At least one recent study implicated red meat consumption as a cause of type 2 diabetes. Dr. Richard Feinman at his blog takes a close look at the 2013 study and points out the great difficulty in making the leap from red meat to diabetes. I think Dr. Feinman’s point is best made by his graph about half way through the post, showing steadily decreasing red meat consumption as T2 diabetes takes off over the last four decades. (I assume all the figures are based on U.S. data.)
For the opposing viewpoint, read the original study (linked at Dr. F’s blog) or search at Fanatic Cook.
If red meat causes diabetes, it might make existing diabetes worse.
Do I worry that red meat causes diabetes? Not much. I await definitive research.