Diet Changes Show Promise in Early Prostate Cancer
A diet high in omega-3 and low in omega-6 fatty acids, alongside fish oil supplements, may curb the growth of prostate cancer cells in men with early-stage disease, new data showed.
Among men on active surveillance for prostate cancer, consuming this diet for a year led to a significant decrease in the prostate cancer tissue Ki-67 index, a biomarker for prostate cancer progression, metastasis, and death, according to findings from the phase 2 CAPFISH-3 study presented at the 2025 American Society of Clinical Oncology Genitourinary Cancers Symposium.
“This data is certainly intriguing and supports studies looking at this further in prostate cancer,” Bradley Alexander McGregor, MD, from the Dana-Farber Cancer Institute, Boston, who wasn’t involved in the study, told Medscape Medical News. But, McGregor noted, patients were on the diet for 1 year, and the long-term implications of this diet are not known.
Growing Evidence on Diet
Diets that include fried and processed foods tend to be high in omega 6s, while those that include salmon and tuna are higher in omega 3s.
Research has shown that consuming more omega-3 fatty acids is associated with a lower risk for mortality from prostate cancer, explained study investigator William Aronson, MD, with David Geffen School of Medicine at University of California, Los Angeles (UCLA). Research suggests that ingesting more omega-6 accelerates the growth of human tumors in mice, while raising omega-3 levels lowers it. High omega-3 and low omega-6 are also known to have an inhibitory effect on M2-like macrophages, which are the predominant immune cell type in prostate cancer metastasis.
To investigate the impact of these fatty acids on early-stage prostate cancer, Aronson and colleagues conducted a single center, phase 2, randomized, open label study in 100 men with grade 1/2 prostate cancer who elected active surveillance.
Patients were randomly allocated 1:1 to a control group that continued their normal diet (minus fish oil) or to an intervention group that followed a low omega-6/high omega-3 diet, supplemented with fish oil (2.2 g/d), for 1 year.
The primary endpoint was the change in Ki-67 index from baseline to 1 year from same site biopsies between the groups.
For the primary endpoint, the Ki-67 index decreased in the intervention group by 15% from baseline to 1 year and increased in the control group by 24%. The difference between groups was statistically significant (P = .043).
For the secondary endpoints, the intervention led to a reduction in triglyceride levels and macrophage colony stimulating factor but no change in tumor volume grade group, PSA level, or Decipher 22 gene score.
Aronson said the findings support future phase 3 trials incorporating this intervention among men on active surveillance for prostate cancer.
McGregor said it’s important to note that this was “an aggressive intervention with dietary changes and addition of fish oil and patients need to be highly motivated.” Four men discontinued due to side effects — primarily gastrointestinal side effects such as diarrhea and nausea — larger sample sizes will be key to better understand the tolerability.
Bottomline, said McGregor, “based on this data alone, it should not be recommended but can be considered for highly motivated patients after discussion of the limitations of available data and side effects.”
The study was funded in part by the National Cancer Institute, the UCLA Health Jonsson Comprehensive Cancer Center, Howard B. Klein, and the Seafood Industry Research Fund. Aronson disclosed relationships with AstraZeneca, Bayer, Blue Earth Diagnostics, Janssen Oncology, and Pfizer/Astellas. McGregor disclosed relationships with Arcus Biosciences, Astellas Pharma, Bristol Myers Squibb, Daiichi Sankyo/AstraZeneca, Eisai, Exelixis, Genmab, Gilead Sciences, Loxo/Lilly, Pfizer, and Seattle Genetics/Astellas.
