Flaxseed May Interfere With Estrogen Synthesis, Lower Risk of Breast Cancer

May 1, 1995

TORONTO, Canada--Researchers have discovered that a high-fiber grain cultivated since the times of the ancient Egyptians may delay the growth of cancerous tumors. In studies conducted on rats, Lilian Thompson, PhD, of the University of Toronto, found that a component isolated from flaxseed reduced mammary tumor growth by more than 50%.

TORONTO, Canada--Researchers have discovered that a high-fibergrain cultivated since the times of the ancient Egyptians maydelay the growth of cancerous tumors. In studies conducted onrats, Lilian Thompson, PhD, of the University of Toronto, foundthat a component isolated from flaxseed reduced mammary tumorgrowth by more than 50%.

Presenting her work at the annual meeting of the American Associationfor Cancer Research, Dr. Thompson said that flaxseed, also knownas linseed, helps the body to produce animal lignans--diphenolic,small-molecule compounds that can affect hormone levels and haveantioxidant and antitumor effects.

Plant Foods Tested for Lignan

Dr. Thompson and her team tested 66 different high-fiber grains,fruits, and vegetables for plant lignans, or lignan-like compounds,that the body can convert into usable animal lignans. She choseflaxseed because "it contains 75 to 800 times more lignanthan any other plant food."

Flaxseed also contains an oil rich in alpha-linolenic acid, whichis known to have anticancer effects. To determine the active ingredientthat suppresses the growth of mammary tumors, Dr. Thompson fedflaxseed and/or secoisolariciresinol diglycoside (SD), the majoranimal lignan precursor extracted from flaxseed, to rats 13 weeksafter they had been injected with a mammary carcinogen.

Dr. Thompson reported that after just 7 weeks, tumors in the animalsthat had received either flaxseed and/or the SD lignan grew atless than half the rate of the tumors in the control animals thatdid not get supplements. She also found that there were fewerand smaller new tumors in the group that received lignan.

"Lignan has characteristics that are similar to estrogen,"Dr. Thompson said. She suspects that flaxseed lignan interfereswith estrogen, limiting the body's ability to synthesize and reabsorbthe hormone. She also surmises that lignan may inhibit the growthof blood vessels in the tumor, thus starving the tumor.

Despite the favorable data, Dr. Thompson warned that the resultsare preliminary and that the study was done only on laboratoryanimals. Flaxseed is found in some multi-grain breads, and milledflaxseed is a component of some breakfast cereals. But she cautionedthat it would not be a good idea for women to eat huge amountsof flaxseed. Like all high-fiber foods, it ferments in the colonand may cause gas. In addition, she said, "you don't haveto eat lots to get a benefit because there is so much lignan inflaxseed already."

The University of Toronto, in collaboration with Paul Goss, MD,at Toronto Hospital, has begun dietary intervention trials in100 women with breast cancer, Dr. Thompson said. They hope toreport the results by the end of this year.

Dr. Thompson's work is bolstered by a new study that confirmsthe widely held belief that high-fiber, low-fat diets help reducebreast cancer. Lovell Jones, PhD, of M.D. Anderson Cancer Center,reported at the meeting that women following such diets have lowerlevels of nonprotein-bound, free estrogen in their bodies.

Dr. Jones studied 56 postmenopausal, low-income, African-American,Hispanic, and Caucasian women. They were taught by a dietitianhow to lower the fat in their diet and increase their fiber intake,and then were monitored for 1 year.

Dr. Jones found that when the women cut their fat intake to 20%of calories, free estrogen in the blood decreased, and increasedfiber in the digestive system increased the rate of estrogen eliminationfrom the body.

He also noted that differences in estrogen levels as a resultof ethnicity disappeared after the women went on the diet, suggestingthat diet, and not genetic background alone, plays a key rolein the development of breast cancer.