Glyphosate (Roundup) shapes the gut microbiome: Latest evidence

The link between popular herbicide glyphosate and the gut microbiome has been revealed in a brand new study published in October 2023 in the journal Gut Microbes.

Glyphosate, a widely used herbicide, has increasingly found its way into our environment, leading to its unwitting consumption by humans through contaminated crops, drinking water, and polluted air.

Glyphosate in Our Bodies:

Recent studies have revealed that glyphosate is alarmingly present in the bodies of both farmers and the general public. In South Carolina, 90% of farmers had glyphosate in their urine at concentrations of up to 233 parts per billion (ppb). In the USA, 60-95% of the general public had glyphosate in their urine at concentrations of 2-3 micrograms per litre (μg/L), while in Europe, this ranged from 40-50% with concentrations of less than 1 μg/L. Even more concerning, 30% of examined neonates had glyphosate in their urine at concentrations of less than 1.06 μg/L. This exposure could result from the consumption of breast milk, baby formula, or the ability for glyphosate to cross the placenta barrier.

Glyphosate’s Widespread Use:

Glyphosate has been in use since 1974, and with the introduction of Roundup™-ready resistant crops in 1996, its presence in the environment has surged. Humans and livestock are ingesting glyphosate through drinking water, crops, and contaminated air, potentially causing a myriad of health issues. It’s important to note that while there’s a correlation between glyphosate exposure and various disorders, there’s no conclusive evidence establishing causation.

Mixed Research Findings:

Research on glyphosate’s impact on human health is somewhat contradictory. Some studies suggest a link between glyphosate and cancer development, increased asthma severity, and arthritis, while others claim no such connection. Notably, all human studies rely on self-reporting of glyphosate exposure through questionnaires, making the data somewhat limited. In contrast, animal studies have shown that glyphosate can harm critical bodily systems, even at levels below the acceptable daily intake (ADI) established by the European Food Safety Authority (EFSA).

Glyphosate and the Gut Microbiome:

Glyphosate exposure can alter the gut microbiome, causing an increase in certain bacteria and a decrease in others. These changes are associated with various health effects, including reproductive toxicity, neurodevelopmental disturbances, and more. However, these studies used glyphosate concentrations above the ADI. A study that used the EFSA-determined ADI reported no significant disturbances to the gut microbiome.

Glyphosate’s impact on gut bacteria is not uniform, and certain bacterial groups show varying degrees of resistance. Here are some key findings:

Resistance Patterns:

  • Bacillota are generally more resistant to glyphosate compared to Actinomycetota and Pseudomonadota.
  • Pathogenic bacteria like Escherichia coli, Salmonella enterica, and Salmonella enterica serotype Typhimurium showed higher resistance to glyphosate compared to host-associated commensal bacteria.

Minimum Inhibitory Concentrations (MICs):

  • One study examined the minimum inhibitory concentrations (MICs) of glyphosate for pathogenic and commensal bacteria. Pathogenic strains had a significantly higher MIC (20-80 mg/mL) than commensal strains (5-10 mg/mL). This suggests that glyphosate ingestion could potentially select for pathogenic bacteria in the gut microbiome.

Glyphosate Sensitivity/Resistance:

  • A study analyzing 101 bacterial species found that 54% of gut bacteria were sensitive to glyphosate. Examples include Faecalibacterium and Bifidobacterium which are crucial for good health. 
  • About 29% of bacterial species were potentially resistant, including Clostridium, Ruminococcus, and Dorea. An increase in these resistant microbes is associated with diseases like Inflammatory Bowel Disease (IBD).

Potential Sensitivity:

  • Another study examined 890 bacterial strains from 101 species in the gut microbiome. It predicted that 12-26% of these bacteria are potentially sensitive to glyphosate.
  • Some bacteria have evolved to produce enzymes that break down glyphosate and use its degradation products, such as phosphate, as a nutrient. An example is certain strains of Pseudomonas.

The Impact on Gut Health:

Glyphosate’s effects on gut bacteria are complex and multifaceted. While some bacteria can resist glyphosate’s influence, others may be sensitive, potentially leading to imbalances in the gut microbiome. The changes in gut bacteria composition and function have been associated with conditions like Inflammatory Bowel Disease (IBD), highlighting the importance of understanding the consequences of glyphosate exposure on gut health.

It’s essential to conduct further research, both in animal models and controlled human studies, to unravel the full extent of glyphosate’s impact on gut bacteria and its potential implications for human health. As the European Food Safety Authority (EFSA) plans to discontinue the use of glyphosate in the EU after December 2023, it becomes even more crucial to gain a comprehensive understanding of the effects of this herbicide on the gut microbiome and overall health.

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