The grouping of two studies featured more than 61,000 people over a timespan of 12 years and found they contracted less cancer, independent of factors such as smoking, alcohol use and obesity than those who consumed meat or fish or both.
Differences in stomach and bowel cancer rates were not as pronounced as may have been expected given previous research and indeed, vegetarians had slightly higher, but not significantly so, rates of colon and rectum cancer.
Cervical cancer rates were twice that of meat-eaters among vegetarians. Breast and prostate cancer rates were similar, although there was less risk for prostate cancer among fish eaters than meat eaters.
Participants were drawn from a pool of British men and women who were either meat eaters and/or fish eaters or vegetarians. Of the total study population, 3,350 were diagnosed with one or more of the twenty cancers the researchers tested for.
They noted that 33 out of a hundred meat eaters will develop some form of cancer but only 29/100 non-meat eaters.
For some cancers such as multiple myeloma, which strikes bone marrow, vegetarians were 75 per cent less likely develop the condition.
Cancers of the blood and lymph such as leukemia and non-Hodgkin lymphoma were 50 per cent less likely in vegetarians than carnivores.
More study required
"More research is needed to substantiate these results and to look for reasons for the differences," said lead researcher, Tim Key, from the Cancer Research UK epidemiology unit at Oxford University.
"At the moment these findings are not strong enough to ask for particularly large changes in the diets of people following an average balanced diet."
The researchers said the reasons for lower cancer rates among vegetarians were not clear but suggested it could be down to viruses and mutation-causing compounds found in meat such as N-nitroso which are thought to damage DNA.
The temperatures at which meats are cooked could also produce damaging carcinogens.
The study population contained 15 571 men and 45 995 women, one third of whom were vegetarian.
Levels of physical activity were higher in vegetarians and fish-only eaters than in meat eaters, who also had higher body mass indexes (BMIs).
But the researchers said none of the findings were conclusive despite some evidence linking, for instance, high intake of fruit and vegetables and onset rates of some cancers.
“There is also some evidence that a high intake of fruit and vegetables might reduce the risk for stomach cancer, but the data are not consistent and, although on average vegetarians eat more fruit and vegetables than meat eaters, the difference in intake is modest,” they wrote.
British Journal of Cancer
(2009) 101, 192–197. doi:10.1038/sj.bjc.6605098
‘Cancer incidence in British vegetarians’
Authors: TJ Key, PN Appleby, EA Spencer, RC Travis, NE Allen, M Thorogood and JI Mann