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MS-N165 · Food-based botanical · Hot-flash support · Women with or without breast-cancer history · Double-blind phase III trial · Appraised 28 October 2026

Does a daily flaxseed lignan bar reduce hot flashes in postmenopausal women, including women with a history of breast cancer?

Evidence at a glance

  • Evidence label: Negative phase III trial
  • Benefit: Hot-flash scores fell in both groups, but flaxseed was not significantly better than placebo.
  • Certainty: Moderate. The trial was randomized and blinded, enrolled 188 women and used prospective diaries, but mixed women with and without breast-cancer history.
  • Risk: Gastrointestinal symptoms were common in both groups. Fiber can worsen bloating or constipation and, without adequate fluid, rarely contribute to obstruction.

What was studied

Postmenopausal women with at least four daily hot flashes were randomized to one bar daily containing flaxseed with 410 mg lignans or a matched placebo bar for six weeks. Current use of tamoxifen, a SERM or aromatase inhibitor was a stratification factor. The primary endpoint was change in hot-flash activity from baseline to the final treatment week.

What the evidence found

Mean hot-flash score fell 4.9 points with flaxseed and 3.5 with placebo; the between-group difference was not significant (P=0.29; 95% CI for the comparison −0.7 to 3.5). Slightly more than one-third in each group achieved a 50% score reduction. Abdominal distension, flatulence, diarrhea and nausea occurred in both groups.

How to interpret it

The placebo response matters. An earlier uncontrolled pilot looked encouraging, but this blinded comparison did not confirm benefit. The result concerns hot flashes, not breast-cancer recurrence or survival, and it does not test flaxseed oil or other lignan doses.

Practical safety context

Discuss concentrated lignan products with the oncology team, particularly with bowel narrowing, severe constipation, swallowing difficulty or multiple oral medicines. Take fiber with adequate fluid unless fluid restriction applies. Food-based flaxseed and high-dose extracts are not interchangeable.

Questions for the care team

  • Is the goal hot-flash relief or general dietary fiber?
  • Do I have bowel symptoms or medicines that make extra fiber difficult?
  • Which evidence-based nonhormonal hot-flash options fit my treatment?

Funding and conflicts

Supported through North Central Cancer Treatment Group/NCI grants. The accessible full report did not identify a commercial efficacy interest.

Sources

Last literature search: 28 October 2026. Record appraisal: 28 October 2026. This page is educational and does not replace individualized medical advice. Symptom, biomarker or observational findings must not be interpreted as proof of tumor control, recurrence prevention or longer survival unless those outcomes were directly tested.