Glyphosate is an organophosphorus compound and one of the most widely used broad-spectrum herbicides. Its primary use is in agriculture to control weeds in fields of genetically modified crops that are resistant to its effects, and in non-agricultural settings like gardening and forestry. The gut microbiome is the community of microorganisms, including bacteria, fungi, and viruses, residing in the digestive tract. This ecosystem is involved in various physiological processes, from digestion and nutrient absorption to immune system development. The widespread use of glyphosate has raised questions about its impact on this microbial balance.
Glyphosate’s Mechanism and Human Exposure
Glyphosate’s effectiveness as an herbicide stems from its ability to disrupt a metabolic process in plants and some microorganisms. It works by inhibiting an enzyme called 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). This enzyme is part of the shikimate pathway, a metabolic route used to produce aromatic amino acids like phenylalanine, tryptophan, and tyrosine. By blocking this pathway, glyphosate prevents the synthesis of these amino acids, leading to the plant’s death.
Human exposure to glyphosate occurs mainly through the consumption of food and water that contain residues of the herbicide. Because of its widespread use, glyphosate residues can be found in a variety of food products, particularly crops where the herbicide is used to dry them down before harvest. These can include:
- Non-organic oats
- Wheat
- Soy
- Lentils
While ingestion is the main route of exposure for the general population, individuals who work directly with glyphosate, such as agricultural workers, may experience higher levels of exposure through skin contact and inhalation. The presence of glyphosate and its primary metabolite, aminomethylphosphonic acid (AMPA), has been detected in human blood and urine samples, which confirms that the compound is absorbed by the body. However, it is excreted within a few days.
The Shikimate Pathway in Gut Bacteria
Glyphosate was long considered to have low toxicity in humans because human and other animal cells do not possess the shikimate pathway. Animals instead obtain essential aromatic amino acids through their diet. A significant portion of the bacteria residing in the human gut, however, do utilize the shikimate pathway to synthesize these same amino acids for their own survival and growth. This distinction forms the basis for concern regarding glyphosate’s effects on the gut microbiome.
Because many beneficial gut bacteria rely on the shikimate pathway, they are vulnerable to glyphosate’s inhibitory action. Research suggests that an estimated 54% of human gut bacterial species are potentially sensitive to glyphosate. This includes beneficial genera such as Lactobacillus and Bifidobacterium.
The inhibition of the EPSPS enzyme in these susceptible bacteria can hinder their ability to produce the aromatic amino acids needed for their proliferation. In contrast, some pathogenic bacteria have developed resistance to glyphosate and are not affected by its mechanism. This disparity in sensitivity could lead to an imbalance in the gut’s microbial composition.
Research on Microbiome Alterations
Scientific investigations into how glyphosate affects the gut microbiome have used various models, including in vitro (laboratory-based) and animal studies. These studies provide evidence that glyphosate exposure can alter the composition and function of the gut’s microbial community. The research indicates that glyphosate can suppress the growth of beneficial bacteria while allowing more resistant, and potentially pathogenic, bacteria to flourish.
Animal studies, particularly in rats and bees, have demonstrated shifts in the gut microbiome following glyphosate exposure. For instance, some studies on rats reported a decrease in the abundance of beneficial bacteria like Lactobacillus and Bifidobacterium species, while observing an increase in populations of bacteria such as Clostridium and Salmonella. Research on bees has also shown that glyphosate exposure can disrupt their gut microbiome, making them more susceptible to infections.
Much of this research has been conducted on animals, and the findings may not directly translate to humans. Studies involving human subjects are more limited and often rely on self-reported exposure levels. Furthermore, some studies use glyphosate concentrations that are higher than the acceptable daily intake (ADI) levels, making it difficult to draw firm conclusions about the effects of typical dietary exposure.
Potential Health Implications of Dysbiosis
The disruption of the gut microbiome, a condition known as dysbiosis, can have a range of health consequences. A healthy gut microbiome is involved in many bodily functions, including the digestion of nutrients, the synthesis of certain vitamins, and the regulation of the immune system. It also provides a protective barrier against invading pathogens.
When the balance of the gut microbiome is disturbed, these functions can be impaired. An overgrowth of pathogenic bacteria and a reduction in beneficial microbes can lead to a state of chronic inflammation in the gut. This has been linked to a variety of gastrointestinal issues and may affect the integrity of the intestinal lining, a condition sometimes referred to as increased intestinal permeability.
An imbalanced gut microbiome has been associated with health issues beyond the digestive system. Alterations in the gut-brain axis, the communication network between the gut and the brain, have been linked to changes in mood and behavior. While research continues to evolve, the potential for glyphosate to contribute to dysbiosis highlights the connection between environmental exposures, the gut microbiome, and overall human health.