Highlights
Flaxseed, a popular functional superfood and a rich source of phyto-estrogen is known to have many health benefits. However, despite the large number of studies carried out across the world, the evidence on whether flaxseed intake is good for reduction of risk of breast cancer, prostate cancer or colorectal cancer is still inconclusive. Before consuming a flaxseed rich diet, cancer patients should also consult a nutritionist due to concerns regarding reduced platelet aggregation and other possible side effects and negative interactions.
Flaxseeds
Flaxseed meals, flaxseed muffins, flaxseed in juices and smoothies and flaxseed cereals are some of the variations of the functional super foods that have become a fad amongst the health conscious consumers today, for their multitude of health benefits. However, humans have been consuming flaxseed since ancient times. It has been cultivated for fiber as well as for medicinal purposes and as a nutritional product. (Tolkachev and Zhuchenko, Pharm Chem J, 2000) Flax seeds are rich in fiber, phyto-estrogen lignans and are a rich source of alpha-Linolenic acid (ALA), an essential omega 3-fatty acid. (Kajla P et al, J Food Sci. Technol, 2015)
Flaxseed oil has been used for a variety of health disorders including osteoarthritis, rheumatoid arthritis, breast cancer, prostate cancer, colon cancer, diabetes, obesity, cardiovascular diseases, hypertension, dry skin, dry eyes and many other conditions.
Nutritional Composition of Flax Seeds
Flaxseed has emerged as a popular functional food due to presence of three main bioactive compounds – alpha-Linolenic acid, fiber and phyto-estrogen, that have many potential health benefits. (Kajla P et al, J Food Sci. Technol, 2015)
It is a rich source of ALA, an essential polyunsaturated fatty acid that is reported to have anti-inflammatory properties and also key to maintaining the structural integrity of our cell membranes. Nutritionists globally suggest incorporation of omega 3-fatty acid sources in our diets and flaxseed serves as the best omega 3 fatty acid source for vegetarians.
Flaxseed is a rich source of phyto-estrogen (lignans). It contains high levels of proteins and very low levels of carbohydrates. Flaxseeds also contain phenolic compounds such as ferulic acid, chlorogenic acid and gallic acid, known for their anticancer and antioxidant properties. (Beejmohun V et al, Phytochem Anal., 2007) Flaxseeds are also good sources of minerals such as phosphorus, calcium, magnesium and contain the antioxidant Vitamin E.
Association Between Flaxseed Intake and the Risk of Different Types of Cancers
Below are examples of some of the studies associated with flaxseed intake and the risk of different types of cancers.
Flaxseeds and Breast Cancer Risk
Hormone driven breast cancer is one of the most common and highly prevalent subtypes of breast cancer in women. Estrogen is the key driver for hormone driven breast cancer. Since flaxseeds have a very high amount of phyto-estrogens (lignans) that are similar to estrogen, a natural concern is whether flax seeds are good and safe to use by breast cancer patients and if they could further increase the risk of breast cancer? This concern applies to other hormone linked cancers such as endometrial, uterine, ovarian, prostate cancers also.
There have been many studies that have been done to determine whether phyto-estrogens raise or lower the risk of developing breast and other hormone driven cancers. The results of the studies have been inconclusive. Some have found a decrease in risk with higher phyto-estrogen intake while others have found individual variations in benefits of cancer prevention.
- In a meta-analysis of multiple studies including randomized controlled trials, uncontrolled trials, biomarker study and observational studies of 1892 records, consumption of flax seeds was associated with a decreased risk of breast cancer. Flaxseeds showed reduced proliferation and growth in breast tissue of women at risk of breast cancer and may protect against primary breast cancer. They also found a reduced mortality risk with flaxseed consumption among those living with breast cancer. (Flower G et al, Integr Cancer Ther., 2014)
- In a population based study from the Ontario cancer registry, they found that total phyto-estrogen intake was associated with a reduction in risk of breast cancer but predominantly in women who were overweight. They found no statistically significant association among post-menopausal women and breast cancer risk. (Cotterchio M et al, Cancer Causes & Control, 2007)
- In another meta analysis of studies between 1997 and 2009 to determine association between phyto-estrogen intake and breast cancer risk, they found a reduced risk of breast cancer in postmenopausal women with higher intake of lignans. (Buck K et al, Am J Clin. Nutr., 2010)
- A pilot study including 24 postmenopausal women with Estrogen Receptor positive (ER+) breast cancer was done to study the interactions between effects of flaxseeds and an aromatase inhibitor drug used to treat breast cancer. The results indicated that using flaxseeds did not have any effects on the aromatase inhibitor activity based on selected breast cancer biomarkers and the hormone levels. (McCann SE et al, Nutr. & Cancer, 2014)
- A prospective cohort study including 58,049 postmenopausal French women found beneficial effects of high phyto-estrogen intake in decreasing risk of ER+ and progesterone receptor positive breast cancer risk. (Touillaud MS et al, J Natl Cancer Inst., 2007)
- In a prospective, blinded, randomized clinical trial with a placebo control in patients with breast cancer, the investigators monitored postmenopausal women who had recently been diagnosed with breast cancer and with a scheduled surgery. These women were divided into 2 groups. One group ate a muffin with 25g of powdered flaxseed while group 2 ate a muffin without flaxseeds. They found that the group that ate the flaxseed muffin had a decrease in tumor cell proliferation and increase in tumor cell death (apoptosis). The researchers concluded that flaxseed had a potential of reducing tumor growth in breast cancer patients. (Thomson LU et al, Clin Cancer Res., 2005)
Besides the listed studies, there have been many other studies in cancer cells, animal models and even other clinical studies that have examined whether flaxseeds, phyto-estrogen and lignan intake are good for reducing the risk of breast cancers. Although there is a potential for flaxseeds to reduce the risk of breast cancer and reduce growth of the tumor, the studies did not consistently show benefits in everyone. The benefits were mainly seen in postmenopausal women. (Calado A et al, Front. Nutr, 2018)
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Flaxseeds and Prostate Cancer Risk
There is limited evidence to support that flaxseed intake is good for reducing the risk of prostate cancer.
In some observational studies, the type of study in which researchers survey what people are eating and then follow them over time to see who develops cancer, have generally found that lignans (phyto-estrogens) in the diet do not protect against prostate cancer. Surprising results from a large study from Europe called the EPIC-Norfolk study initially suggested that dietary lignans may increase prostate cancer risk.(Ward HA et al, Am J Clin Nutr., 2010)
Some studies have suggested that flaxseeds may have a positive effect on prostate health. One study involving men diagnosed with prostate cancer found that those who took flaxseed supplements and were on a low-fat diet saw a reduction in their prostate specific antigen (PSA) levels, a biomarker for prostate cancer. (Azrad M et al, J Med Food, 2013; Heymach JV et al, Cancer Prev. Res (Phila), 2011) Other studies have shown no positive effect of flaxseed and the impact of alpha-linolenic acid on prostate health. (Zhang Q et al, Intl. J of Food Sci & Nutr., 2017)
Therefore, there is inconclusive evidence on the beneficial effects of flaxseed consumption on reducing risk of prostate cancer.
Flaxseeds and Colorectal Cancer Risk
In animal model studies and human clinical studies, flaxseed consumption was shown to have a beneficial effect on colon health associated with reduction in colorectal cancer risk. (DeLuca JAA et al, Curr Oncol Rep., 2018) In a rat study, rats fed with flaxseeds vs a control group showed a significant reduction in precursor lesions in the colon and were found to be chemopreventive. (Williams D et al, Food Chem Toxicol., 2007)
Each of flaxseeds bioactive components including fiber, the omega 3 fatty acid alpha linolenic acid, the phyto-estrogen (lignans) were all found to be good for reducing the risk of colorectal cancers.
Consumption of fiber has been shown to suppress the risk of colorectal cancer via its effect on colonic microbial metabolism. (O’Keefe SJ D, Nat Rev Gastroenterol Hepatol., 2016, Lattimer JM & Haub MD, Nutrients, 2010) The microbiota in our gut can ferment the complex dietary fibers and this provides energy to keep a healthy gut microbiome, maintains the mucus lining of the colon, suppresses inflammation and carcinogenesis.
Alpha-linolenic acid, a component of flaxseeds, the source for omega 3 polyunsaturated fatty acids (PUFA), has been shown to have beneficial anticancer effects. Epidemiological evidence supports the association between dietary intake of omega-3 fatty acids and reduced risk of colorectal cancer. Additionally, PUFA intake also improved the efficacy and tolerability of cancer chemotherapy drugs. The mechanism of action of the anticancer effects associated with PUFA intake has been determined to be due to reduction of inflammatory mediators such as prostaglandin E2. (Cockbain et al, Gut, 2012)
As regards the lignan (phyto-estrogen) constituent of flaxseeds, the observational and interventional studies have produced inconsistent results on whether the phyto-estrogen intake is good for reducing the risk of colorectal cancer. (Viggiani M T et al, Nutrients, 2019)
Side Effects/Negative Effects and Interactions with Flaxseeds
One needs to be cautious while using flaxseeds as these also have certain risks and side effects. One of the major side effects of Flaxseed oil and excessive flaxseed consumption is that it may decrease platelet aggregation and increase bleeding time. Additionally, in combination with herbs such as angelica, clove, garlic, ginger, ginseng, it may further decrease platelet aggregation.
Another side effect of Flaxseed is its ability to lower blood pressure. This side effect may be further enhanced if combined with CoQ10, fish oil and herbs like cat’s claw, lycium. (Naturalmedicines.therapeutic research.com)
Flaxseeds also contain Linoleic acid besides alpha linolenic acid. A study done by the National Institute of Environmental Health Sciences, NIH, showed the inherent dangers/side effects that excessive dietary fatty acids such as Linoleic acid can have on gastric cancer. The study highlighted that Linoleic acid enhanced the sprouting of new blood vessels (angiogenesis) and ‘increased dietary linoleic acid enhanced tumor growth in an animal model.’ (Nishioka N et al, Br. J Cancer, 2011) Excessive dietary Linoleic acid may promote spread and invasion of tumors. (Matsuoka T et al, Br. J Cancer, 2010)
Conclusion
Flaxseed, a popular functional superfood has been shown to have many health benefits. The bioactive constituents of flaxseeds including alpha-linolenic acid, the precursor to omega 3-fatty acids, the phyto-estrogen lignan, the rich fiber content and the other phytochemicals all contribute to the beneficial effects of flaxseeds.
Despite the large number of studies, the evidence on whether flaxseed intake is good for reducing the risk of breast cancer, prostate cancer or colorectal cancer is still inconclusive. There is evidence from preclinical and animal studies on anticancer properties of flaxseeds due to reduction of inflammatory mediators, but we need larger and well designed human interventional studies to confirm the anticancer impact in humans.
Hence, despite all the great properties and benefits of consuming flaxseeds, it has to be taken in moderation and it has to be used in its natural form and not as supplements. Different side effects and negative interactions of Flaxseeds are also reported. For cancer patients undergoing treatment, they should consult with their oncologist and nutritionist regarding consuming a diet rich in flaxseeds due to concerns regarding reduced platelet aggregation and other possible negative effects/side effects and interactions.
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