Increased Vegetable Intake Fails to Slow Prostate Cancer Progression, Study Finds

By Sally Robertson, B.Sc.Jan 14 2020

Researchers in the United States have conducted a study investigating whether a telephone-based interventional program encouraging an increased intake of vegetables would slow disease progression among patients with early-stage prostate cancer.

Image Credit: Alexander Raths/Shutterstock.com

Although the behavioral intervention did increase the men’s consumption of micronutrient-rich vegetables for two years, it did not produce any significant delay in disease progression, compared with control patients who received only written information about diet and prostate cancer.

The data from this study fail to support clinical guidelines and media claims suggesting that increased vegetable consumption may improve clinical outcome for patients with prostate cancer.

Previous studies and current guidelines

Some studies have indicated that eating certain foods can slow disease progression among prostate cancer survivors and many men want to know whether following a particular diet might help or even cure their cancer.

Guidelines that circulate widely in the public domain endorse vegetable-enriched diets as a way of improving outcomes among this patient group. The recommendations, which are based on preclinical studies, observational data and expert opinion propose that such a diet may decrease disease progression and even death among this patient group.

Randomized clinical trials are needed

Indirect evidence suggests that consumption of micronutrient-enriched plants may promote genomic stability, induce expression of cytoprotective enzymes, and decrease the risk of lethal prostate cancer, but data from randomized clinical trials focused on actionable clinical endpoints are lacking,”  

J. Kellogg Parsons (University of California, San Diego Moores Comprehensive Cancer Center)

The team says that trials showing the effectiveness of vegetable enriched diets in slowing disease progression would justify the development of behavioral interventions encouraging prostate cancer patients to adopt such diets.

The majority of patients present with early-stage prostate cancer and choose active surveillance (where they are monitored with prostate-specific antigen (PSA) testing and follow-up biopsies) over immediate treatment with surgery or radiation. However, at least one-third of these patients experience disease progression or undergo definitive treatment within two years of follow-up.

Interventions that prevent disease progression would decrease the need for treatment and improve the quality of life among these patients and diet modification represents one potential approach to achieving this.

What did the current study involve?

To investigate whether a behavioral intervention designed to increase micronutrient-enriched vegetable intake among men with early-stage prostate cancer was effective at preventing disease progression, Parsons and team conducted a phase 3 study called The Men’s Eating and Living (MEAL) Study.

This randomized clinical trial was conducted at 91 urology and medical oncology clinics and involved 478 men, aged 50 to 80 years, diagnosed with early-stage prostate adenocarcinoma, who were on active surveillance.

Patients were randomly assigned to receive a motivational telephone-based behavioral counseling encouraging consumption of at least 7 daily servings of vegetables (intervention group, n=237) or written information about diet and prostate cancer (control group, n= 241.)

The men were enrolled between January 2011 to August 2015 and were followed up over two years from January 2013 to August 2017.

The findings failed to support the use of the intervention

As reported in JAMA, the intervention did produce robust and sustained increases in the men’s consumption of carotenoid-, cruciferous-rich and leafy green vegetable for two years. However, there was no significant difference in time-to-disease-progression between the intervention and control groups.

“These data fail to support prevailing assertions in evidence-based clinical guidelines and the popular media that diets high in micronutrient-enriched vegetables improve cancer-specific outcomes among prostate cancer survivors,” writes the team.

“The findings do not support the use of this intervention to decrease prostate cancer progression in this population,” they conclude.