Could be a transient change in flora. You could try to keep eating it and see if the issue resolved, and if it doesn't after about two weeks you might have to consider that your body has changed.
I'm not sure if abstaining from red meat for two weeks would cause such a drastic shift, though, unless you were eating low quantities of protein or avoiding all meat. Even then, you might want to consider that red meat isn't necessarily the culprit here. Just going way out on a limb, I'd say there's a slight chance it could be related to low stomach acid.
Edit: reread your post and noticed you said months, not weeks. That makes it a little more possible. Since it's already been a couple of weeks since you started eating it again, try looking at other areas of your diet for changes you might have inadvertently made, including the types of red meat you eat and how you prepare it/what you eat it with
Edited by Quetzlcoatl, 24 April 2014 - 11:53 PM.