It was too good to be true: a study by Mayo Clinic researchers finds that flaxseed doesn’t help prevent hot flashes after all.
Doctors had hoped flaxseed could be a safer alternative for hot flash relief for women than hormone-replacement therapy, which effectively eases menopausal symptoms but increases the risk of breast cancer and heart attack.
Because flaxseed contains phytoestrogens, plant compounds that mimic the effect of estrogen in the body, the thinking was that it could compensate for the loss of the hormone during menopause — the change that triggers hot flashes and other symptoms.
(More on TIME.com: Making Sense of Hormone Therapy After Menopause)
Back in 2007, a small pilot study of 29 women by the same Mayo researchers had suggested that consuming 40 grams of crushed flaxseed a day helped reduce hot flashes. Many women who use flaxseed also say it helps.
But the initial Mayo study didn’t compare flaxseed to a placebo, so there was no way to know whether the women’s symptoms were simply resolving on their own over time or whether they were benefiting from the placebo effect or whether the flaxseed was actually helping.
For their new research, the Mayo scientists created a randomized controlled trial, assigning 188 women with hot flashes (due to either menopause or breast-cancer treatment) to eat a fiber bar that contained either 40 g of flaxseed or no flaxseed for six weeks. Both groups recorded their hot flashes daily in a diary.
The researchers found that in both groups, a third of the women reported a 50% decrease in hot flashes — which suggests that flaxseed works no better than a placebo and that hot flashes get better on their own.
(More on TIME.com: Why Those Agonizing Hot Flashes May Not Be All Bad)
“There were so many testimonials that we thought flaxseed was going to work, but a testimonial is not a rigorous clinical trial result, and that’s what our patients deserve,” Dr. Mark Kris, a cancer specialist at Memorial Sloan-Kettering Cancer Center, told the Washington Post.
Both groups also reported symptoms of bloating, diarrhea and nausea, which may be attributed to the fiber in the bars, says study author Sandhya Pruthi of the Mayo Clinic.
Women still have other options to combat the symptoms of menopause. Antidepressants, such as Effexor and Zoloft, have been shown in studies to help alleviate hot flashes.
(More on TIME.com: Antidepressants May Relieve Hot Flashes)
In addition, Pruthi says women don’t have to stop taking flaxseed, especially if they enjoy it. Flaxseed has other benefits, including managing the digestive system.
The study was presented during the American Society of Clinical Oncology Annual Meeting.