Vegetarians have a lower risk of five cancers - but a higher risk of one rare one

Scientists have conducted the largest study to date that compares the risk of different types of cancer in people with different types of diets, from meat-eaters to vegans. The analysis included data from 1.8 million participants from 9 long-term observational studies in the UK, USA, Taiwan and India. People were tracked for about 16 years on average.

The researchers divided the participants into five groups:

• "meat-eaters " (eat red and/or processed meat),

• "poultry eaters" (no red or processed meat, but poultry),

• pescetarians (eat fish but no meat or poultry),

• vegetarians (no meat or fish, but with dairy products and/or eggs),

• vegans (no animal products of any kind).

What was found in vegetarians

Compared to meat-eaters, vegetarians were found to have a lower risk of five types of cancer:

• pancreatic cancer - 21 per cent lower,

• breast cancer, 9 per cent lower,

• prostate cancer 12 per cent lower,

• kidney cancer 28 per cent lower,

• multiple myeloma (a type of blood cancer) 31 per cent lower.

But there was an important exception: vegetarians were found to have almost twice the risk of oesophageal squamous cell cancer (which is a type of oesophageal tumour).

What about vegans

Vegans showed a statistically significant higher risk of colorectal cancer (bowel cancer) - about 40 per cent higher than meat-eaters. No clear differences were found for other cancers, but the authors emphasise: vegans had fewer cases, so there is not yet enough data on rare diagnoses.

Other "non-meat" groups

• Pescetarians had lower risks for bowel cancer, breast cancer and kidney cancer.

• Those who ate poultry but avoided red/processed meat had a slightly lower risk of prostate cancer.

Why this might be the case

The authors suggest that vegetarians tend to have more fruit, vegetables and fibre and less processed meat - this may reduce the risks of some tumours. And the increased risk of some cancers in vegetarians/vegans may be due to deficiencies in certain nutrients that are easier to get from animal foods (e.g. B12, calcium, etc.) - but the reasons still need to be clarified.

However, the study is observational: it shows a link, but does not prove that diet directly "causes" a reduction or increase in risk - other lifestyle factors may also influence the results.