Plant-Based Foods May Reduce Risk of Prostate Cancer Progression

• A new study found that following a plant-based diet may slow the progression of prostate cancer in people recently diagnosed with the disease.
• A plant-based diet focuses primarily on fruits, vegetables, legumes, nuts, and whole grains.
• The study didn’t establish causation, but one of the researchers said the association between plant-based diets and slower prostate cancer progression was “strong.”

Following a plant-based diet—or one primarily filled with fruits, vegetables, legumes, and whole grains–has been associated with a reduced risk of everything from type 2 diabetes to premature death. Now, a new study suggests that the eating plan may slow the progression of prostate cancer. 

The research, published in the journal JAMA Network Open, found a link between a plant-based diet and a reduced risk of localized prostate cancer worsening over time. People with prostate cancer who ate the most plant-based foods had the lowest odds of cancer progressing.¹

The research indicates that “consuming a primarily plant-based diet—and less animal-based food—after a prostate cancer diagnosis may be associated with better prostate cancer-specific outcomes,” study author Stacey A Kenfield, ScD, a professor of urology at the University of California, San Francisco, told Health. “A plant-based diet is one promising diet that a clinician could recommend that has been associated with lower risk of prostate cancer progression, and numerous other outcomes.”

Kenfield said it’s important to note that this is a cohort study, meaning it can only show a connection between plant-based diets and better prostate cancer outcomes; it doesn’t establish causation. However, she added, the association her team found was “quite strong.”

How Much May Following a Plant-Based Diet Reduce Prostate Cancer Progression?

The new study is a follow-up to research Kenfield and her colleagues conducted that found a link between a plant-based diet and a reduced risk of developing fatal prostate cancer, particularly in men under 65.

“The next step was to evaluate this dietary pattern, after diagnosis, in men with prostate cancer,” she explained. “These results complement the previous findings.”

Her team gathered data about 2,062 men with non-metastatic prostate cancer enrolled in the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) study, a longitudinal observational study of more than 15,000 men with prostate cancer. The men were treated at 43 different urology practices nationwide from 1999 to 2018. Their median age was 65, and 95% of them were White.

Participants completed a diet and lifestyle questionnaire at some point—the median timeframe was 31 months—after their diagnosis, and researchers followed up with them for around 6.5 years. During that period, the cancer progressed for 190 people, and 61 people died from it. 

The team found that the men who ate the largest quantities of plant-based foods showed a 47% lower risk of prostate cancer progression. Among 680 men who had at least medium-grade cancer as determined by a measure known as the Gleason grading system, those who ate the most plant-based foods had a 55% reduced chance of cancer worsening. 

There was no association between diet and cancer progression, however, for people with low-grade prostate cancer. 

Samuel Haywood, MD, a urological oncologist at Cleveland Clinic, told Health that the connection between plant-based diets and slower cancer progression may in fact be due to other healthy habits people who tend to choose plant-based foods also practice. But, he said, the data adds to existing evidence suggesting that plant-based diets may benefit prostate cancer patients.

“My patients often are asking about dietary and exercise interventions when they are diagnosed with prostate cancer,” Haywood said. “For patients who are motivated to make dietary modifications, this may provide some inspiration to explore a plant-based diet.”

What’s Behind the Diet’s Possible Effect on Prostate Cancer?

Haywood said research hasn’t pinpointed the mechanism behind plant-based foods’ potential influence on prostate cancer progression, but that there are a few factors that could be behind the relationship.

Many plant-based foods contain antioxidants and anti-inflammatory compounds, which may have cancer-fighting properties. The plant-based diet may also cause beneficial changes to the microbiome that may affect prostate cancer progression. And, Haywood added, “these diets can often be healthier than a conventional diet, such as lower in fats or processed foods.”

Then there’s the high fiber content, which may regulate glucose levels and promote satiety.

“Managing weight or losing weight will improve insulin sensitivity and reduce chronic inflammation,” Kenfield said. “Clinical evidence suggests an association between insulin resistance, chronic inflammation, and cancer.”

Which Foods Show Benefit?

While all plant-based foods pack a nutritional punch, Kenfield points to several that have been shown to be associated with better outcomes for prostate cancer patients. 

She said sources of vegetable fat, like nuts, avocado, and olive oil show promise, as does fish, cooked tomatoes, and cruciferous vegetables such as broccoli and cauliflower. 

Haywood said that while many foods have been suggested to be beneficial for prostate cancer, the “evidence for each individual component is not particularly strong, so it’s hard to push any individual food item for prostate cancer patients.”

Next Steps for Research

Kenfield acknowledged that future studies should examine the role plant-based diets may have on prostate cancer in a more racially and ethnically diverse population. She’d also like to see studies that focus on men with metastatic prostate cancer.

A randomized controlled trial—considered the gold standard in epidemiological research—would be necessary to assess whether plant-based diets cause better outcomes for cancer patients.

“In the meantime,” she said, “I hope we can confirm these findings in other ongoing observational studies, which would add to the limited data on this topic.”