Plant-based fats improve long-term survival for prostate cancer patients

Men diagnosed with nonmetastatic prostate cancer can generally expect to live for many years after their diagnosis. However, cardiovascular disease and other cancers remain important threats to their long-term health. For many survivors, this raises an important question: What can I do to live a longer, healthier life? A new study published in JAMA Network Open suggests that the type and source of dietary fat they consume may make a difference.

The study, co-led by researchers from the Research Institute of the McGill University Health Centre (The Institute) and Harvard T.H. Chan School of Public Health, included nearly 5,000 men with nonmetastatic prostate cancer and followed them for a median of 12.8 years, drawing on data collected over more than three decades. The researchers found that the type and source of fat consumed after diagnosis were associated with long-term survival. Higher saturated fat intake, as well as higher animal fat consumption (a major dietary source of saturated fat), were associated with greater all-cause mortality. These associations were driven primarily by deaths from cardiovascular disease and, to a lesser extent, other cancers-not by prostate cancer itself.

Our findings suggest that diet after diagnosis may be one modifiable component of survivorship care, broadening the focus beyond control of the original tumor. Protecting cardiovascular and overall health is an essential part of prostate cancer care, particularly because some treatments can affect metabolic and cardiovascular health."

Lorelei Mucci, co-senior author, professor of epidemiology, Harvard Chan School

The findings are particularly relevant as the population of prostate cancer survivors continues to grow. Approximately 300,000 men are living with prostate cancer in Canada, while 3.5 million prostate cancer survivors live in the U.S. Supporting long-term health after diagnosis is therefore an increasingly important aspect of prostate cancer care. 

The source and type of fat matter

During follow-up, 3,040 participants died. The researchers' analysis showed that men with the highest saturated-fat intake had a 24% higher rate of death during follow-up than those with the lowest intake. Their estimated 10-year risk of death was 26.4%, compared with 23.4% among men with the lowest intake-a difference of about three deaths per 100 men over 10 years.

The researchers also used statistical models to estimate the potential impact of replacing certain dietary fats with healthier alternatives while keeping overall calorie intake similar. Replacing about 10% of daily calories from animal fat with plant-based fat was associated with a 16% lower rate of death from any cause. Similarly, replacing about 5% of daily calories from saturated fat with monounsaturated fat was associated with a 20% lower rate of death. 

"The central message is not simply to 'eat less fat.' Rather, the type and source of fat appear to matter. Replacing some animal fats and saturated fats with plant-based and unsaturated fats may help support long-term health after a prostate cancer diagnosis," said co-senior author David P. Labbé, scientist in the Cancer Research Program at The Institute and associate professor in the Department of Surgery at McGill University.

The findings are also consistent with studies in people without cancer and with dietary recommendations from the American Heart Association. However, the authors stressed that the study shows associations and does not establish cause and effect. The findings should not be interpreted as a recommendation to follow a restrictive diet or eliminate animal products altogether.

"The takeaway is to prioritize simple substitutions-choosing olive oil, nuts, seeds, avocados and other plant-based foods more often instead of foods high in animal or saturated fat," said co-senior author Edward Giovannucci, professor of nutrition and epidemiology at Harvard Chan School.

A large prospective study spanning more than three decades 

The study used data from the Health Professionals Follow-Up Study, a long-running prospective study that began in 1986 and has followed more than 50,000 male health professionals across the U.S. 

The researchers identified 4,884 participants diagnosed with nonmetastatic prostate cancer between 1986 and January 2019, most of whom were white and were approximately 70 years old at the time of diagnosis. Participants completed detailed, validated food-frequency questionnaires every four years and were followed through December 2022. 

The researchers examined whether the participants' intake of saturated, monounsaturated, polyunsaturated, trans, animal and plant-based fats was associated with overall mortality or specific causes of death. In their analysis, they accounted for many factors that could influence survival, including age, tumor stage and grade, treatment, smoking, physical activity, body weight and other health conditions. 

Of the 3,040 deaths during follow-up, 803 were from cardiovascular disease, 499 from cancers other than prostate cancer, and 441 from prostate cancer.

Toward personalized nutrition in prostate cancer care 

Since the study participants were predominantly white men in the U.S., the researchers hope to replicate their findings in more diverse populations. In addition, they plan to further investigate the role of diet after a prostate cancer diagnosis and examine specific foods, individual fatty acids, and broader dietary patterns, as well as whether the associations between fat consumption and health outcomes differ according to the treatment patients receive.

"Ultimately, our goal is to make nutrition a more precise and evidence-based component of prostate cancer care-one that takes into account the treatment received, tumor biology, and each patient's cardiovascular and metabolic health," said Labbé.