The Guardian article links to the paper, which has this in the introduction: Relative risks (RRs) were estimated by Cox regression, stratified by s

The Guardian article links to the paper, which has this in the introduction: Relative risks (RRs) were estimated by Cox regression, stratified by sex and recruitment protocol and adjusted for age, smoking, alcohol, body mass index, physical activity level and, for women only, parity and oral contraceptive use. I wouldn't disagree that there's still a lot of uncertainty, but at least for cancer, I'd bet on a small but significant effect. Anyway: what is pretty much proven is that living like a vegetarian is quite beneficial. You can probably even continue eating meat. (One possibly life-prolonging behaviour observed more in vegetarians: not considering the Guardian to be a 'sensationalist' newspaper)