Drinking a daily eight ounce (0.24 litre) glass of pomegranate juice can significantly slow the progress of prostate cancer, a study suggests.
Pomegranates have been linked to many health benefits
Researchers say the effect may be so large that it may help older men outlive the disease.
Pomegranates contain a cocktail of chemicals which minimise cell damage, and potentially kill off cancer cells.
The study, by the University of California in Los Angeles, appears in the journal Clinical Cancer Research.
Previous research had indicated that pomegranate juice could have a beneficial effect on prostate cancer in tests on mice.
But the latest study has shown that humans can potentially benefit too.
The UCLA team focused on 50 men who had undergone surgery or radiation treatment for prostate cancer - but had shown signs that the disease was rapidly returning.
The presence of prostate cancer cells is monitored by measuring levels of a chemical they produce called prostate-specific antigen (PSA).
The researchers measured how long it took for PSA levels to double in individual patients - a short doubling time indicates that the cancer is progressing quickly.
The average doubling time is about 15 months, but in patients who drank pomegranate juice this increased to an average of 54 months.
Some men on the study continue to show suppressed PSA levels after more than three years, even though they are receiving no treatment apart from drinking pomegranate juice.
Lead researcher Dr Allan Pantuck said: "I was surprised when I saw such an improvement in PSA numbers.
"In older men 65 to 70 who have been treated for prostate cancer, we can give them pomegranate juice and it may be possible for them to outlive their risk of dying from their cancer.
"We are hoping we may be able to prevent or delay the need for other therapies usually used in this population such as hormone treatment or chemotherapy, both of which bring with them harmful side effects."
Pomegranate juice is known to have anti-inflammatory effects and high levels of anti-oxidants, which are believed to protect the body from damage by particles called free radicals.
It also contains isoflavones which are believed to play a role in cancer cell death.
Dr Pantuck said: "There are many substances in pomegranate juice that may be prompting this response.
"We don't know if it's one magic bullet or the combination of everything we know is in this juice.
"My guess is that it's probably a combination of elements, rather than a single component."
Chris Hiley, of the Prostate Cancer Charity, said more work was needed to firm up the findings.
She said: "It may well turn out that pomegranate juice has a wider application than just delaying disease progression in men with prostate cancer who have already been treated.
"It might also help as a reassuring low-key intervention for men whose cancer is being monitored rather than treated."
Dr Laura-Jane Armstrong, of the charity Cancer Research UK, said: "If the results of this study can be confirmed, it could have important implications for prostate cancer patients, especially by delaying the use of other more aggressive treatments that can have debilitating side effects."
Funding for the study was received from a company which makes pomegranate juice.