Does Roundup® Residue on Food Impact your Microbiome?

The herbicide glyphosate (Roundup® and other tradenames) works by inhibiting synthesis of aromatic amino acids in the shikimate pathway, which is active in plants as well as bacteria, but not in mammalian species. Thus while glyphosate cannot adversely affect humans via its primary mode of action, the possibility that it could affect the bacteria of the human microbiome exists. Researchers from the Technical University of Denmark and Aarhus University investigated this question using an in vivo trial in rats.

In initial in vitro experiments, the researchers found that the minimum inhibitory concentration of a commercial glyphosate formulation for bacteria representative of the human gut microbiota was much lower in media which was not supplemented with aromatic amino acids compared to media with supplementation of those amino acids.

Does Roundup® Residue on Food Impact your Microbiome?
Graphical abstract from Nielsen, et al., 2018.

Sprague Dawley® rats from Taconic Biosciences were exposed to glyphosate on a daily basis for two weeks via oral gavage. Only very limited differences in the gut microbiome of rats were observed between control and glyphosate treatment groups. The researchers attributed this minimal microbiome perturbation to the presence of sufficient levels of aromatic amino acids in the gut, which can substitute for amino acids which would normally be synthesized by the bacteria.

While this work is not definitive and may not translate to humans who are malnourished or on special diets, it does provide some evidence that glyphosate exposure has limited impact on the human microbiome.

Nielsen, L. N. C. B.; Roager, H. M.; Casas, M. E.; Frandsen, H. L.; Gosewinkel, U.; Bester, K.; Licht, T. R.; Hendriksen, N. B.; Bahl, M. I. Environmental Pollution 2018, 233, 364-376.