Is there really a link between what we eat every day and the risk of developing cancer? Science has been circling around this for years, often with studies too small to say anything definitive. Now, however, research has arrived that cannot be ignored so easily.
The University of Oxford coordinated an analysis of more than 1.8 million people, published in British Journal of Cancer and built thanks to the work of the Cancer Risk in Vegetarians Consortium, an international project that brought together data from nine large epidemiological studies conducted in Europe, the United States and Asia. The participants were followed for about sixteen years — long enough to observe the possible onset of oncological diseases over time.
The sample included omnivores, people who ate only poultry, pescatarians, vegetarians and vegans. In total, the researchers examined more than seventeen types of cancer, from the gastrointestinal system to the lungs, from the urinary tract to the reproductive system, to blood cancers. And they also took into account other factors, such as body weight, smoking and general lifestyle, to make the results more precise and less influenced by external variables.
A detail worth underlining: much of the data collected dates back to the 1990s and early 2000s. Since then the world of nutrition has changed a lot. Vegetable products fortified with calcium and vitamins are much more widespread today, and ultra-processed food has conquered an increasingly larger share of our daily habits.
Lower risk for pancreas, prostate, breast, kidney and multiple myeloma
The data is clear on this point. Compared to regular meat consumers, those who follow a vegetarian diet are 21% less likely to develop pancreatic cancer, 12% less prostate cancer, 9% less risk of breast cancer, 28% less risk of developing kidney cancer and even 31% less risk of multiple myeloma, a form of blood cancer that affects plasma cells.
Numbers that are not far-fetched. Plant-based diets generally contain more fiber, more fruits and vegetables, and a greater amount of plant bioactive compounds that participate in the regulation of inflammation, metabolism, and cell growth. Some researchers also hypothesize a role of lower levels of the hormone IGF-1, a molecule involved in cell growth processes and studied for years for its possible link with the development of some neoplasms.
The relationship between what we put on our plates and our health, however, is never as simple as we would like. Diet is just one of many factors that interact with genetics, lifestyle and the environment in which we live.
The unexpected results
Here comes the part that made even the authors of the research raise an eyebrow. Vegetarians are almost twice as likely to develop esophageal squamous cell carcinoma, the most common form of esophageal cancer. A possible explanation concerns the insufficient intake of some B vitamins, more present in foods of animal origin.
Even more controversial is the data regarding vegans: in this group the risk of colorectal cancer is approximately 40% higher than in meat consumers. A result that has a plausible explanation: the average calcium intake in the vegans analyzed was around 590 milligrams per day, while in the United Kingdom the recommended amount is 700 milligrams daily. Not a huge difference, but potentially significant in the long run.
The authors are quick to contextualize: contemporary vegan diets often include fortified foods that significantly improve the intake of key nutrients, and today’s nutritional landscape is very different from that of the 1990s captured by the data in this study. Furthermore, the consumption of red and processed meat in the omnivore group analyzed was relatively low compared to other more recent cohorts. According to Professor Tim Key, epidemiologist emeritus of the University of Oxford and one of the authors of the research, a greater presence of heavy consumers of red meat would probably have changed the final result.
The other dietary models analyzed also offer interesting ideas. Pescetarians show a lower risk of breast, kidney and colon cancer. Those who eat only poultry have a lower risk of prostate cancer. Data that suggests how even a simple reduction in the consumption of red and processed meat can have an impact on cancer prevention, even without completely eliminating animal proteins.
What emerges from the Oxford research, ultimately, is a more complex picture than expected. The large sample size analyzed — a huge advantage compared to previous studies, often too small to draw conclusions about rarer cancers — opens up new avenues for prevention and research. The authors are the first to underline that further investigations are needed to precisely understand the biological mechanisms at play. But in the meantime, the numbers speak.
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