Cancer risk is lower for vegetarians but not vegans, study finds

[LONDON] Vegetarian diets are linked with a lower risk of several cancers, including pancreatic, breast and prostate, according to a study that found no similar benefit – and even a higher chance of colon cancer – among vegans.

Researchers found people on vegetarian diets had a lower risk of five cancers compared with their meat-eating counterparts, though vegetarians had nearly double the risk of a cancer in the oesophagus called squamous cell carcinoma. The pioneering study, published on Friday (Feb 27) in the British Journal of Cancer, looked at pooled data from more than 1.8 million people across three continents.

The findings come at a time of renewed focus on diet after the US President Donald Trump’s administration updated US nutrition guidelines with an emphasis on animal-based protein. Concerns around the impact of ultra-processed foods, which the study did not look at, are also growing in the US and globally.

Though the study did not probe the cause of a higher or lower risk of certain cancers, researchers hypothesised that diets higher in fruit, vegetables, fibre and without processed meat could lower risks. The lack of meat is likely to be the reason for the different risk, according to Tim Key, emeritus professor of epidemiology at Oxford Population Health and co-investigator of the study.

Perhaps the biggest surprise was the finding for vegans. Red meat intake has long been associated with bowel cancer, yet vegans – who eat no meat or dairy – had a higher risk of this cancer in the study.

That may have been because many of the meat eaters in the study only ate moderate amounts of processed meat, according to the researchers. There were also relatively few overall cases of colon cancer among the vegans.

Still, the researchers said dairy might hold the key. “We are postulating that it could be because vegans have no dairy intake,” said Yashvee Dunneram, first author of the study. “Their calcium intake are really low in this consortium.”

The reduction in key vitamins and minerals might also be in play when it comes to the significantly higher risk among vegetarians of squamous cell carcinoma. “It may be related with a low intake of riboflavin,” said Aurora Perez Cornago, principal investigator of the study, while stressing that this was just a hypothesis. Riboflavin, also known as vitamin B2, is found in foods such as beef liver, eggs, fortified cereals, and milk.

Vegetarians in the study did have a lower risk of pancreatic, breast, prostate, kidney and multiple myeloma. One possible factor is weight. The vegetarians in the study had a lower body mass index, and while the researchers adjusted for this in the results, they hypothesised that this weight difference could still be behind the lower risk of breast cancer, for example.

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People on pescatarian diets, meaning they eat seafood and dairy but do not eat meat, also showed a lower risk of colon, breast and kidney cancer in the study.

One thing missing from the study was a comparison to a diet based on guidelines from the UK’s National Health Service, where meat and fish are consumed but only in moderation.

That provides important nutrients and may be the optimum diet for reducing the risk of diet-associated cancer, according to Jules Griffin, director of the Rowett Institute at the University of Aberdeen, who was not involved in the study. BLOOMBERG