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Eating foods such as fish that are rich in omega 3 fats might help prevent the spread of prostate cancer to other parts of the body, scientists say.

Men face a much more dangerous form of the disease if tumour cells from the prostate gland migrate and invade other parts of the body such as bone marrow.

However, researchers have found that an omega 3 fat can inhibit invasion by prostate cancer cells in laboratory tests, which may reduce their ability to spread to secondary sites.

The results of the study are published in the British Journal of Cancer.

Omega 3 fats are found in so-called 'oily' fish such as salmon, mackerel and fresh tuna.

Previous studies have suggested that omega-3 fats have protective effects against cancer and heart disease.

The latest study, based at Manchester's Christie Hospital, suggests that a diet rich in omega 3 fats might protect men with prostate cancer from developing a more aggressive form of the disease.

The study focused on omega 3 and omega 6 - the two main groups of polyunsaturated fatty acids in our diet.

Both types have essential roles in keeping us healthy but the Manchester study found that they have very different effects on prostate cancer cells.

Researcher Dr Mick Brown said: "Omega 6 fats, found in vegetable oils, nuts and seeds, increased the spread of tumour cells into bone marrow. This invasion was blocked by omega 3 fats - the ones found in oily fish.

Lead researcher Noel Clarke: "Eating a diet with the right balance of omega-3 and omega-6 fats may well help to keep prostate cancer within the prostate gland where it may be monitored safely or more easily treated with surgery or radiotherapy."

"It is possible to have a healthy balance of these two types of fat - we only need about half as much omega 3 as omega 6 - that will still stop cancer cells from spreading."

Lead researcher Noel Clarke said: "Some tumours develop slowly in the prostate without producing symptoms and sometimes when symptoms do develop, it is because the cancer has already spread.

"Eating a diet with the right balance of omega-3 and omega-6 fats may well help to keep prostate cancer within the prostate gland where it may be monitored safely or more easily treated with surgery or radiotherapy."

Professor John Toy, of Cancer Research UK, added: "Diet is a factor in many types of cancer, but its potential role is not yet fully clear in prostate cancer. This research shows an effect in the laboratory.

"However, we would need large population studies to provide the needed evidence to say a change in diet could reduce prostate cancer cells from spreading.

"Cancer Research UK advises people to reduce their risk of cancer by eating a healthy diet, high in fibre, fruit and vegetables and low in red and processed meat.”

Prostate cancer is the most common male cancer in the UK. Every year, around 30,000 men are diagnosed with the disease and an estimated 10,000 men die from it.

The Food Standards Agency recommends men can eat up to four portions of oily fish a week.

The study was funded by the Association for International Cancer Research (AICR) and the Medical Research Council (MRC).