[throwaway_4ever]

Does the study prove causality though? By what physical mechanism does a range of different substances, with no calories, cause diabetes and cardiovascular problems?

The glaring problem is that diet sodas are often consumed as part of an unhealthy diet, alongside unhealthy fast food burgers and fries, and that best explains why you'd see the increase in diabetes and cardiovascular issues. Occam's razor.

[hansvm]

One possible mechanism is that by tasting something sweet you respond hormonally the same as if you had consumed sugars, increasing pancreatic workloads. There's a fair bit of research showing that diet sodas increase hunger, so it isn't too far-fetched to believe something causal exists in there.

The study by itself doesn't really prove causality though.