The Western diet is characterized by higher intake of processed and red meats, high-fat dairy and refined grains.
The study, published in Cancer Prevention Research, was conducted by researchers from Harvard T.H. Chan School of Public Health and investigated the diets of 926 men diagnosed with prostate cancer for an average of 14 years after their diagnosis.
"There is currently very little evidence to counsel men living with prostate cancer on how they can modify their lifestyle to improve survival. Our results suggest that a heart-healthy diet may benefit these men by specifically reducing their chances of dying of prostate cancer," says senior author Jorge Chavarro, assistant professor of nutrition and epidemiology at the Harvard Chan School.
According to the authors of the study, prostate cancer is the most commonly diagnosed and second most lethal cancer for men in the US. The American Cancer Society (ACS) state that around 1 in 7 men will be diagnosed with prostate cancer during their lifetime.
The researchers write that, to date, only one study has evaluated the potential role of dietary patterns after prostate cancer diagnosis, concluding that adherence to a Mediterranean diet was not associated with prostate cancer-specific mortality.
For the study, data were obtained from the Physicians' Health Study I and II, trials of male physicians aged 40-84 in the US. Participants were sent food-frequency questionnaires to collect information on their diets.
Participants were grouped into quartiles based on whether they followed a Western dietary pattern or a "prudent" dietary pattern, involving a higher consumption of fruit, vegetables, fish, legumes and whole grains.
During the follow-up period, 333 participants died, with 56 of these deaths (17%) attributed to prostate cancer.
How might diet improve survivorship of prostate cancer?
The researchers found that those who ate a predominantly Western diet (those in the highest quartile) were two-and-a-half times more likely to die from prostate cancer and had a 67% increased risk of all-cause mortality compared with participants in the lowest quartile. In comparison, the men who follow a "prudent" diet closely had a 36% lower risk of all-cause mortality.
The researchers noted a number of other characteristics concerning the followers of the two particular diets. Those who scored highest for the "prudent" diet consumed less animal fat and alcohol and were more likely to have never smoked. Men scoring highest for the Western diet tended to be older at prostate cancer diagnosis and had lower intakes of calcium and vitamin D.
Lead author Meng Yang, a research fellow at the Harvard Chan School, states that their results are encouraging though it is important to keep in mind the limitations of the study. All the participants of the study were physicians and the majority of them were white.
"Therefore it is very important that our results are replicated in other studies with more diverse socioeconomic and racial/ethnic backgrounds," says Yang. Additionally, the study does not measure any potential confounders such as the physical activity of the participants and the forms of treatment they were receiving.
Despite these limitations, the authors believe their findings suggest that modifications to diet after prostate cancer diagnosis may influence survival and have a direct clinical impact for patients.
"Nevertheless, given the scarcity of literature on the relation between postdiagnostic diet and prostate cancer progression, and the small number of disease-specific deaths in the current study, these associations, particularly those for disease-specific mortality, merit caution in their interpretation as well as further evaluation," the authors conclude.