For a review published in 2023 in the journal Environmental Pollution, researchers examined E171 as a possible factor promoting obesity-related metabolic disorders. Because gut microbiota play an important role in immune function maintenance and development, and because titanium dioxide as a food additive has been shown to alter gut microbiota, researchers wanted to review “the dysregulations along the gut microbiota-immune system axis after oral TiO2 exposure compared to those reported in obese or diabetic patients, and to highlight potential mechanisms by which foodborne TiO2 nanoparticles may increase the susceptibility to develop obesity-related metabolic disorders.” The study authors discovered recurrent changes in the gut microbiota composition when exposed to titanium dioxide nanoparticles, with an imbalance of intestinal symbiotic microbiota. These changes and imbalances were also reported and played a role in the development of obesity, the authors wrote. This highlights “foodborne TiO2 nanoparticles as an endocrine disruptor-like chemical promoting obesity-related disorders,” the authors concluded.

How we’re exposed to an ingredient matters greatly in terms of our long-term health. 
  
Research shows that inhaling titanium dioxide particles in significant quantities over time can cause adverse health outcomes. Unless you work in an industrial setting, inhaling substantial amounts of titanium dioxide is highly unlikely.