Caffeine can decrease insulin sensitivity in humans.
 

 http://www.ncbi.nlm.nih.gov/pubmed/11815511

Diabetes Care 2002;25:364-369.

 

ABSTRACT:

CONCLUSIONS:

Caffeine can decrease insulin sensitivity in healthy humans, possibly as a result of elevated plasma epinephrine levels. Because dipyridamole did not affect glucose uptake, peripheral adenosine receptor antagonism does not appear to contribute to this effect.