Need an incentive to join Sir Paul McCartney’s "Meat Free Monday" campaign?

Here’s one: A British study has found that vegetarians have a lower risk of developing cancer than their carnivore colleagues.

The study, published in the British Journal of Cancer, followed 61,000 men and women for 12 years. Participants included 32,403 meat eaters, 8,561 “fish eaters” (they ate fish but no meat) and 20,601 vegetarians (no meat or fish). By the end of the study period, 3,350 people had been diagnosed with cancer. Of those, 68 percent (2,204) were meat eaters, 24 percent (800) were vegetarians and 9.5 percent (300) were fish eaters.

That meant that the vegetarians were 12 percent less likely to develop cancer than meat eaters. (For those of you quick at math, yes, the fish eaters did appear to fare even better than the vegetarians. Their risk was 18 percent lower. But because the number of fish eaters was so small, that statistic is not considered as reliable.)

For certain cancers, the difference in risk between meat and non-meat eaters was quite striking. For non-Hodgkin’s lymphoma and multiple myeloma (cancer of the bone marrow) the risk for vegetarians was about 45 percent lower than for meat eaters. Their risks for bladder and stomach cancer were also lower.

But there was one piece of bad news for vegetarian women: Their risk for cervical cancer was almost double that of meat eaters. This finding may have been the result, the study’s authors suggest, of non-food-related factors, such as more vegetarian women getting screened — and, thus, diagnosed — for that cancer.

The study's limitations
Which brings me to the usual caveats for an observational study like this one. It relied on the dietary self-assessments of the participants, and those assessments can be unreliable. So, at best, this kind of study can only show an association between two things (diet and cancer) and not a cause-and-effect.

Also, both the vegetarians and the fish eaters in this study were slightly less likely to smoke and drink alcohol and more likely to engage in a high level of physical activity than the meat eaters. They also weighed slightly less. These factors — or others unknown — could also explain their lower cancer risk in this study.

Still, the findings are interesting, if far from conclusive. The study’s authors speculate (as many others have before them) that cancer-causing compounds or perhaps even viruses in meat may be behind these differences in risk. Another possible explanation: cancer-protective compounds in fruits and vegetables.

Of course, even if these results prove true, being a vegetarian isn’t a full-proof shield against cancer, as Paul McCartney, sadly, knows only too well. His first wife, Linda, an outspoken advocate for vegetarianism (and animal rights), died of breast cancer in 1998.