The findings, which were reported at the 2023 ASCO Genitourinary Cancers Symposium in February, are based on a study of 2,038 men (median age, 64 years) with prostate cancer at stage T1, T2, or T3a.
“Consuming a whole foods plant-based diet may be an option to decrease risk for recurrence and improve overall survivorship,” said Vivian N. Liu, a clinical research coordinator at the University of California, San Francisco, who presented the findings.
The patients were interviewed about their diets at about 31.5 months after diagnosis. The study group was broken down into four groups based on how much of their diet consisted of a plant-based diet. Men in the highest quintile group who consumed at least 2.4 servings daily of fruit, 4.2 servings of vegetables, 2.6 servings of dairy, and 1.2 servings of meat (not seafood), had a 52% lower risk of progression (hazard ratio, 0.48; 95% confidence interval, 0.36-0.65; P-trend < 0.001) and a 53% lower risk of recurrence (HR, 0.47; 95% CI, 0.32-0.68; P-trend < 0.001), which was statistically significant. This compares with men in the lowest quintile who consumed 0.8 servings a day of fruit, 2.1 servings of vegetables, 3.1 servings of dairy, and 1.4 servings of meat. The findings were adjusted for total caloric intake, race, and smoking status.
For men over 65 years old, researchers found that a plant-based diet was associated with lower risk of recurrence (HR, 0.41; 95% CI, 0.24-0.7; P-trend = 0.03). And for those who exercised daily – in this case walking at a fast pace more than 3 times a week – a plant-based diet had a 56% (HR, 0.33; 95% CI, 0.26-0.73) lower risk of progression in the highest quintile group and a 59% decrease in recurrence (HR, 0.41; 95% CI, 0.25-0.68).
A new analysis like this, Ms. Liu said, “could guide people to make better, more healthful choices across their whole diet rather than adding or removing select foods.”
The primary endpoint was progression including recurrence, secondary treatment, bone metastases, and death due to prostate cancer, and the secondary endpoint was recurrence (PSA > 0.2ng/mL at 2 consecutive follow-up visits or during secondary treatment). At 7.4 years follow-up, there were 204 cases of progression.
“Fruits and vegetables contain antioxidants and anti-inflammatory components as well as dietary fiber that improve glucose control and reduce inflammation,” Ms. Liu said. In contrast, she said, animal-based foods may increase insulin resistance and insulin levels and boost levels of insulin-like growth factor 1, which is associated with prostate cancer risk. More studies, especially randomized controlled trials, are needed to provide evidence whether healthful plant-based foods and prostate cancer progression are connected.
NYU Langone Health urologist Natasha Gupta, MD, published a systematic review in 2022 on the impact of a plant-based diet on prostate cancer.* The review, which included 5 interventional studies and 11 observational studies, found that consuming a plant-based diet was associated with improvements in general health for men with prostate cancer. The observational studies found either a lower risk of prostate cancer or no significant difference.
“Patients often ask if there is anything that they can do to reduce the risk of recurrence, and it is great to be able to tell patients that a healthy lifestyle including plant-based foods and physical activity is helpful,” Dr. Gupta said.
The review’s coauthor, Stacy Loeb, MD, also of NYU Langone Health, said the new study was “a well-done observational study by experts in nutritional epidemiology from UCSF. It adds to a large body of evidence showing that plant-based diets improve health outcomes.”
“In the short-term, purchasing plant-based protein sources, such as beans and lentils, is less expensive than buying meat. Plant-based diets also reduce the risk of obesity, diabetes, and cardiovascular disease, which are associated with hundreds of thousands of dollars over a lifetime,” she said.
Limitations of the new study included the small number of non-White participants and self-reporting of diet. The study doesn’t examine the cost of various diets or the availability of plant-based foods like fresh produce, which can be limited in some neighborhoods.
Ms. Liu and colleagues plan to conduct a study that examines postdiagnostic plant-based diets in relation to prostate cancer–specific mortality. She and her team will also examine the plant-based dietary indices in relation to prostate cancer–specific quality of life at 2, 5, and 10 years from baseline.
The study authors, Dr. Loeb, and Dr. Gupta report no disclosures.
Correction, 3/17/23: An earlier version of this article misstated the name of NYU Langone Health.