Vegetarians have a substantially lower risk of five types of cancer, a landmark study on the role of diet has revealed.
The research, using data from more than 1.8 million people who were tracked over many years, found that vegetarians had a 21% lower risk of pancreatic cancer, a 12% lower risk of prostate cancer and a 9% lower risk of breast cancer compared with meat eaters. Combined, these cancers account for around a fifth of cancer deaths in the UK.
Vegetarians also had a 28% lower risk of kidney cancer and a 31% lower risk of multiple myeloma, according to the study published in the British Journal of Cancer.
Dr Aurora Pérez-Cornago, the principal investigator on the study, which was carried out while she was based at the University of Oxford, said: “This study is really good news for those who follow a vegetarian diet because they have a lower risk of five cancer types, some of which are very prevalent in the population.”
While being vegetarian appeared to be protective overall, the scientists also found that those who follow a vegetarian diet had nearly double the risk of the most common type of cancer of the oesophagus, known as squamous cell carcinoma, compared with meat eaters. This may be due to vegetarians being deficient in key nutrients such as B vitamins, the team suggested.
Vegans had a 40% higher risk of bowel cancer when compared with meat eaters. This may be due to the low average intake of calcium (590mg a day, compared with the UK recommendation of 700mg a day) and lower intakes of other nutrients.
The researchers said more work was needed to establish whether meat consumption was problematic or whether something specific in vegetarian diets lowers cancer risk – and the answer might vary depending on cancer type.
“My feeling is the difference is more likely to be due to the meat itself, but that’s an opinion that we haven’t looked at directly,” said Prof Tim Key, emeritus professor of epidemiology at the University of Oxford and co-investigator.
Although there is a known link between red and processed meat consumption and bowel cancer risk, until now it has not been possible to reliably assess the link between diet and less common cancers due to the typically low numbers of vegetarians and vegans included.
To overcome this, the latest study drew on data from various studies on diet and health from across the world. This allowed the researchers to compile data from about 1.64 million meat eaters, 57,016 poultry eaters (no red meat), 42,910 people who ate fish and no meat (pescatarians), 63,147 vegetarians and 8,849 vegans, who were followed for an average of 16 years. Factors that could influence cancer risk, such as body mass index and smoking, were taken into account.
The study, funded by the World Cancer Research Fund, investigated 17 different cancers, including those of the gastrointestinal tract, lung, reproductive system and urinary tract, and blood cancer.
There was no evidence for vegetarians having a lower risk of bowel cancer, compared with meat eaters. This is likely to be due to the intake of red and processed meat in the people in the study being relatively low compared with those included in more recent cohorts and, Key said, the findings were “not incompatible” with previous results highlighting the association between red and processed meat and bowel cancer.
“It could be that if we had had more people with very high intakes of meat in the meat-eating group, the results could have been different,” he added.
Pescatarians had lower risks of breast and kidney cancers, as well as a lower risk of bowel cancer. Poultry eaters were found to have a lower risk of prostate cancer.
The people in the studies were followed for an average of 16 years and, while this allowed the scientists to track cancer outcomes effectively, it also means that diets will have evolved since the 1990s and 2000s when many of the participants were first recruited. Ultra-processed food has become more widely consumed, for instance, and vegan products such as oat milk are now often fortified with calcium and other nutrients.
Prof Jules Griffin, director of the Rowett Institute, University of Aberdeen, who was not involved in the research, said the work was impressive. “What is missing in this study is a comparison to a group eating the NHS Eatwell guidelines, where meat and fish consumption is in moderation, but at the same time provides important nutrients to the diet – this may be the optimum diet for reducing risk in the population for diet associated cancer,” he added.
