The human microbiome refers to the full range of microorganisms that live on and within human bodies. These microorganisms play a crucial role in the maintenance and development of the human body. The intestinal microbiome for instance is mainly composed of various microorganisms, which work in symbiosis, providing beneficial effects on the host individual: they produce vitamins, provide protection against pathogens and help regulate or adjust the functioning of the immune system.
Glyphosate works by disrupting a metabolic pathway (the shikimate pathway) in plants, which is essential for plant growth and development. Since mammals do not possess this specific pathway, glyphosate was considered to be non-toxic to humans and animals. However, the shikimate metabolic pathway is present in many microbes of the human microbiome.
Unfortunately, there is limited existing research on the effects of glyphosate exposure on the gut microbiome of humans. However, studies from in vitro and animal studies indicate that glyphosate exposure affects the gut microbiome. In mice, for instance, scientific findings indicate that exposure leads to morphological and functional changes in the gut microbiome, which are associated with behavioural changes that are similar to those observed in patients with neurodevelopmental disorders.
Existing studies show that over half of the bacteria in the human microbiome are intrinsically sensitive to glyphosate. Thus, glyphosate exposure to these sensitive bacteria may cause an imbalance in the diversity and abundance of microorganisms in the microbiome (known as dysbiosis). This may lead to an altered microbial community structure and function, and consequently, a potential emergence of disease.
Additionally, studies suggest that exposure to glyphosate may increase the resistance of pathogens to antimicrobial agents, such as antibiotics. Glyphosate stresses microorganisms, meaning that it disrupts their normal functioning by modifying the environment. Therefore, exposure to glyphosate may trigger a series of physiological changes in bacteria (known as a stress response). Because pathogens tend to have superior stress responses due to their greater adaptability under stressful conditions (Bote et al, 2019; Chowdhury et al, 1996), exposure to glyphosate may reduce the degree to which they are vulnerable to the effects of antibiotics. This can happen either as a response to stress or via mutations by changing the bacterial response to antibiotics.
US Right to know (2023), by Carey Gillam : Glyphosate: Cancer and other health concerns, microbiome disruption
US Right to know (2021), by Carey Gillam : New study finds glyphosate-related alterations in gut microbiome
The Guardian (2018) : Glyphosate shown to disrupt microbiome 'at safe levels', study claims
Forbes (2020) : Glyphosate Exposure Could Disrupt Human Gut Microbiome
Le Monde (2021): Le glyphosate peut perturber le microbiote à des doses très faibles, selon une étude internationale
Scientific research papers
Qixing Mao et al., “The Ramazzini Institute 13-week pilot study on glyphosate and Roundup administered at human-equivalent dose to Sprague Dawley rats: effects on the microbiome” (Environmental Health, 2018).
Rueda-Ruzafa, L. et al., “Gut microbiota and neurological effects of glyphosate”, (NeuroToxicology, 75, 2019).
Bote K, et al., “Minimum Inhibitory Concentration of Glyphosate and of a Glyphosate-Containing Herbicide Formulation for Escherichia coli Isolates - Differences Between Pathogenic and Non-pathogenic Isolates and Between Host Species”, (Front Microbiol. 2019).
Barnett JA, Gibson DL., “Separating the Empirical Wheat From the Pseudoscientific Chaff: A Critical Review of the Literature Surrounding Glyphosate, Dysbiosis and Wheat-Sensitivity”, (Front Microbiol. 2020).
Mesnage R et al., “Use of Shotgun Metagenomics and Metabolomics to Evaluate the Impact of Glyphosate or Roundup MON 52276 on the Gut Microbiota and Serum Metabolome of Sprague-Dawley Rats” (Environ Health Perspect. 2021).
Puigbò, P. et al., “Does Glyphosate Affect the Human Microbiota?” (Life 2022, 12).
Del Castilo I et al., “Lifelong Exposure to a Low-Dose of the Glyphosate-Based Herbicide RoundUp® Causes Intestinal Damage, Gut Dysbiosis, and Behavioral Changes in Mice”, (Int J Mol Sci. 2022).