Response to Oxford Cancer Study

A new pooled analysis in the British Journal of Cancer ⁽¹⁾ examined cancer incidence in more than 1.8 million people across nine prospective cohorts and followed participants for a median of 16 years.  Overall, the study found that vegetarian diets were associated with lower risks for several cancers, including breast, prostate, kidney and pancreatic cancers, as well as multiple myeloma.  

However, some media headlines have focused on two findings suggesting increased risk for certain cancers among non-meat eaters. It’s important to understand these results in context. 

The study is observational – it cannot show causation 

The research is a prospective observational study, meaning it identifies correlations between dietary patterns and cancer risk but cannot establish cause and effect. The authors emphasise that explanations for the higher risks seen in a few cancers are speculative, based on possible nutritional differences rather than proven mechanisms. 

The overall pattern favours vegetarian and vegan diets 

Compared with meat eaters, vegetarians in this analysis showed: 

• 21% lower risk of pancreatic cancer
• 9% lower risk of breast cancer
• 12% lower risk of prostate cancer
• 28% lower risk of kidney cancer
• 31% lower risk of multiple myeloma  

These findings are consistent with broader evidence that diets rich in vegetables, fibre, and whole plant foods can support cancer prevention. 

The two increased-risk findings are based on small numbers 

Two associations received attention in media coverage: 

• Higher risk of oesophageal squamous cell carcinoma in vegetarians
• Higher risk of colorectal cancer in vegans 

However, these findings come from very small numbers of cases in the vegetarian/vegan groups, which the researchers note limits certainty. For example, the oesophageal cancer result was based on only 31 vegetarian cases across three studies, meaning statistical estimates are unstable and should be interpreted cautiously.  

Processed meat intake in the comparison group was relatively low 

Professor Tim Key, one of the study’s investigators, also noted that the findings should not be interpreted as contradicting the well-established link between processed meat and bowel cancer. 

He explained that many of the meat-eaters in the cohorts were relatively health-conscious and consumed modest amounts of processed meat. If the comparison group had included more people with high processed-meat intake, the differences in bowel cancer risk between dietary patterns might have been larger. 

This is consistent with existing evidence linking higher consumption of processed meat with increased colorectal cancer risk. 

Possible nutrient explanations remain hypotheses 

The authors suggested that some results might relate to lower intakes of specific nutrients in some vegetarian populations. Examples discussed in the paper include: Calcium intake (lower in some vegan diets) as a possible factor in colorectal cancer risk; Riboflavin (vitamin B2) or other micronutrients as possible factors for oesophageal cancer risk.  

Importantly, these were hypotheses rather than proven causes. 

The cohorts reflect diets from the 1990s and early 2000s 

Many participants were recruited between 1980 and 2010, with follow-up spanning decades.  

This means the study largely reflects earlier generations of vegetarian diets, when plant-based food options were more limited,  fortification of  vegan products was less common, and awareness of micronutrient supplementation was lower.  

Today’s plant-based diets – especially in the UK and Europe – include many fortified foods and supplements, making micronutrient deficiencies far less likely. 

The key message: Diet quality matters 

The findings reinforce an important point widely recognised in nutrition science that any dietary pattern – vegetarian or omnivorous – needs to be well planned. 

A balanced vegetarian or vegan diet that includes whole grains, legumes, fruits and vegetables, nuts and seeds, and appropriate fortified foods or supplements can meet nutritional requirements and support long-term health, and has been evidenced to have lower risk for many cancers.

Bottom line 

This study adds to the evidence that diets centred around plant foods are associated with lower risk for several cancers. The few increased-risk signals reported are uncertain, based on small numbers, and may relate to historical nutrient intakes rather than vegetarian diets themselves. r someone you know might benefit from attending a course, let us know at hello@vegsoc.org, or on social media.  

(1) Oxford Study