By Biplab Das
Phytoestrogens (isoflavones and lignans), a type of plant chemicals found in legumes (soy), grains, seeds, nuts, fruits and vegetables may curtail the risk of colorectal cancer, reports a Canadian research team.
Phytoestrogens are present in the plant as glycosidic conjugates, a type of complex organic compounds. After ingestion through diet, enzymes and bacteria in the gastrointestinal tract convert the phytoestrogens into other compounds and further metabolism takes place in the systemic circulation of human body.
The two major phytoestrogen classes found in food are isoflavones and lignans. Isoflavones are found in small amounts in a number of legumes, grains and vegetables, but soybeans are by far the most concentrated source of isoflavones in the human diet. Lignans, on the other hand, are present in a wide variety of plant foods, including seeds (flax, pumpkin, sunflower, poppy), whole grains (rye, oats, barley), bran (wheat, oat, rye), fruits (particularly berries) and vegetables. Actually lignans enter human body through diet as lignan precursors - pinoresinol, lariciresinol, secoisolariciresinol, and matairesinol, which are converted into mammalion lignans - enterodiol and enterolactone, by the action of intestinal bacteria.
In recent years, scientists have become interested in the activities of isoflavones and lignans as both mimic the activities of estrogen, a signalling molecule, better known as hormone and implicated in hormone-associated cancers (breast, prostate, uterine and ovarian). Isoflavones and lignans can bind to estrogen receptors (protein molecules that sit on the cell membrane), mimicking the effects of estrogen in some tissues and blocking the effects of estrogen in others.
Studies have shown that soy isoflavone supplementation may decrease arterial stiffness. Isoflavones are also thought to prevent hormone-associated cancers like breast, uterine and prostate. Studies show that isoflavone could prevent osteoporosis and hot flushes among women receiving treatment for breast cancer. Lignans have also been shown to reduce the risk of uterine (among postmenopausal women only) as well as ovarian cancers.
The Canadian team investigated the association between dietary phytoestrogen intake (isoflavones, lignans and total phytoestrogens) and colorectal cancer risk among cases (aged 20-74 yrs) and controls (age and sex matched with cases) participating in the population-based Ontario Familial Colorectal Cancer Registry (OFCCR). The OFCCR is 1 of 6 international sites participating in the Cooperative Familial Registry for Colorectal Studies established by the U.S. National Cancer Institute.
Of all the cases and controls approached, 1095 cases and 1890 controls completed epidemiological (colorectal screening, medical conditions, medication use, diet, reproductive factors, physical activity, sociodemographics, and anthropometric measures) as well as food-frequency questionnaires. Daily phytoestrogen intake was determined based on FFQ (food-frequency questionnaire), which asked about foods eaten about two years ago. And 842 cases and 1251 controls gave blood samples for tracking any genetic roles in phytoestrogen metabolism and incidence of colorectal cancer.
The Canadian researchers found that higher dietary lignan intake was linked to considerable reduction in colorectal cancer risk. Dietary isoflavone could also reduce the risk of colorectal cancer. They also found a link between higher phytoestrogen intake (lignans and isoflavones combined) and reduced risk of colorectal cancer. No significant roles of genes were found in association between phytoestrogen metabolism and colorectal cancer risk.
Other research groups also reported similar results on phytoestrogens’ roles against colorectal cancer. An Italian research team reported that increased intake of isoflavones could decrease the risk of colorectal cancer. Studies with human colon cancer cells (SW480) have shown that lignans thwart the growth of tumor cells driving them to commit mass suicide (apoptosis).
In the US , colorectal cancer is the third most common cancer and the third leading cause of cancer related mortality. According to the National Cancer Institute, in 2007, 112,340 new cases of colon cancer and 41,420 cases of rectal cancer have been detected with 52,180 deaths from colorectal cancer (colon and rectal combined). Besides the loss of lives, every year around $8.4 billion is spent for the treatment of colorectal cancer in the US .
According to the Canadian and other research teams, increase in the intake of dietary phytoestrogens could reduce the risk of colorectal cancer.
The Canadian study was published in the Journal of Nutrition on the December 2006 edition.**
**Michelle Cotterchio, Beatrice A. Boucher, Michael Manno, Steven Gallinger,Allan Okey,
and Patricia Harper. Dietary Phytoestrogen Intake Is Associated with Reduced Colorectal Cancer Risk. Journal of Nutrition, December 2006: Vol 136: 3046–3053.
Hongyan Qu, Ronald L. Madl, Dolores J. Takemoto, Richard C. Baybutt and Weiqun Wang. Lignans Are Involved in the Antitumor Activity of Wheat Bran in Colon Cancer SW480 Cells. Journal of Nutrition. March 2005: Vol 135, 598-602.
Marta Rossi, Eva Negri, Renato Talamini, Cristina Bosetti 1, Maria Parpinel, Patrizia Gnagnarella, Silvia Franceschi, Luigino Dal Maso, Maurizio Montella, Attilio Giacosa and Carlo La Vecchia. Flavonoids and Colorectal Cancer in Italy . Cancer Epidemiology Biomarkers & Prevention. August 2006: Vol. 15, 1555-1558.
Colerectal cancer, National Cancer Institute, US National Institute of Health.
Lignans, Linus Pauling Institute, Oregon State Univeristy
Isoflavones, Linus Pauling Institute, Oregon State University
A Snapshot of Colorectal Cancer, National Cancer Insitute, US