Those who enjoy fish on such a regular basis have a 12 per cent lower risk of bowel cancer than those who eat less than one portion per week, experts say.

The finding related to all types of fish, though people who opt only for smaller portions of oily fish can also cut their risk of bowel cancer by 10 per cent.

The study included experts from the University of Oxford and the International Agency for Research on Cancer (IARC), and was published in the journal Clinical Gastroenterology and Hepatology.

It was funded by the World Cancer Research Fund (WCRF).

For the study, researchers examined the dietary habits of 476,160 people who had filled in food frequency questionnaires.

This included detail on their fish intake - including white, fatty, oily and lean fish.

Over an average follow-up of 14.9 years, 6,291 people developed bowel cancer.

The results showed that eating 359.1g of any fish per week led to a 12 per cent decreased risk of bowel cancer compared with eating less than 63.49g a week.

Meanwhile, people eating just 123.9g a week of oily fish, such as salmon and sardines, enjoyed a 10 per cent lower risk of bowel cancer.

A typical portion of fish is around 100g.

The team said fatty and oily fish is an extremely rich source of long-chain n-3 polyunsaturated fatty acids (n-3 LC-PUFA), which are believed to have a protective effect in the body and prevent inflammation.

Non-fatty fish also contains these fatty acid compounds.

"Our research shows that eating fish appears to reduce the risk of bowel cancer and should be encouraged as part of a healthy diet," Dr Marc Gunter, the lead researcher from the IARC, said.

"One downfall of the study is that dietary data collected from participants did not include information on fish oil supplement intake. This unmeasured fish oil supplementation may also have an effect on bowel cancer, so further studies will be needed to see if fish or fish oil influence bowel cancer risk."

"The biological reasons by which fish consumption potentially lowers risk are not fully understood but one of the theories include specific fatty acids such as omega-3, found almost exclusively in fish, being responsible for this protective effect via their anti-inflammatory properties," Dr Anna Diaz Font, head of research funding at the WCRF, said.

Australian Associated Press