A new study in Circulation performed a systematic review of literature on the effects of different dietary habits. A larger summary of the results can be found on Science Based Medicine.
The study found that the consumption of processed meats, not red meats, increased the risk of coronary heart disease by 42%.
In a comparison of dietary habits, the study found that:
…in comparison with regular meat eaters, mortality from ischemic heart disease was 20% lower in occasional meat eaters, 34% lower in people who ate fish but not meat, 34% lower in lactoovovegetarians, and 26% lower in vegans.
There were no significant differences between vegetarians and nonvegetarians in mortality from cerebrovascular disease, stomach cancer, colorectal cancer, lung cancer, breast cancer, prostate cancer, or all other causes combined.