A recent study released at the European Gastroenterology Week 2025 (UEGWeek2025) event suggests that microplastics (plastic particles less than 5 millimeters commonly found in the environment) can alter the human gut microbiota, with some changes resembling patterns associated with depression and colorectal cancer. This study is one of the first to directly examine how different types of microplastics interact with the human gut microbiota. This study used fecal samples from 5 healthy volunteers for in vitro cultivation of gut microbiota. Subsequently, these cultures were exposed to five common microplastics - polystyrene, polypropylene, low-density polyethylene, polymethyl methacrylate, and polyethylene terephthalate. Their concentrations reflect estimated human exposure levels and are exposed to higher doses to study potential dose-dependent effects. Although the total number of bacterial cells and the number of viable bacterial cells remained relatively unchanged, the acidity of the culture treated with microplastics continued to significantly increase compared to the control group, indicating a change in microbial metabolic activity. Further analysis shows that there have been microplastic specific changes in bacterial composition, with the number of certain bacterial populations increasing or decreasing depending on the type of microplastic. The changes observed in several bacterial families mostly occur within the phylum Bacillus. The Bacillus phylum is a key group of intestinal bacteria that is crucial for digestion and overall intestinal health. The changes in the composition of these bacteria are accompanied by changes in the chemicals produced by the bacteria, some of which correspond to the observed increase in acidity. Some types of microplastics alter the levels of valeric acid and 5-aminovaleric acid, while others affect lysine or lactate, highlighting the complexity of microplastic microbiota interactions. Importantly, some of these microplastic induced changes in microbial composition reflect patterns previously associated with diseases such as depression and colorectal cancer, highlighting the potential impact of microplastic exposure on disease risk. (New Society)