Microplastics, Gut Microbiota, and Obesity: An Emerging Environmental Health Concern

Microplastics (MPs) are now regularly found in human feces, tissues, drinking water, and indoor air, as well as in the human diet. As MP is the main site of deposition after ingestion, the effects of ingested MP on the resident gut microbiota has become an area of interest, as well as the possibility that ingested MP contributes to the global obesity epidemic. This review highlights the existing research, which has implications in the connection between gut microbial dysbiosis and obesity-related metabolic dysfunction caused by exposure to MP. In animal studies, MP ingestion consistently leads to a decrease in the diversity of gut microorganisms, an increase in the abundance of Gram-negative and pro-inflammatory bacteria and a disruption of gut barrier function, which all contribute to metabolic endotoxemia, low grade systemic inflammation and altered lipid metabolism. Co-released plastic chemicals such as phthalates and bisphenols are also endocrine disrupting chemicals and so-called obesogens, which promote adipocyte differentiation. Limited human studies suggest possible links between the presence of fecal MPs, consumption of plastic packaging in food and changes in gut microbes, and increased BMI and adiposity. There is significant uncertainty about the extent of exposure, cause of exposure, and dose-response relationships in humans. We describe these mechanistic pathways, review the human evidence base and the priority research areas to address, such as standardised methods for quantifying MPs and prospective human cohort studies, to help clarify the role of microplastics as a modifiable environmental risk factor for obesity.