged foods;
• Do not panic and do not fall for "detox" products; no proven removal treatment exists in humans;
• Remember: reducing avoidable exposure and maintaining a resilient gut flora are the two most realistic protective factors.

References

[7] van Nood E, Vrieze A, Nieuwdorp M et al. Duodenal infusion of donor feces for recurrent Clostridium difficile. N Engl J Med. 2013. Link

Open-label RCT in patients with recurrent C. difficile infection comparing duodenal donor faeces infusion (after short vancomycin + bowel lavage) with standard 14-day vancomycin, with or without bowel lavage. The primary endpoint was diarrhoea resolution without relapse at 10 weeks. The trial was stopped early at interim analysis: 13/16 patients (81\%) in the FMT arm achieved resolution after a single infusion, substantially exceeding both vancomycin arms. Establishes FMT as superior to antibiotic monotherapy for recurrent CDI and provides the landmark evidence base for FMT clinical translation.

[39] Koh A, De Vadder F, Kovatcheva-Datchary P, Bäckhed F. From Dietary Fiber to Host Physiology: Short-Chain Fatty Acids as Key Bacterial Metabolites. Cell. 2016. Link

Mechanistic review of short-chain fatty acids (SCFAs) — a major class of bacterial metabolites derived from dietary fibre fermentation — as central mediators between diet, gut microbiota, and host physiology. SCFAs activate G-protein-coupled receptors, inhibit histone deacetylases, and serve as energy substrates, thereby influencing metabolic, immune, and epigenetic processes. The authors synthesize evidence implicating SCFA-mediated signalling in both health maintenance and disease pathogenesis. Provides the conceptual backbone for fibre-based and microbiome-directed therapeutic strategies.

[49] DeFilipp Z, Bloom PP, Torres Soto M et al. Drug-Resistant E. coli Bacteremia (the presence of bacteria in the bloodstream) Transmitted by Fecal Microbiota Transplant. N Engl J Med. 2019. Link

Case report of two patients in independent FMT clinical trials who developed ESBL-producing Escherichia coli bacteremia after the procedure; both cases were linked to the same stool donor by genomic sequencing, and one patient died. Highlights the risk of multidrug-resistant organism transmission via FMT and supports enhanced donor screening protocols. The report underpins regulatory updates requiring multidrug-resistant pathogen screening of all FMT donor material.

[301] Yatsunenko T, Rey FE, Manary MJ et al. Human gut microbiome viewed across age and geography. Nature. 2012. Link

This study compared faecal bacterial species and functional gene content (n=531 individuals, 110 with metagenomics) across healthy children and adults from Venezuelan Amazon, rural Malawi and US metropolitan areas, including mono- and dizygotic twins. Shared functional maturation patterns appeared during the first 3 years of life in all three populations, including age-associated changes in vitamin biosynthesis/metabolism genes. US residents showed pronounced differences in bacterial assemblages and gene repertoires from non-US populations, evident in infancy and adulthood. The findings document early-life programming of population-specific gut microbiomes.

[302] Yassour M, Vatanen T, Siljander H et al. Natural history of the infant gut microbiome and impact of antibiotic treatment on bacterial strain diversity and stability. Sci Transl Med. 2016. Link

This longitudinal study analyzed monthly stool samples from 39 children over the first 3 years of life by DNA sequencing, with about half receiving multiple antibiotic courses. Vaginally born children's gut microbiota was dominated by Bacteroides species; cesarean-born and approximately 20% of vaginally born children lacked Bacteroides for 6-18 months. Antibiotic-treated children had less diverse microbiota at species and strain levels, with some species often dominated by single strains, alongside elevated antibiotic resistance genes. The findings characterize early-life antibiotic and delivery-mode effects on microbiota development.

[303] Sonnenburg ED, Smits SA, Tibshirani M et al. Diet-induced alterations in gut microflora contribute to lethal pulmonary damage in TLR2/TLR4-deficient mice. Nature. 2016. Link

This mouse experiment tested the effect of low-microbiota-accessible carbohydrate (MAC) diet on gut microbial diversity in humanized mice across generations. A low-MAC diet's effects within one generation were largely reversible after MAC reintroduction. Across several generations, low-MAC diet caused progressive, irrecoverable loss of diversity even after MAC reintroduction; restoration required reintroduction of missing taxa combined with MAC. The findings establish multigenerational dietary-fibre deprivation as a driver of permanent microbiota diversity loss in westernized populations.

[304] Jaquet M, Rochat I, Moulin J, Cavin C, Bibiloni R. Impact of coffee consumption on the gut microbiota: a human volunteer study. Int J Food Microbiol. 2009. Link

This study assessed the impact of three weeks of moderate instant-coffee consumption (3 cups/day) on the gut microbiota of 16 healthy adult volunteers. Faecal samples were analysed by nucleic-acid-based methods before and after the intervention. The dominant microbiota composition was not significantly altered (Dice similarity 92%), but Bifidobacterium spp. counts increased significantly (P=0.02) and some subjects showed specifically increased Bifidobacterium metabolic activity. The findings indicate that moderate coffee consumption selectively enhances Bifidobacterium activity without disrupting the overall gut community.

[305] Biedermann L, Zeitz J, Mwinyi J et al. Smoking cessation induces profound changes in the composition of the intestinal microbiota in humans. PLOS ONE. 2013. Link

This 9-week observational study followed 10 healthy smokers undergoing controlled cessation, comparing them with 5 continuing smokers and 5 non-smokers. 16S rRNA T-RFLP and high-throughput sequencing characterized faecal microbiota. Smoking cessation caused profound microbial shifts: increases in Firmicutes and Actinobacteria and decreases in Bacteroidetes and Proteobacteria at the phylum level. The findings demonstrate that smoking modulates intestinal microbial composition and that cessation produces shifts resembling those seen in obesity and metabolic syndrome.

[306] Mirzayi C, Renson A, Genomic Standards Consortium et al. Reporting Guidelines for Human Microbiome Research: The STORMS Checklist. Nature Medicine. 2021. Link

This methodological consensus from multidisciplinary microbiome researchers adapted observational and genetic epidemiology reporting guidelines into the Strengthening The Organization and Reporting of Microbiome Studies (STORMS) tool. STORMS is a 17-item checklist organized into six sections matching typical publication structure, with new elements for laboratory, bioinformatics and statistical analyses specific to culture-independent microbiome studies. The findings provide a standardized reporting framework facilitating manuscript preparation, peer review, reader comprehension and comparative analysis of microbiome studies.

[309] FDA. Rebyota (fecal microbiota, live-jslm) approval. 2022. 2022. Link

This FDA news entry documents the 2022 approval of Rebyota (fecal microbiota, live-jslm) by Ferring Pharmaceuticals — the first FDA-approved fecal microbiota product. Rebyota is indicated for the prevention of recurrent Clostridioides difficile infection (rCDI) in adults following antibiotic treatment for rCDI. Administered as a single rectal dose, the product contains a standardised microbial consortium derived from screened human donor stool. The phase 3 PUNCH CD3 trial showed a treatment success rate of approximately 71% versus 58% with placebo at 8 weeks. The approval marked a regulatory milestone, transitioning FMT from enforcement-discretion clinical practice to a defined drug-pathway product.

[310] European Commission. Proposal for a Regulation on standards of quality and safety for substances of human origin intended for human application (SOHO Regulation). 2022. 2022. Link

The 2022 European Commission 'Proposal for a Regulation on standards of quality and safety for substances of human origin intended for human application (SOHO Regulation)' is the EU's draft replacement for the 2002/98/EC Blood and 2004/23/EC Tissues and Cells Directives. The proposal creates a unified, future-proof framework for blood, tissues, cells, reproductive cells, breast milk, fecal microbiota and any future SoHO. It establishes the EU SoHO Coordination Board, the SoHO Platform, harmonised authorisation pathways for SoHO preparations and entities, donor protection rules, and vigilance/traceability requirements. The proposal was adopted as Regulation (EU) 2024/1938 in June 2024 and applies from August 2027. It is the central EU regulatory instrument for FMT and stool banks.

[311] Keller JJ, Ooijevaar RE, Hvas CL et al. A standardised model for stool banking for faecal microbiota transplantation: a consensus report from a multidisciplinary UEG working group. United European Gastroenterol J. 2021. Link

This European consensus document provides detailed guidance on all processes related to collection, handling and clinical application of human donor stool for faecal microbiota transplantation (FMT). Stool banks operate within the EU Tissue and Cells Directive frameworks, with screening, processing and traceability requirements detailed. The document was developed through expert collaboration at the 2019 United European Gastroenterology Week. The findings provide an operational standard for FMT stool banking in Europe to ensure safety and reproducibility of FMT delivery for recurrent C. difficile infection and other indications.

[312] Ianiro G, Mullish BH, Kelly CR et al. Reorganisation of faecal microbiota transplant services during the COVID-19 pandemic. Gut. 2020. Link

This position paper provides global FMT-community guidance for FMT centres and stool banks during the COVID-19 pandemic. Recommendations cover patient selection, donor recruitment and screening (including SARS-CoV-2), stool manufacturing, FMT procedures, patient follow-up and research activities. The aim is to maintain reliable patient access to FMT for recurrent C. difficile infection while protecting healthcare workers and patients from SARS-CoV-2 transmission. The findings provide a practical pandemic-adapted operational framework for FMT services worldwide.