Studying microplastics in humans is still new. There are in fact a few studies that roughyl support atsur’s allegation(based on a pubmed search for “microplastics obesity”). These studies don’t have plastic acting as fat but rather that plastic causes signaling for fatty acid synthesis and reduction of lipolytic signaling. So basically plastics signal for you to be fat and can make it harder to lose fat.
Very minimal human data and not much that looks at direct cause-effect but there is at least a correlation that bears consideration.