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Plant-Based Diets and Prostate Cancer
Two new studies suggest benefits of plant-based diets on prostate cancer risk, outcomes

“Plant-based” foods are increasingly on the radar. You can grab a green juice at most chain coffee shops, a decent salad at airport restaurants, or a meat-free veggie burger at some locations of the major burger chains. And at many local grocery stores or farmers’ markets, you can purchase ingredients to cook a veggie-based meal.

Research shows many benefits of a plant-based diet, especially for overall and heart health. For example, in looking across multiple studies, vegetarians were found to have a 9% lower risk of death overall, 29% lower risk of death from heart disease, and 18% lower risk of cancer vs. non-vegetarians. Now, two new papers authored by PCF-funded researchers report benefits of plant-based diets for prostate cancer.

A plant-based diet may reduce risk of developing or dying from prostate cancer

What is a plant-based diet?Defining a plant-based diet can be challenging: it ranges from vegan (eating no animal products) to vegetarian (eating no fish, chicken, or other meat) to semi-vegetarian (eating little fish or meat). Not all plant-based foods are considered equal: think of chips and soda vs. a kale salad. To better define the gradations and quality of these various diets, some studies use a plant-based diet “index,” (or score) based on how often a person reported eating certain foods over the previous year. Foods were categorized as healthy plant-based (e.g., whole grains, vegetables, nuts), less-healthy plant-based (e.g., fruit juices, refined grains, desserts), and animal group (e.g., dairy, eggs, meat).

A team including PCF-funded investigators Dr. Stacy Loeb and Dr. Stacey Kenfield reviewed multiple studies to address this question. The studies asked participants about their diet, followed them for many years, and counted the number of prostate cancer cases and deaths from prostate cancer. There was some variation in the definition of the diet (see Sidebar); generally, vegetarians/vegans were compared to nonvegetarians. Overall, the authors reported that a plant-based diet was linked to either a decreased risk of prostate cancer or had no effect on risk.

Aligned with these findings, a study authored by Drs. Loeb and Kenfield, along with PCF-funded scientists Dr. Lorelei Mucci and Dr. June Chan followed more than 47,000 health professionals over 28 years. Investigators computed three different dietary scores for each participant: overall plant-based, healthful plant-based, and unhealthful plant-based (see Sidebar). Key results included:

  • Eating a more plant-based diet overall was linked to lower risk of fatal prostate cancer. Men with the highest plant-based diet score had a 19% lower risk of fatal prostate cancer vs men with the lowest diet score.
  • Eating a healthful plant-based diet was linked to a lower risk of being diagnosed with localized prostate cancer.
  • Some effects of diet differed by age. For example, among men under age 65 at diagnosis, eating a more plant-based diet was linked to a 42% lower risk of advanced prostate cancer.

Dr. Mucci presented some results of this study in a PCF webinar which can be viewed here.

How might a plant-based diet be protective against some types of prostate cancer? The authors suggest a number of possible biological effects, such as greater consumption of anti-oxidant and anti-inflammatory compounds that are naturally present in fruits and vegetables.

A plant-based diet may improve outcomes among patients with prostate cancer

Clinical trials of plant-based diets have focused on two groups of men with prostate cancer: those with low-risk disease on active surveillance, and those with biochemical recurrence after initial treatment. For example, the Prostate Cancer Lifestyle Trial randomized 93 men with low-risk prostate cancer to a one-year intensive lifestyle program including a very low-fat vegan diet, regular exercise, stress management, and a support group. Patients in the control group received usual care. After one year, patients in the intervention group had significantly lower PSA levels vs the control group. After two years, significantly fewer patients in the intervention group had gone on to have prostate cancer treatment (2) vs in the control group (13). Patients in the lifestyle intervention group also experienced other health benefits, such as reduced weight, cholesterol, and perceived stress.

Trials of a plant-based diet (coupled with stress reduction) in patients with recurrent prostate cancer showed an increase in PSA doubling time, which may suggest less aggressive cancer. These studies were small, with short follow-up time. While these findings are promising, more research is needed.

 What this means for patients: If you’ve been thinking about adopting a more plant-based diet–maybe swapping out some meat and dairy for more fruits, veggies, and whole grains–these studies suggest that may help lower your risk of certain types of prostate cancer, or of prostate cancer progression. Consult your doctor or a nutritionist about any major dietary changes, especially if you’re in treatment or have other health conditions. Download PCF’s wellness guide, The Science of Living Well, Beyond Cancer, for more nutrition and lifestyle tips.

What is a plant-based diet?Defining a plant-based diet can be challenging: it ranges from vegan (eating no animal products) to vegetarian (eating no fish, chicken, or other meat) to semi-vegetarian (eating little fish or meat). Not all plant-based foods are considered equal: think of chips and soda vs. a kale salad. To better define the gradations and quality of these various diets, some studies use a plant-based diet “index,” (or score) based on how often a person reported eating certain foods over the previous year. Foods were categorized as healthy plant-based (e.g., whole grains, vegetables, nuts), less-healthy plant-based (e.g., fruit juices, refined grains, desserts), and animal group (e.g., dairy, eggs, meat).
Becky Campbell
Becky Campbell develops medical content at the Prostate Cancer Foundation. She has previously worked in outcomes research and in science education.

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