The study, published in the journal BMC Medicine and co-funded by World Cancer Research Fund and Cancer Research UK, saw Oxford University researchers analyse data from 472,377 British adults taking part in the UK Biobank study between 2006 and 2010.
Participants, who were between 40 and 70, were asked about their dietary habits – including how much and how regularly they eat meat or fish.
It found those who consumed a small amount of meat have a two per cent lower risk of cancer, compared to those on meat-heavy diets.
Pescatarians – people who eat fish and vegetables – were found to be at a reduced risk of 10 per cent, while vegetarians were 14 per cent likely to develop cancer.
People who do not eat a lot of meat had a nine per cent lower risk of developing bowel cancer compared to near eaters.
Vegetarian women were 18 per cent less likely to develop postmenopausal breast cancer.
The risk of developing prostate cancer was 20 per cent lower in men who stuck to a pescatarian diet, while it was 31 per cent lower in vegetarians.
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Researchers were able to come to this conclusion by tracking the health records of participants for up to 11 years to see whether not they went on to develop cancer.
During this spell, 55,000 cases of cancer were identified.
Lead researcher Cody Watling, from Oxford Population Health’s Cancer Epidemiology Unit, said: “Previous evidence has suggested that vegetarians and pescatarians may have a lower risk of developing cancer, however the evidence for a lower risk of developing specific types of cancer has been inconclusive.
“Being overweight after menopause is known to increase the risk of breast cancer and so the reduced risk of postmenopausal breast cancer in vegetarian women, due to lower BMI, was unsurprising – but we were surprised by the substantially lower risk of prostate cancer in vegetarians.”
Dr Giota Mitrou, director of research and innovation at World Cancer Research Fund International, said: “One in two of us will get cancer in our lifetime and while there are lots of things about cancer we cannot control, we know that currently 40% of cancer cases could be prevented through lifestyle changes including diet, weight and physical activity.
“The results of this large, British study suggest that specific dietary behaviours such as low meat, vegetarian or pescatarian diets can have an impact on reducing the risk of certain cancers: in this case bowel, breast and prostate.”
Dr Julie Sharp, head of health and patient information at Cancer Research UK, said: “Maintaining a healthy diet is a great way to lower your risk of cancer and eating less processed meat reduces your risk of bowel cancer, specifically.
“But more research is needed to understand the link between red and processed meat and other cancer types.
“Having some bacon or ham every now and then won’t do much harm. If you are having a lot of meat a lot of the time, then cutting down is a good idea, but a vegetarian diet doesn’t always mean someone is eating healthily.
“It’s more important to have a balanced diet with lots of fruit, vegetables and high fibre foods, like wholegrains and pulses, and low in processed and red meat and foods high in salt, sugar and fat.”