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Evidence Explorer · MS-N295 · Nutrition and dietary patterns · Appraised November 10, 2026

CAPFISH-3 found a small between-group difference in prostate-tissue Ki-67 after one year. It found no difference in grade group, tumor length, genomic score or PSA, and four participants stopped because of fish-oil-related adverse events.

Evidence at a glance

  • Population: 100 men with grade-group 1 or 2 prostate cancer choosing active surveillance.
  • Intervention: a high-omega-3, low-omega-6 diet plus fish-oil capsules for one year versus control.
  • Primary result: Ki-67 fell from 1.34% to 1.14% in the intervention group and rose from 1.23% to 1.52% in control; the between-group change was statistically significant (P=.043).
  • Clinical findings: no significant differences in grade group, tumor length, Decipher score or PSA.
  • Evidence label: positive biomarker result; progression, metastasis and survival benefit not established.
  • Evidence label: Positive proliferation-biomarker result; clinical benefit unproven.

What was studied

Same-site prostate biopsies were compared at baseline and one year. The biological endpoint was selected because Ki-67 reflects proliferation, but it remains a surrogate in this setting.

The intervention bundled diet change with fish-oil capsules, so the trial cannot tell whether any biomarker effect came from lower omega-6 intake, higher food omega-3 intake, the supplement, weight or another behavior.

What this evidence cannot establish

The phase II study had a modest sample, the primary P value was close to .05, and multiple clinical secondary measures were negative. Active-surveillance progression and treatment-free survival require larger and longer trials.

Safety and practical context

Four participants were withdrawn for fish-oil-related adverse events. Fish oil can cause gastrointestinal symptoms and has antiplatelet effects; anticoagulant monitoring may be relevant. High-dose omega-3 products have also been associated with a small atrial-fibrillation increase in cardiovascular trials. Formulation and dose matter.

Questions for the care team

  • Am I interested in a tissue biomarker or an outcome that changes how long I can safely remain on surveillance?
  • What exact fish-oil dose and formulation was used, and does it interact with anticoagulants or surgery?
  • How will standard PSA, MRI and biopsy surveillance continue regardless of diet?

Sources and identifiers

Funding and conflicts: Funding and conflict details were not fully verified from the accessible abstract. The exact capsule formulation and dose should be taken from the full protocol before any clinical replication.

Source access and dates: Primary reports, registries and official guidance available through the links above were checked November 10, 2026. Last literature search November 10, 2026. Fields unavailable from accessible full text are labeled not reported or not verified rather than assumed absent.

Educational evidence summary, not individualized medical advice. Restrictive diets or supplements should not replace established cancer treatment or adequate nutrition. Symptom, weight, biomarker, laboratory, imaging, pathology or animal findings do not by themselves establish tumor control, recurrence prevention or longer survival.