That may be a problem, but it wouldn’t explain the differences in results due to sponsorships.

It’s a very interesting topic. But it’s really hard to study in humans. Due to the abundance of microplastics everywhere, it’s almost impossible to conduct controlled trials. It’s rather unethical to inject humans with plastic and cutting them open to look inside is also frowned upon (rightfully so). We can compare with historical measurements, but then, of course, we can’t isolate the effects of microplastics.