Loading ...

After diagnosis and treatment of prostate cancer, men who predominantly consumed plant-based diets had disease progression only half as often as men who did not follow this diet, according to a US cohort study. Should doctors recommend vegetarian or even vegan diets to their patients in this stage of the disease?

"Various studies have shown in small patient groups that the risk of prostate cancer decreases when animal products are avoided, or that individuals generally suffer less from cancer when they follow a vegetarian diet. However, the evidence has been mostly of poor quality," said Axel Merseburger, MD, PhD, director of urology at the University Hospital Schleswig-Holstein, in Lübeck, Germany.

"What makes this relatively high-profile published study interesting is that it examined whether diet is relevant for the recurrence of prostate cancer in over 2000 men with 6.5 years of follow-up after diagnosis," he continued. "This is a question that patients frequently ask us after surgery: If they can do anything to protect themselves from the disease recurring. And this study shows that eating more plants lowers the risk of progression. This information can be incorporated into counseling patients who inquire about it."

Secondary Prevention Effect

Vivian N. Liu, of the Department of Epidemiology and Biostatistics at the University of California San Francisco, and her colleagues also observed that the effects of diet have mainly been studied in the primary prevention of prostate cancer. "Less well-researched, however, is how a plant-based diet affects individuals after a prostate cancer diagnosis," she said.

The investigators analyzed this relationship in a subset of the CaPSURE study. Men with histologically confirmed, nonmetastatic prostate cancer (stage T3a) were enrolled in the CaPSURE study between 1999 and 2018. Between 2004 and 2016, they participated in a comprehensive survey on diet and lifestyle, which included a validated food frequency questionnaire (FFQ).

Based on this information, Liu and her colleagues calculated two indices that determine the proportion of plant-based food in the diet: The Plant-based Diet Index (PDI) and the healthful PDI (hPDI). The two indices differ in the evaluation of plant-based foods classified as healthy (whole grains, vegetables, nuts, and legumes) or unhealthy (fruit juices, sodas, refined grain products, and potatoes). The latter receive lower scores in the hPDI.

Chronic Diseases

The PDI and hPDI were developed in 2016 in three large cohort studies and have already been linked to the risks for diabetes, coronary heart disease, and overall mortality; a lower risk for fatal prostate cancer; and better quality of life in men diagnosed with prostate cancer.

In the current study, Liu and her colleagues investigated whether the two indices are also associated with the progression of prostate cancer (ie, recurrence, secondary treatment, bone metastases, and prostate cancer-specific mortality) and prostate cancer-specific mortality.

Lower Progression Risk

The 2062 participants were mostly White and had a median age of 65 years. A median of 31.3 months had elapsed between the diagnosis of prostate cancer and the completion of the FFQ. During a median follow-up of 6.5 years after completing the FFQ, 190 men had progression of prostate cancer, and there were 61 prostate cancer-specific deaths.

Men who consumed the most plant-based diets according to the PDI (ie, the highest quintile) had a 47% lower risk for disease progression than those in the lowest PDI quintile.

When using the hPDI to evaluate diet, the results were less clear. In the overall group of men, this index was not associated with the risk for disease progression. Only in patients with aggressive prostate cancer (Gleason score ≥ 7) was there a significant association. In this subgroup, the highest hPDI quintile was associated with a 55% lower risk for progression than the lowest hPDI quintile.

Liu and her colleagues concluded that a predominantly plant-based diet in men with prostate cancer could be associated with better prostate cancer-specific outcomes. "It may be beneficial to assess the diet of prostate cancer patients and offer nutritional counseling as needed to establish healthy eating habits and support well-being and overall health."

Animal Products Allowed

"What one should not infer from these results is that one must deprive oneself after a diagnosis of prostate cancer," said Merseburger, who also noted that the study did not examine either a vegan or a vegetarian diet. Even in the highest PDI quintile, participants consumed meat and dairy products.

"The data largely confirm what has already been shown in other studies, namely, that a Mediterranean diet with plenty of vegetables and fruits, healthy olive oil, fish, and not too much red meat is likely to be the most advantageous in terms of cancer diseases," Merseburger concluded.

This story was translated from the Medscape German edition using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.