Vegetarian Diet Linked to 40% Higher Colorectal Cancer Risk, Study Finds

A new study suggests that vegetarian and vegan diets may lower the risk of certain cancers while increasing the risk of colorectal and esophageal cancers. The findings highlight the complex relationship between dietary habits and cancer development, as more people have reduced meat consumption since processed meat was classified as a Group 1 carcinogen.

According to the UK's Daily Mail and other outlets on the 27th (local time), researchers from the University of Oxford's Nuffield Department of Population Health analyzed cancer risks for 17 types of cancer among approximately 52,700 participants, divided into five groups based on dietary habits ranging from meat-eaters to vegans.

Risk Reduced for Five Cancer Types

The study found that vegetarians had a 21% lower risk of pancreatic cancer and 9% lower risk of breast cancer compared to meat-eaters. Prostate cancer risk was 12% lower, kidney cancer 28% lower, and multiple myeloma, a type of blood cancer, 31% lower.

The researchers explained that vegetarians' typically higher intake of fruits, vegetables, and dietary fiber, combined with avoidance of processed meat, may have contributed to reduced risk for some cancers. The vegetarian group had the highest fiber intake and lowest alcohol consumption overall.

The World Health Organization classified processed meat as a Group 1 carcinogen in 2015. Processed meats such as bacon, ham, and sausages are known to increase colorectal cancer risk, and red meat has also been linked to elevated cancer risk.

Colorectal and Esophageal Cancer Risk Higher

However, the study also yielded unexpected results. Colorectal cancer incidence among vegetarians was approximately 40% higher than among meat-eaters. The risk of squamous cell carcinoma, the most common type of esophageal cancer, was nearly double.

Vegans also showed significantly higher colorectal cancer risk compared to meat-eaters. The researchers suggested calcium deficiency as a possible cause. Vegans' average daily calcium intake was approximately 590mg, falling short of the recommended 700mg.

Cancer Research UK has stated that calcium helps reduce colorectal cancer risk. One study found that drinking a large glass of milk daily could reduce colorectal cancer risk by approximately 17%. However, the researchers noted that additional large-scale studies are needed, as the number of colorectal cancer cases in the vegan group was limited.

"Vegetarianism Is Not a Cure-All"

Professor Tim Key, who led the study, said, "On the surface, the findings may appear contradictory, but they do not conflict with existing research on processed meat and colorectal cancer." He noted that the relatively low processed meat consumption among the meat-eating participants could be a variable.

"Reducing meat intake may help prevent cancer, but a vegetarian diet does not completely eliminate cancer risk," Professor Key said. "Vegetarians also need to manage nutrients that tend to be deficient through supplements or fortified foods."

Professor Tom Sanders, a nutritionist at King's College London who was not involved in the study, also urged cautious interpretation. "This is important research, but we must consider that the meat-eating group did not consume large amounts of meat," he said.

Experts advise maintaining a diet centered on whole grains, legumes, fruits, and vegetables while avoiding processed meat and limiting red meat consumption to help reduce cancer risk. They also emphasize the importance of checking for deficiencies in nutrients commonly found in animal products, such as calcium and vitamin B12.

The study findings were published in the British Journal of Cancer and the American Journal of Clinical Nutrition.