05
Sep
Reinforcing Scientific Findings, Insecticide Permethrin Found To Alter Gut Microbiome, Causing Obesity
(Beyond Pesticides, September 5, 2025) A study in Journal of Agricultural and Food Chemistry finds permethrin, a commonly used synthetic pyrethroid insecticide, to be disruptive to the gut microbiome, altering microbiota and leading to increased formation of fat cells (adipogenesis) and metabolic disorders. With an aim to “comprehensively elucidate the effects of permethrin on gut microbiota, lipogenesis, and the associated molecular mechanisms,†the study explores the adverse effects of permethrin exposure in adult mice through multiple experiments.
“Our study provides the first in vivo [in a living organism] evidence suggesting a potentially causal relationship between permethrin exposure and the development of obesity, potentially mediated by specific gut microbiota-derived metabolites,†the researchers explain. They continue, “Notably, this work is the first to define a distinct microbiota−metabolite−host axis as a critical mediator of environmental toxicant-induced metabolic dysfunction.â€
Permethrin is widely used as an insecticide on crops, such as cotton, corn, and wheat, as well as on livestock, in indoor and outdoor areas, and for treating lice and scabies. Mosquito abatement programs often utilize permethrin, further adding to the various exposure routes of this neurotoxic chemical. (See additional uses and health effects of permethrin in Beyond Pesticides’ Gateway on Pesticide Hazards and Safe Pest Management here.)
Since pyrethroids are lipophilic compounds (“fat loving†or having an affinity for fats, oils, and other non-polar substances), they are able to extensively distribute throughout the body and can encompass many vital organs including the liver, adipose tissue, intestines, nervous system, stomach, and kidneys.
Previous research by the study authors demonstrates that permethrin promotes weight gain and exacerbates comorbidities associated with obesity. (See here and here.) Obesity is a chronic metabolic disorder linked to type 2 diabetes, fatty liver, and cardiovascular diseases, and is influenced by the gut microbiome. Any imbalance of gut microbiota can lead to a multitude of adverse health impacts including obesity.
Study Methodology and Results
To determine the effects of permethrin exposure in adult mice, the current study performed multiple experiments that included an insulin and glucose tolerance test, plasma and liver lipid measurements, evaluation of the gut barrier integrity, and intestinal microbial sequencing and analysis.
“To study the effects of permethrin on the development of obesity in the mice model, the permethrin-treated group (Per) was administered permethrin orally to C57BL/6J mice for 12 weeks, while the control group (Con) was maintained on a high-fat diet,†the authors share. As a result, permethrin “significantly raised body weight, epididymal white adipose tissue (eWAT), and liver index without impacting food consumption.†The exposed group also shows a pronounced rise in blood glucose and altered serum levels.
Permethrin exposure induces substantial alterations in the composition of gut microbiota. Not only did exposed mice have greater permeability of the gut epithelial barrier, but “analysis of gut microbiota revealed that following permethrin treatment, there was a notable decrease in the ACE index [a statistical measurement of diversity in the gut microbiome].†Changes in microbiota at the phylum level reveal a marked increase in the proportion of Firmicutes and a significant decrease in the proportion of Bacteroidetes. These changes caused a 151% elevation in the Firmicutes/Bacteroidetes (F/B) ratio.
“At the genus level, we observed a notable decrease in the proportion of Intestinimonas, Anaerovorax, Faecalibacterium, Ruminiclostridium, Peptococcus, Bacteroides and UBA1819 within the Per group,†the researchers report. They continue, “Conversely, a notable increase was observed in the proportion of Prevotella_1, Eubacterium_brachy_group, Eubacterium_nodatum_group, Prevotella_7, Ruminococcaceae_UCG-013, Family_XIII_AD3011_group, Family_XIII_UCG-001, and Marvin- bryantia within the Per group.â€
These results highlight how permethrin significantly influenced the delicate balance of gut microbiota and can lead to additional health implications and diseases. A follow-up experiment involving fecal microbiota transplantation (FMT) further shows the causal role of microbiota in fat accumulation and impacts from permethrin exposure.
The “FMT from permethrin-treated donors induced an imbalance of gut microbiota in mice,†the authors write. In particular, the treatment group shows a 27% increase in Firmicutes abundance, as well as increased lipid accumulation. “[T]ransplanting the intestinal microbiota in sterile mice revealed that microbiota derived from the Per group substantially aggravated the development of obesity and insulin resistance in the subjects via FMT experiments,†the researchers note.
Additional analysis shows permethrin alters the fecal composition of bile acid derivatives, diacylglycerophosphoglycerols, fatty acids, and indoles and their derivatives. The observed lower indole levels could foster obesity and fatty liver progression by regulating lipid oxidation genes. The gut microbial dysbiosis can lead to enhanced intestinal permeability, allowing microbial metabolites to enter the liver and further influence hepatic lipids and promote obesity. (See studies here and here.)
“Hence, permethrin potentially modulated the composition of gut microbiota, thereby affecting the production of SCFAs [short-chain fatty acids] and indole and subsequently initiating lipogenesis, ultimately resulting in obesity, which might provide new insight into the mechanism of permethrin,†the authors conclude.
This study highlights the significant impact of permethrin on the liver and adipose tissue, while mirroring natural exposure patterns and concentrations. “Our study emphasizes the significant impact of permethrin, a common pesticide, on obesity, insulin resistance, and gut microbiota composition in mice,†the researchers summarize. They continue: “We found that permethrin dramatically alters gut microbiota, particularly Firmicute and Bacteroidetes, reducing the production of microbial metabolites (butyrate and indole), which is crucial for preventing obesity… In summary, our current results revealed a causal relationship between the development of obesity and gut microbiota.â€
Previous Research
Additional research cited in the current study highlights the molecular mechanisms underlying lipid accumulation that can be affected following pesticide exposure. Particularly, studies show the effects in adipocytes induced by deltamethrin, another pyrethroid insecticide, focusing on cellular-level processes. (See here and here.) Another study of Xenopus laevis exposed to cis-bifenthrin shows “a disturbance within the delicate balance of the gut microbiota and nonalcoholic fatty liver disease.â€Â
Research involving permethrin shows “shifts in gene expression and deoxyribonucleic acid (DNA) methylation, with the potential to disrupt glutamatergic signaling across generations, thus influencing behavioral patterns,†as well as increases to fatty acid synthesis and adipogenesis. Prolonged exposure to permethrin also provokes liver and kidney damage. (See studies here, here, here, here, and here.)
Previous Daily News coverage connects permethrin with rheumatoid arthritis, adverse effects on women’s reproductive health, impaired memory and learning, thyroid dysfunction, and mortality in birds and butterflies, among others. (See the Daily News archive for permethrin here for additional articles.)
In particular, two studies within the past year also link permethrin, and other pesticides, to impacts on the gut microbiome and higher risks for obesity. See Study Maps the Gut Microbiome and Adverse Impacts of Pesticide Residues and Study Links Numerous Chemical Families of Pesticides to Endocrine Disrupting Effects, Including Obesity for more information.
Organic Solution
To mitigate these health risks, the adoption of organic land management as a holistic solution is imperative. The only way to truly protect health and the environment is to remove the use of petrochemical pesticides and synthetic fertilizers, especially in agriculture that contaminates food, water, and air.
Organic land management is proven to be a sustainable and profitable alternative to toxic chemical use with higher crop yield, with additional benefits of protecting and enhancing biodiversity, increasing soil health, providing health benefits to those who adopt an organic diet, and mitigating climate change, among others.
To add your voice to the organic movement, take action to tell Congress to stand up for health and the environment. Make The Safer Choice to avoid hazardous home, garden, community, and food use pesticides and join the Parks for a Sustainable Future program. You can also sign up to get Action of the Week and Weekly News Update emails sent directly to your inbox and learn more about the health and environmental benefits of organic here and here.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Lin, J. et al. (2025) Permethrin Stimulates Fat Accumulation via Regulating Gut Microbiota and Its Metabolites in Mice, Journal of Agricultural and Food Chemistry. Available at: https://pubs.acs.org/doi/10.1021/acs.jafc.5c05013.
