Vegetarian and Vegan Diets: A Surprising Look at Cancer Risks
For years, many Australians have been reducing their red meat consumption, largely driven by the persistent belief that it’s a significant contributor to bowel cancer. However, a landmark, large-scale study has delivered a rather unexpected finding: vegetarians don’t necessarily have lower rates of bowel cancer than meat-eaters, and, surprisingly, vegans might actually face a higher risk of developing such tumours.
This revelation, described as “very surprising” by experts, suggests that certain vegetarian and vegan diets might be lacking in essential nutrients. While the study doesn’t definitively prove that veganism causes bowel cancer, it does prompt a re-evaluation of dietary assumptions. It’s important to note that limiting red meat is still generally advised, particularly for cardiovascular health.
A Deeper Dive into the Study’s Findings
The comprehensive research, spearheaded by Oxford University, also uncovered some positive news for vegetarians, linking their dietary choices to a reduced risk of five other types of cancer. This contrasts with the historical view of red meat, once lauded for its rich vitamin, mineral, and protein content, but increasingly scrutinised in recent decades due to its saturated fat and its suspected link to bowel cancer. Similar concerns have been raised about processed meats like sausages and bacon, primarily based on observational studies showing correlations between their consumption and higher cancer rates.
The Enigma of Red Meat and Cancer
While the exact mechanisms are still being explored, animal studies have indicated that compounds present in red and processed meats could contribute to the formation of harmful N-nitroso compounds (NOCs) in the gut. Conversely, incorporating plant-based alternatives like beans into one’s diet is known to increase fibre intake, aiding digestion and potentially offering protection against bowel cancer.
Current Australian health guidelines, mirroring those in the UK, recommend limiting red and processed meat consumption to an average of no more than 70 grams per day. For context, a typical serving of mince for spaghetti bolognese might be around 100 grams. Many institutions, including schools and local councils, are actively encouraging a shift towards plant-based foods, citing both health and environmental benefits.
However, the scientific evidence directly linking red and processed meat to cancer has remained inconclusive. The long latency period for such effects makes it challenging to conduct definitive randomised controlled trials, the gold standard in medical research. Scientists typically rely on observational studies, which can be susceptible to biases. For instance, individuals who choose vegetarian or vegan lifestyles often exhibit other healthy behaviours, such as avoiding smoking and excessive alcohol, which researchers attempt to account for in their analyses.
Key Findings from the Global Study
This latest research consolidated data from nine observational studies worldwide, including five from the UK, encompassing the dietary habits and cancer rates of 1.8 million individuals over a 16-year follow-up period. Participants were categorised into groups: meat-eaters, those who avoided red meat but consumed poultry, fish-eaters, vegetarians, and vegans. Their rates of 17 different cancers were meticulously tracked.
No Significant Differences for Most Cancers: For the majority of the cancers studied, no discernible difference in rates was observed between vegans, vegetarians, and individuals consuming any type of meat.
Benefits for Vegetarians: A notable finding was that vegetarians exhibited a slightly lower risk for five specific cancers compared to meat-eaters:
- Multiple myeloma (a blood cancer): 31 per cent lower risk.
- Kidney cancer: 28 per cent lower risk.
- Pancreatic cancer: 21 per cent lower risk.
- Prostate cancer: 12 per cent lower risk.
- Breast cancer: 9 per cent lower risk.
Dr. Aurora Pérez-Cornago, the lead researcher and formerly an associate professor at the University of Oxford, highlighted these findings as positive for vegetarians, particularly given the prevalence of some of these cancers.
Surprising Risks for Vegetarians and Vegans: The study also revealed some unexpected associations:
- Oesophageal Cancer Risk for Vegetarians: Vegetarians had a significantly higher risk (93 per cent) of developing cancer of the gullet (oesophagus). Dr. Pérez-Cornago noted this was a novel finding, warranting further investigation due to its strong association in this study.
- Bowel Cancer: No Benefit, Higher Risk for Vegans: Perhaps the most striking outcome was the absence of any protective effect against bowel cancer for vegetarians, challenging established medical thinking. Professor Jules Griffin, head of the Rowett Institute at the University of Aberdeen, described this as a “major surprise.” Furthermore, the study indicated that vegans had a 40 per cent higher risk of bowel cancer compared to meat-eaters, a finding that contradicts the common perception of veganism as inherently healthier, according to Professor Tom Sanders, a former nutrition researcher at King’s College London.
Exploring the Nutritional Gaps
The questions arising from these findings are substantial: what could be responsible for the increased bowel cancer risk in vegans, the lack of benefit for vegetarians, and the elevated risk of gullet cancer among vegetarians? While this study did not delve into the specific mechanisms, experts have offered some hypotheses.
Professor Sanders suggests that vegans might be falling short on Vitamin B12, a nutrient crucial for nerve function and DNA synthesis. A deficiency could potentially lead to dysregulation of genes that normally control cell growth, a process implicated in cancer development.
Dr. Pérez-Cornago pointed to calcium as a potential factor in the bowel cancer findings. Calcium is believed to play a protective role by binding to bile acids in the gut, which can otherwise damage the intestinal lining and promote cancer. Vegans, by excluding dairy products, may have lower dietary calcium intake. However, she noted that modern dairy substitutes, such as oat milk, are often fortified with calcium, potentially mitigating this risk for contemporary vegans.
Beyond Cancer: Broader Health Implications
Regardless of cancer risks, reducing red meat intake likely offers other health advantages, such as improved heart health. However, individuals making this dietary shift must be mindful of ensuring adequate intake of essential vitamins and minerals, either through supplements or fortified foods.
Dr. Aisling Daly, a lecturer in nutrition at Oxford Brookes University, cautioned that if meat products are not replaced with nutritionally equivalent alternatives, the intended health benefits may not be realised.
The findings of this significant study were published in the British Journal of Cancer.
