Herbicides & Health

Herbicides are chemicals designed to kill unwanted plants (weeds). Unlike insecticides and fungicides, which are often applied directly to fruits and vegetables, herbicides are commonly used at the field level, especially in large-scale grain, legume and oilseed production.

The most widely used herbicide globally is glyphosate, but many others are also used depending on crop, region and farming system.

This page focuses on what people with gut, immune or inflammatory conditions should know.

1) Where herbicide exposure mainly comes from

For most people, dietary exposure to herbicides comes primarily from staple crops, not fruit:

• Wheat and other cereals

• Oats and barley

• Rice

• Corn and soy

• Legumes

• Some vegetable oils

A key difference from insecticides is timing. Certain herbicides are applied:

• Early (weed suppression), or

• Late in the growing cycle (e.g., pre-harvest crop desiccation in some systems)

Late application increases the likelihood that residues remain on harvested grain, even after processing.

Bottom line:
Herbicide exposure is more strongly linked to how much of a food you eat (staple volume) than to surface spraying of individual fruits or vegetables.

2) Gut microbiome effects

Glyphosate works by inhibiting the shikimate pathway, a metabolic pathway absent in human cells but present in many gut bacteria.

Experimental and review evidence suggests that herbicide exposure can:

• Alter gut microbial composition (dysbiosis)

• Reduce production of beneficial microbial metabolites (e.g., short-chain fatty acids)

• Shift microbial balance toward more inflammatory profiles

These effects have been observed at doses near or below regulatory thresholds in animal and in-vitro models.

Bottom line:
While human data are still emerging, there is credible mechanistic evidence that some herbicides can perturb gut microbial ecosystems, which is relevant for people managing gut or immune-mediated conditions.

3) Intestinal permeability (“leaky gut”)

Several herbicides have been shown in cell and animal studies to:

• Disrupt tight-junction proteins

• Increase intestinal permeability

• Alter mucosal barrier function

Increased permeability allows microbial products (e.g., endotoxin) to enter circulation more readily, activating immune and inflammatory pathways.

Bottom line:
Direct human evidence is limited, but biological plausibility is strong, and findings are consistent with pathways implicated in chronic inflammation and autoimmunity.

4) Inflammation, autoimmunity & arthritis relevance

Most large epidemiological data come from occupational exposure, not diet. These studies show:

• Increased risk of inflammatory and autoimmune outcomes with long-term herbicide exposure in agricultural settings

• Variable results depending on compound, exposure intensity and duration

Dietary exposures are far lower than occupational levels, but chronic low-dose exposure over decades remains an area of active research.

Bottom line:
Associations do not prove causation, but for people with inflammatory disease, a precautionary, exposure-minimising approach is reasonable.

5) Cancer and broader health considerations

Glyphosate is classified by the International Agency for Research on Cancer (IARC) as:

• Group 2A: “Probably carcinogenic to humans” (hazard classification)

Regulatory agencies such as EFSA and EPA conclude that:

• Glyphosate is unlikely to pose a cancer risk to consumers under approved uses, though uncertainties and data gaps remain.

Bottom line:
Risk assessment depends on dose, duration, formulation and exposure context. Hazard classification and regulatory risk conclusions answer different questions and are not mutually exclusive.

6) Practical ways to reduce herbicide exposure

You don’t need to eliminate grains or legumes to lower exposure.

Smart strategies include:

• Prioritise organic or certified low-residue grains (especially oats, wheat products and rice) if budget allows

• Rotate grain choices rather than relying heavily on one staple

• Rinse legumes and grains before cooking

• Choose minimally processed whole foods over refined products when possible

• Maintain a diverse, fibre-rich diet to support microbial resilience

Bottom line:
The health benefits of whole grains are substantial. The goal is smarter sourcing, not avoidance.

References

1. International Agency for Research on Cancer (IARC). IARC Monograph 112: Glyphosate. Lyon, 2015.
2. EFSA. Peer review of the pesticide risk assessment of the active substance glyphosate. EFSA Journal 2023;21(10):8164.
3. Mesnage R, Antoniou MN. Low-dose glyphosate exposure alters gut microbiota composition and intestinal function. Chemico-Biological Interactions, 2023.
4. Silva V et al. Effects of glyphosate exposure on intestinal microbiota and gut structure: a systematic review. Food & Function, 2024.
5. Gama J, Neves B, Pereira A. Chronic effects of dietary pesticide and herbicide exposure on the gut microbiome and neuro-immune pathways. Frontiers in Microbiology 2022;13:931440.
6. Mao Q et al. Glyphosate-based herbicides and intestinal barrier integrity: mechanistic evidence from experimental models. Environmental Research, 2023.
7. U.S. FDA. Pesticide Residue Monitoring Program Annual Report. Most recent edition.
8. European Food Safety Authority (EFSA). Annual Report on Pesticide Residues in Food.